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06820

Mityvac 06820 User Manual [en, de, es, fr]

Users Manual
www.mityvac.com
Users Manual
English / Spanish / French / German
©
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ENGLISH
CONTENTS
The Pump..................................................4
The Automotive Vacuum System...............6
Diagnosing Mechanical Engine
Conditions........................................8
Positive Crankcase Ventilation
System...........................................10
Exhaust Gas Recirculation (EGR)...........10
Spark Delay Valves (SDV)......................15
Electrical/Vacuum Solenoid ....................16
Thermal-Controlled Vacuum
Switching Valves............................16
Brake .....................................................17
Frnech Section .......................................48
German Section .....................................48
Spanish Section......................................70
These pumps are not approved for use with combustable materials such as gasoline, kerosene, or diesel fuel. Serious injury or damage may occur if pump is used with these fluids.
TO AVOID PERSONAL INJUR Y AND/OR VEHICLE DAMAGE: While some precautions are specified in this manual, and should be noted to avoid personal injury or vehicle damage, it is not possible for these cautions to cover all conceivable ways in which service or testing might be done, or all possible hazardous consequences of each way, nor could Lincoln possibly know or investigate all such ways. It is therefore the responsibility of anyone using this manual or any other Mityvac® product, to satisfy him or herself completely that neither personal safety nor vehicle safety will be jeopardized by the service methods selected. Any such injury or damage is entirely the user’s responsbility. This device is not to be used in any manner on the human body.
© Copyright 2003 by Lincoln Industrial, Inc All rights reserved. This volume may not be reproduced in whole or part in any form without written permission from the publisher. TRADEMARK NOTIFICATION Mityvac® SilverlineYM and Dual ConverterTM are all trademarks of Lincoln Industrial Printed in Taiwan
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THE PUMP
The vacuum pump is an extremely versatile service tool that can be used to test a variety of automotive systems and perform a number of useful tasks. Though the pump has obvious uses for testing various vacuum motors, control valves and vacuum sources, its applica­tions don’t end there. Almost any part or system that requires proper sealing, pressure or vacuum to operate can be tested with the vacuum pump. The pump and its accessories also transfer fluids, help to bleed brakes and aid in other tasks. The pump also meets diagnostic tool requirements when such tools are specified for some state vehicle inspec­tion programs. This section will describe the pump, give specifications, tell how to use the pump and provide some service tips to help you keep your pump in tip-top shape.
DESCRIPTION
The hand held vacuum pump is simple, accurate, easy to use and has many applications. Although the pump comes in several different versions, the basic unit consists of a pump body, moveable handle, vacuum gauge, vacuum fitting and a safety capped pressure fitting. The pump is easily held in your hand, and when the handle is squeezed, a vacuum is drawn at the vacuum fitting. If the vacuum of the pump is connected to a closed container or system, the gauge will show the vacuum level. If the pressure fitting is attached to the container or system, a pressure will be generated but will not show on the gauge. If it is desired to read the amount of pressure, a separate pressure gauge is available.
V ACUUM RELEASE
There are two basic methods of releas­ing vacuum at the pump. The first method is the Trigger Vacuum Release. It is a straight lever, which must be pulled straight back to release the vacuum. This action allows air to enter the system, thus relieving the vacuum.
The second method is a spring action rotary release. By slowly turning the vacuum release tee, the vacuum can be gradually released. By turning the tee quickly, the vacuum will be released quickly.
SAFETY CAP
The small cap on the pressure fitting is pressed on with a friction fit. It can be removed with a twisting pull. The cap is used to prevent any fluids (brake fluid, etc.), which may have accidentally been pulled into the pump, from squirting into the user’s eyes. For this reason, the cap should always be in place when using the pump, except when using the pressure fitting. The pump will last for many years when cared for properly. See PROPER CARE in this section.
SPECIFICATIONS
Application Measurement
Maximum Vacuum
At Sea Level Approx. 23-25” Hg.
Stroke V olume
Standard 1 cu. in. Repairable 1 cu. in. Superpump 2 cu. in.
Silverline 1 cu. in. Maximum Pressure Unassisted
Standard 7 psi.
Repairable 12 psi.
Superpump 7 psi.
Silverline 15 psi. Assisted
Standard 16 psi.
Repairable 95 psi.
Superpump 12 psi.
Silverline 30+ psi. Gauge accuracy
15-20 in. HG. 3%-2%-
3% of full range.
MAINTENANCE KITS are available only for repairable pumps, which have been assembled with visible screws. Non­repairable pumps have been chemically sealed and cannot be opened without damaging the pump. Except for lubrica­tion, no repairs should be attempted on these units. See LUBRICATION in this section.
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USING THE PUMP
The vacuum pump is simple to use. In most cases, the pump is either attached directly to a component, used in place of a vacuum line or connected into a vacuum circuit with a tee connector. The pump can be operated as a test instru­ment in three ways:
1) When vacuum is desired for a test, the movable handle of the pump is simply squeezed with your hand, as in clenching your fist. Continue strokes until desired vacuum is indicated on the gauge.
2) The pump can be connected into a vacuum circuit and used to measure existing amounts of vacuum, just as any vacuum gauge would be used. When used this way, do not pump the handle, or incorrect readings may result.
3) The pump can also be used as a pressure pump by removing the safety cap and connecting to the pressure fitting. When the pump handle is released from the closed position, pressure is created. Additional pressure can be applied manually pushing in the piston pump rod.
CAUTION: Always be sure the safety
cap is in place unless the pressure fitting is being used. Other sections of this manual outline specific uses for the pump.
test instrument. Do handle it carefully! Don’t drop or handle roughly as the gauge accuracy may be affected. Don’t lay on hot manifold or expose to direct flame. Don’t leave plastic pump in a hot car as it may warp. Care for your pump and it will give you years of trouble free service.
LUBRICATION
The factory installed lubricant is silicone oil and should provide very long service. If you find it necessary to lubricate your pump, use silicone oil. If unavailable, you may use DOT 5 (not DOT 3) silicone­based brake fluid or a salad vegetable oil. Do not use petroleum based fluids or spray lubricants (WD-40, motor oil, etc.), as these will damage the pump.
PROPER CARE
Your pump is a sturdily built, precision
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THE AUTOMOTIVE
VACUUM SYSTEM
This manual deals with vacuum, how it is used in various automotive systems and how the vacuum pump can be used to test and diagnose these systems. This section discusses what vacuum is, how it is measured, where it comes from on an automobile, the system for distributing and using vacuum, and some trouble­shooting basics.
WHA T IS VACUUM?
Put simply, vacuum is empty space, and may exist as either a total or partial vacuum. Vacuum does not, of itself, create power. Rather, power for vacuum devices depends on the presence of atmospheric pressure. The atmosphere exerts a pressure of 14.7 pounds per square inch (psi) on everything at sea level. If a portion of the air is removed from one side of a diaphragm (partial vacuum), the atmospheric pressure will exert a force on the diaphragm. The force is equal to the pressure difference times the diaphragm area (FIGURE 1). Generally, the less air (greater vacuum) in a given space, the more the atmo­sphere tries to get in and the more force is created.
HOW IS VACUUM MEASURED?
In the United States, vacuum is commonly measured in inches of Mercury (“Hg). It may also be measured in centimeters of Mercury (cm Hg) and kiloPascals (kPa). Atmospheric pressure will support a column of Mercury in a manometer gauge about 30 inches high or about 76cm high. This is the barometric pressure in “ Hg which varies as the weather changes. Vacuum readings in “ Hg are really negative pressure readings. For exam­ple, 30” Hg vacuum would be a complete vacuum. Half of a complete vacuum would be 15” Hg. A gasoline engine at idle usually pulls about 16-22” Hg vacuum. On deceleration, because the throttle is closed, the vacuum will increase. The pump will pull about 25” Hg as indicated on its vacuum gauge which is calibrated in both “ Hg and kPa.
WHY ENGINES CREATE VACUUM
Vacuum is created when air is with­drawn from a given volume, or a sealed volume is increased. That is why vacuum is available in an engine. On the intake stroke, the piston moves down, this creates a partial vacuum because the volume of the cylinder is increased. Air cannot rush through intake system fast enough to totally fill the space created when the piston moves down (FIGURE
2). This is the most common automotive vacuum supply source.
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GASOLINE VS. DIESEL VACUUM
Because a diesel engine does not produce as much vacuum as a gasoline engine, a mechanical vacuum pump must be employed to operate vacuum devices. The pump is useful in testing devices on both types of engines.
VACUUM DISTRIBUTION
All modern automobiles have a vacuum distribution system (FIGURE 3), consisting of lines, hoses, fittings and vacuum devices. This system must be leakproof. If it is not, the engine air/fuel
mixture will be leaned out by the extra air entering the system through the leaks, thus causing problems such as burned exhaust valves, uneven idle, stalling, pre­ignition, burned spark plugs, etc. Additionally, any vacuum operated device affected by the vacuum leak will not function properly. A normal gasoline engine should develop 16-22” Hg of intake manifold vacuum at idle. This is an indication that the engine is breathing properly. If the vacuum is lower, the engine is running less efficiently. The lower the manifold vacuum, the less efficiently the engine is running and the lower the gas mileage will be. The vacuum distribution system supplies vacuum to vacuum motors (servos) in the air conditioning, power brake booster, speed control servo, emission controls, manifold absolute pressure (MAP) sensor, and automatic transmission control systems. In older vehicles,
vacuum is also supplied to the distributor vacuum advance or retard mechanism. These devices can be connected directly to manifold vacuum, or can be controlled through electric solenoids, thermostatic switches, or other vacuum controls.
TROUBLESHOOTING THE VACUUM SYSTEM
Most vacuum problems can be traced to leaks, which occur in hoses, connectors, motor diaphragms or valves. Pinched lines or clogged valves will also not allow vacuum flow. Problems can also be traced to improper mechanical operation of devices driven by vacuum motors. The vacuum pump can be used to measure the amount of vacuum in a hose. The vacuum gauge feature is very useful for detecting a fluctuating vacuum supply or a leaky enables you to check all types of vacuum operated devices. On a vacuum motor, for example, the pump is used to evacuate the diaphragm chamber, which allows you to check the mechanical operation of the device as well as the amount of vacuum, required to actuate it. Test for leaking diaphragm by applying 10” Hg vacuum to the device (FIGURE 4). Observe the gauge to see if the needle drops after the actuator stops moving. If the needle continues to drop, a leaking diaphragm is indicated. If the diaphragm is okay, the vacuum should hold for one minute with the needle steady.
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DIAGNOSING
MECHANICAL ENGINE CONDITIONS
VACUUM GAUGE CHECKS & DIAGNOSIS
The pump’s vacuum gauge readings give indications of possible mechanical problems, but they are not foolproof. Observe the gauge carefully and follow the vacuum readings with further tests, where possible, to confirm your diagno­sis. Do not look for the engine to produce specific (numerical) amounts of vacuum. Much more important than specific numbers is the range of the vacuum readings and the movement of the needle (FIGURE 5). Important things to notice about the needle movement are HOW the needle moves (in a smooth or jerky manner, erratic, etc.), what direction it moves, whether movement is regular or varying, and how far the needle moves.
The following gives some examples of what to look for and the meanings of a variety of vacuum gauge reading should be 16-22” Hg and steady.
Normal Engine
Run engine at idle and connect the pump to an intake manifold vacuum port. Watch the needle’s movement on the gauge. At idle, the vacuum gauge reading should be 16-22” HG and steady.
BURNED OR LEAKING V AL VE SPRING
At idle, burned or leaking valves will cause the pointer on the gauge to drop to a low reading and return to normal at a regular interval. The needle will drop from 1” Hg at regular intervals whenever the defective valve attempts to close.
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STICKING VALVE
A sticking valve will exhibit a rapid, intermittent drop from the normal pointer indication. This is unklike the regular drop that characterizes a burned or leaking valve.
A sticking valve condition may be pin­pointed by directly applying a lightweight oil to each valve guide. When the sticking valve is reached, the situation will be temporarily remedied.
WEAK OR BROKEN V ALVE SPRING
Weak valve springs are indicated when the pointer of the vacuum pump gauge fluctuates rapidly between 10” and 21”Hg at idle. The fluctuations will increase with engine speed. A broken valve spring will cause the needle to fluctuate rapidly at a regular interval. Again this will occur every time the valve attempts to close.
WORN V A LVE GUIDES
Worn valve guides admit air which upsets the air/fuel mixture. The vacuum gauge reading will be lower than normal and will fluctuate rapidly in a range of about 3” Hg. As the speed of the engine is increased, the needle will steady.
LEAKING PISTON RING
Vacuum at idle will be low but steady at about 12” to 16” Hg. Open the throttle and allow the engine to pick up speed to about 2000 RPM. Then, close the throttle quickly. The pointer should jump 2” to 5” Hg above its low steady reading. A lesser gain may indicate faulty rings, and a complete cylinder leakage or compression test should be done.
BLOWN CYLINDER HEAD GASKET
At idle, the vacuum pump gauge pointer will fluctuate between normal and a low reading. The needle will drop sharply about 10” Hg from a normal reading and return each time the defective cylinder or cylinders research firing position.
EXHAUST RESTRICTION TEST
An exhaust restriction will cause normal or near normal performance at engine idle but cause very poor engine performance under load, or at higher speeds.
1) Connect the pump hose to an intake manifold vacuum fitting. Operate the engine at idle and note the vacuum reading and needle movement. Compare readings and movements against descriptions listed for burned valves and late ignition or valve timing.
2) Watch the vacuum gauge as engine speed is increased to approximately 2500 RPM.
3) An increase in vacuum over that obtained at idle indicates an exhaust system that is free of restrictions.
4) If the needle drops toward zero as engine RPM is increased, either an exhaust restriction or an over-active Exhaust Gas Recirculation (EGR) valve is causing the problem.
5) Test the EGR valve separately. If it is found to be in good condition, the problem is a restricted exhaust. Check and replace if necessary.
INCORRECT IDLE AIR/FUEL MIXTURE
When the needle on the gauge drifts slowly back and forth at idle, over a range of 4” to 5” Hg, the fuel mixture is too rich. A lean mixture will cause an irregular drop of the needle over about the same range.
INTAKE MANIFOLD OR AIR INDUCTION LEAKS
If there are any air leaks in the air induction system, the pump’s gauge needle will be about 3” to 9” below normal but will remain steady.
LATE IGNITION OR VALVE TIMING
An extremely low but steady reading at idle indicates late ignition or valve timing, or a uniformly close setting of the valve lash. Perform separate tests to determine which of these problems, if any, have affected the engine.
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POSITIVE CRANKCASE VENTILA TION SYSTEM
SYSTEM OPERATION
The Positive Crankcase Ventilation (PCV) system is used on all modern engines to reduce air pollution by providing a more complete scavenging of crankcase vapors. Air is drawn through a filter located in the air cleaner, through a hose in the valve cover, into the crankcase, across and up into the rear of the intake manifold or opposite valve cover, through the PCV valve, through a hose, into the intake manifold. Intake manifold vacuum draws in all vapors from the crankcase to be burned in the engine.
When air flow through the carburetor or throttle body is high, added air from the PCV system has no effect on engine operation.
However, at idle, air flow through the carburetor or throttle body is so low that any large amount added by the ventilation system would upset the air/fuel mixture, causing a rough idle. For this reason, the PCV valve restricts the ventilation system flow when intake manifold vacuum is high.
SERVICE PROCEDURES
After a period of operation, the PCV valve may become clogged and reduce the amount of crankcase ventilation. The PCV valve should be replaced periodically to prevent the formation of acids in the crankcase and the build up of excessive crankcase pressure, which could force engine oil out past the seals. Use the
following procedure to check the PCV system using your pump:
1) Inspect the system for kinked, plugged or deteriorated hoses. Check to be sure all hoses are connected properly. Repair as necessary.
2) Connect your pump to an intake manifold port and check the vacuum reading of the warmed and idling engine.
3) Clamp off the vacuum hose to the PCV valve. The engine speed should decrease 100 RPM to indicate the loss of the calibrated air leak into the intake manifold. The vacuum gauge reading should increase slightly indicating that the vacuum leak has been plugged. If this does not happen, replace the OCV valve and/or replace any damaged, plugged or loose hoses.
4) If the engine is idling too slow or is rough, this may be caused by a clogged PCV valve or hose. Do not adjust the idle speed without first checking the PCV system.
5) After installing a new PCV valve, always adjust the idle speed, and if possible, the idle air mixture. The installation of the wrong valve may cause too much vapor to flow through the system if the calibrated bleed is too large. This will lean out the air/fuel mixture excessively. If the opening is too small, the plugging effect will be nullified, emissions will increase, crankcase acids will form and oil leaks may develop. Be sure you get the correct PCV valve for your car.
EXHAUST GAS RECIRCULA TION (EGR)
An Exhaust Gas Recirculation (EGR) sys­tem is used on most modern engines to reduce Oxides of Nitrogen (NOx) emis­sions. During the combustion process, nitrogen, which makes up 80 percent of the air, will mix with oxygen at tempera­tures above 2,500° F. During the combus­tion process, temperatures in the cylinders go well above 3,500° F providing for the formation ideal condi­tions for the formation of Nox.
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SYSTEM OPERATION
To reduce the formation of NOx, it is necessary to lower the combustion temperature. This is most often done by introducing exhaust gases back into the combustion chamber through the use of an EGR valve. The EGR valve (FIGURE 6) may be operated by ported vacuum from above the throttle plates or by a sophisti­cated control system that modulates the amount of EGR depending on the temper­ature of the coolant, ambient air tempera­ture, engine speed or load.
An EGR valve that does not have a sophisticated control system must be fully closed with a vacuum of less than 2” Hg and begin to open with 2-8.5” Hg of vacuum. At idle and wide-open throttle, the ported vacuum supply is low and the valve should be closed.
Some cars have a Back-Pressure Transducer Valve (BPV) to modulate the operation of the EGR system. Some cars have a Venturi Vacuum Amplifier (VVA) to do the same job. The effect is to modulate the amount of EGR according to the load on the engine. To improve cold driveabili­ty, most cars are equipped with some type of vacuum control device to shut off EGR while the engine is cold.
there is at least 4” to 5” Hg vacuum available. Remember also that clogged exhaust passages that lead to or from the valve can restrict the flow even if the valve is opening.
An EGR valve that remains open will cause the engine to idle roughly, die at idle, and lose power and full-throttle smoothness. The valve usually fails to close due to dirt or damage in the valve seat area. An EGR valve can operate nor­mally with the engine warm but remain open when the engine is cold. That condition could be caused by a faulty thermal switching device that does not cut off the vacuum supply when the engine is cold.
EGR systems fail in two ways. Either the valve may fail due to a fault of its own, such as a ruptured diaphragm, or due to a loss of control vacuum. Always check to be sure that there is vacuum at the hose connected to the EGR valve, before replacing the valve. Connect the pump to the vacuum supply hose at the EGR valve and check to be sure that at 2000 RPM
SERVICE PROCEDURES ­GENERAL TEST EXCEPT GM OR BACK-PRESSURE CONTROLLED TYPE)
If the symptoms of an engine lead you to believe that an EGR valve is staying open, follow this procedure:
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1) Connect a tachometer to the engine and run the engine at idle speed until it reaches normal operating tempera­ture. Use the pump to check for at least 10” Hg vacuum at the valve. Replace the hose and note the engine RPM.
2) Remove the vacuum hose from the valve and notice whether engine RPM increases.
3) If engine speed does increase, there may be some type of problem in the vacuum control circuit. Check the routing of all vacuum hoses.
4) If engine speed or the quality of idle changes, remove the valve and check the pintle and valve seat to make sure both are clean. If they are not, replace the valve, gasket and adapter if it is burned, warped or damaged. If the engine symptoms lead you to believe that the EGR valve is staying closed, follow the procedure below:
1) Operate the engine at idle until it reaches full operating temperature. Use the pump to check for the presence of 10” Hg vacuum at the valve. Set the engine speed at approximately 2000 RPM. Plug the vacuum supply hose. Connect the vacuum pump to the EGR valve and apply 10” to 15” Hg vacuum. 2) The diaphragm should move to the open position and a decrease in engine RPM should be noted. If not, the valve is defective or the manifold passages are plugged. Release the vacuum on the EGR valve.
3) The diaphragm should move to the closed position and an increase in engine RPM should be noted. Return the engine to idle and turn it off.
4) Connect the pump to the EGR valve and test by applying at least 9, Hg of vacuum to the diaphragm and watch the gauge carefully for any vacuum loss.
5) If the valve diaphragm does not move, or cannot hold vacuum, replace the EGR valve.
SERVICE PROCEDURES GM EGR V AL VES
General Motors produces three types of EGR valves. Each valve can be identified by the design of its diaphragm plate (FIGURE 7). The first valve is a ported vacuum EGR that has only a circular rib on the back of its diaphragm plate. The second is a positive back-pressure valve with X-shaped ribs that are raised only slightly above the plate. Finally, there is a negative back-pressure valve with X­shaped ribs raised well above the diaphragm plate. Both the ported vacuum and negative back-pressure valves are tested the same way. A separate test is listed to check the positive back-pressure valve.
GM PORTED VACUUM AND NEGATIVE BACK-PRES­SURE EGR TEST
1) Make sure all vacuum hoses are routed according to the emission control label.
2) Check the vacuum connection to the EGR valve for obstructions.
3) Connect the pump between the EGR valve and the carburetor or vacuum source. Start engine and run at the idle until it reaches operating
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temperature (195° F approx). Check for vacuum at 3000 RPM; it should be 5 Hg minimum.
4) If no vacuum is available in step 3, check for it between the EGR thermal vacuum switch (TVS) and the carburetor. If the vacuum is available there, replace the TVS.
5) If the vacuum supply between the EGR and the carburetor is adequate, connect the pump to the EGR valve inlet. Depress the valve diaphragm and apply approximately 10” Hg of vacuum to the EGR. Release the diaphragm and record the time it takes for the diaphragm to return to its seated position.
6) If it takes less than 20 seconds for the valve to seat, replace the valve.
GM POSITIVE BACK­PRESSURE EGR TEST
1) Follow steps 1 through 4 of the ported vacuum and negative back­pressure EGR test.
2) Remove the EGR valve from the engine. Connect the pump to the EGR vacuum inlet and apply 10” Hg of vacuum. The valve should not open. If it does, replace the valve.
3) Continue the test by keeping the vacuum applied and shooting a low­pressure stream of air into the valve’s exhaust inlet. The valve should now open. If it does not, replace the valve.
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EGR VENTURI VACUUM AMPLIFIER
Some engines utilize a Venturi Vacuum Amplifier that uses the weak vacuum sig­nal from the throat of the carburetor to allow the passage of the stronger intake manifold vacuum to operate the EGR valve. On most applications the amplifier provides a 2” Hg boost to the Venturi sig­nal (FIGURE 8).
SERVICE PROCEDURES
1) Start engine, run at idle until it reaches normal operating tempera­ture.
2) Make sure the intake manifold hose to the amplifier is properly connected. On those systems with a reservoir, remove the hose from the reservoir and use a tee connector to join the hose to the intake manifold vacuum hose.
3) With separate lengths of hose and different connectors, bypass any and all vacuum valves or coolant con­trolled valves between the amplifier and the EGR valve.
4) Use a tee connector to attach the pump into the vacuum line between the amplifier and EGR valve.
5) Increase engine speed to 1500/2000 RPM and release the throttle. Let the engine return to idle speed and remove the vacuum hose at the carburetor Venturi. The vacuum reading should be within ± .3” Hg of
the specified boost for that amplifier if other than zero boost is specified. Zero boost may read from 0 to .5” Hg. Replace amplifier if out of specifica­tion.
6) Increase engine speed. Watch vacuum gauge and release accelera­tor after speed of 1500/2000 RPM is reached. If the vacuum gauge reading shows an increase greater than 1” Hg during acceleration period, the amplifier should be replaced.
7) Remove the pump from the output vacuum line and reconnect hoses, but still bypass other valves. Connect the pump and apply 2” to 4” Hg of vacuum to port on the amplifier which is normally connected to intake manifold vacuum. The EGR valve should operate and engine idle should drop or become erratic. If the EGR valve fails to move, replace the amplifier.
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BACK-PRESSURE TRANS­DUCER V ALVE (BPV) OPERATION
The Back-pressure Transducer Valve (BPV) controls the amount of EGR according to the load on the engine. An exhaust pressure probe extends into the exhaust crossover passageway to sample the exhaust gas pressure. During light engine loads, the pressure in the exhaust passageway is relatively low while during wide-open throttle operation (WOT), the pressure is highest. This pressure signal is transmitted to a diaphragm in the BPV and is used to control the amount of vacuum applied to the EGR valve (FIGURE 9).
SERVICE PROCEDURES
1) Remove the air cleaner and plug the intake manifold fitting. Start the engine
SP ARK DELA Y V ALVE (SDV)
OPERATION
Spark Delay Valves (SDV) are used to delay vacuum to the distributor vacuum advance actuator during hard accelera­tion, to delay the action of the Thermactor Air Induction Reaction (AIR) system during prolonged engine idling, and to delay the application of vacuum to the automatic choke pulldown diaphragm during cold engine operation. A sintered metal valve is installed in the vacuum advance (outer) diaphragm of the distributor control unit on some engines. The purpose of the valve is to delay the spark advance during rapid acceleration to minimize the formation of NOx. The sintered metal is porous and allows vacuum to bleed through the valve acting like an orifice of about 0.002” in diameter. Control is obtained by varying the number of discs in each valve assembly so that the time delay features can be tailored to the engine (FIGURE 11).
and bring it to normal operating temperature. Position the fast-idle cam follower on the second step of the fast-idle cam (to obtain about 1500 RPM), and then note engine speed on a tachometer, and use the pump to check the source vacuum at an intake manifold port (FIGURE 10). Note this reading.
2) Tee your pump into the vacuum pas­sageway to the BPV and the reading should be 1-2” Hg of vacuum. Replace the BPV if it is not within specifica­tions.
3) Leave the vacuum gauge at this location, remove the hose to the EGR valve, and plug the hose opening. Read the vacuum pump gauge, which should be the same as the intake manifold vacuum reading. If it is not within 2” Hg of the source vacuum, replace the BPV valve.
repaired and must be replaced every 12,000 miles because the pores of the sintered metal fill with dust, which can slow the performance of the valve. NOTE: The spark delay valve is a one­way unit that must be installed with the Black side facing the carburetor vacuum port. To determine if a spark delay valve is operating correctly, the following service procedure should be used:
1) With the transmission in neutral, set the carburetor to the fast-idle position, remove the spark-delay valve and tee your vacuum pump into the hose leading to the carburetor spark port.
SERVICE PROCEDURES
The time delay of the valve varies with engine application. The different valves may be identified by color and part number. Spark delay valves cannot be
Page Number - 15
2) Record the vacuum reading, which should be between 10-16” Hg.
3) Pinch off the vacuum hose and observe if the gauge maintains the vacuum level. If the gauge shows that the vacuum drops with the hose pinched off, the gauge or vacuum hose has an external leak, which must be corrected.
4) Now, connect the Black side of the spark-delay valve to the vacuum hose leading to the carburetor spark port. Connect a section of vacuum
ELECTRICAL/V ACUUM SOLENOID
SERVICE PROCEDURES
1) Disconnect vacuum and electrical connectors from the solenoid. Connect the pump to port “B” and attempt to apply vacuum with pump. Vacuum should be released through port “A” (FIGURE 12).
2) Using jumper wires, connect negative solenoid terminal to ground and apply 12 volts to the positive terminal. Apply vacuum to port “B”. Vacuum should hold and not bleed off. If the solenoid does not hold vacuum, replace solenoid.
3) With solenoid still energized, move vacuum pump to port “A”. Attempt to apply vacuum. Vacuum should be released through the air filter and no vacuum should be present at port “B”.
hose to your vacuum pump and attach the other end to the distributor end of the spark delay valve. Observe the time in seconds for the gauge to reach 6” Hg, with a 10-16” Hg vacuum source. If the vacuum reaches the 6” Hg level in less than two seconds, regardless of type, the SDV should be replaced. When checking the valve, care must be taken to prevent oil or dirt from getting into the valve as this will impair its function.
THERMAL-CONTROLLED V ACUUM-SWITCHING V ALVES
SERVICE PROCEDURES
These control valves are called Ported Vacuum Switches (PVS) when used on Ford engines. Thermal Ignition Control (TIC) valves when used on Chrysler products, and Distributor Thermal Vacuum-Switches (DTVS) when used on General Motors engines. The two-port valve is used to stop EGR while the engine is cold. This type of thermal switch is needed to provide good driveability by limiting the entrance of EGR until the engine is warmed up. The three-port valve is commonly called a cooling system PVS because it switches the vacuum source to the distributor from ported to full intake vacuum.
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The four-port valve has been used in some Ford engines to bypass the spark delay valve and cut out the EGR system when the engine is cold.
SERVICE PROCEDURES
Follow this procedure to test the two-port vacuum-switching valve:
1) Apply 10” Hg of vacuum to the bottom port of the valve with your vacuum pump and measure the results with a second vacuum gauge as shown in the accompanying illustration (FIGURE 13).
2) The valves are color coded and the Green valve should open and pass vacuum at 68° F, the Black valve at 100° F.
3) If full vacuum flows through the valve when heated, it is okay. If there is no vacuum flow or there is vacuum flow when the coolant is cold, replace the valve.
Follow this procedure to test the three­port vacuum-switching valve:
1) Apply 10” Hg of vacuum with your vacuum pump to the middle port of the valve with a vacuum gauge at each of the other two ports.
2) Refer to the same color-coded valves and same temperature specifications as for the two-port valve above. If the vacuum switches at the specified temperature, the valve is okay. If there is no vacuum to the lower port above the specified temperature, replace the valve.
The four-port valve must be tested two times, once at the top two ports and once at the bottom two ports as shown in the accompanying illustration (FIGURE 14).
1) Apply 10” Hg of vacuum with your vacuum pump to one of the top two ports. The valve should hold vacuum when above the specified operating temperature.
2) If flow occurs when the valve is warm, replace it.
3) For the lower two ports, vacuum must pass through the valve only when the engine is warm; otherwise, replace the valve.
BRAKE BLEEDING
Many brake systems today feature Anti­Lock functions and electronic controls. Many of these systems use a high pres­sure electric pump to keep the system pressurized. When bleeding or servicing, these systems require special proce­dures and cautions. Always observe the following precau­tions when servicing Anti-Lock brake system:
• ALWAYS wear safety goggles when servicing high pressure brake systems.
• ALWAYS depressurize the ABS system prior to adding fluid or attempting service or repair.
• Unless instructed to by the manufac­turer’s procedure, NEVER open a bleeder valve or loosen a hydraulic line while the ABS system is pressur­ized.
• ONLY use recommended brake fluids. DO NOT use silicone brake fluid in ABS equipped vehicles.
• Always refer to an appropriate repair manual for additional information an Anti-Lock brake systems.
DEPRESSURIZING ANTI­LOCK BRAKE SYSTEMS
Always refer to the vehicle owner’s manual or appropriate service manual for additional information on depressurizing procedure. The procedure will work on most Anti-Lock brake systems. Ensure ignition switch is in the OFF position or disconnect the negative battery cable.
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Pump the brake pedal 25-40 times. A noticeable change is felt, continue to pump the pedal a few additional times. This should eliminate most system pressure. Open fluid reservoir or brake lines carefully. Top off reservoir fluid and reconnect battery cable when finished.
BLEEDING ANTI-LOCK BRAKE SYSTEMS
Always refer to the vehicle owner’s manual or appropriate service manual for
manufacturer’s brake bleeding procedure. The front brakes on most Anti-Lpck brake systems may be bled in the conventional manner. Most hydraulic pump/pressure accumulator units are fitted with a bleeder valve which must be bled when the system has lost fluid or is being replaced. Some vehicles require that the system be pressurized when the rear brakes are bled. Various Asian, European, and domestic manufacturers use bleeding procedures which require specialized equipment.
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BRAKE LINE BLEEDING
Most low and soft pedal problems are caused by air in the hydraulic lines, which requires bleeding of the hydraulic system. By using the pump with brake bleeding accessories, the system can be bled easily. Follow a wheel-to-wheel sequence beginning with the wheel closest to the master cylinder. The Kit provides a simple, clean, and quick method for bleeding the fluid lines in the automotive brake system. The creation of a vacuum in the reservoir jar causes fluid to be drawn into the reservoir jar. It should be noted that a tiny stream of bubbles may be noticed in the hose after all of the air is bled from the lines. This is caused by air seeping around the threads of the loosened bleeder fitting and being drawn back through the fitting by the suction of the pump. Once the air is removed from within the system, these tiny bubbles will in no way jeopardize the bleeding operation, since they are present only at the fitting and do not enter the system. If you wish, you can put grease or Teflon tape around the threads of the fitting to eliminate most of the bubbles. The correct bleeding procedure follows:
1) Always make certain that the master cylinder reservoir is filled and that a supply of new, clean brake fluid of the proper type is on hand to top off the reservoir as the fluid level drops during bleeding. Make sure that all the bleeding fittings are clean prior to beginning of the bleeding procedure.
2) Bleed the hydraulic system in the following order: a) Master cylinder bleeder fittings, if
equipped. (If installing a new or rebuilt master cylinder, follow the bench bleeding procedure which follows.)
b) Bleeder fittings on the combination
valve, if equipped.
c ) Wheel cylinders and calipers in
succession beginning with the wheel closest to the master cylinder, and working to the farthest one.
NOTE: Wheel balancing sequence varies
among manufacturers. Follow manufacturer’s recommended sequence (if known). Procedure
given in this article specifies to begin bleeding wheel closet to master cylinder. Regardless of sequence used, always ensure all air is purged from system.
3) Slip 1-1/2” of tubing between the pump and the lid of reservoir jar at port marked “TO PUMP” (FIGURE 15).
4) Attach 3-1/2” plastic hose to the bottom of the cap (if not already attached).
5) Affix at least a 12” piece of tubing to the other reservoir jar port. Be certain that the cover of the reservoir jar is secure, but don’t overtighten.
6) Select the appropriate adapters. The snap-over adapters (L-shaped) are different sizes (small, medium, large). They should fit snugly over the brake bleeding fitting in order to seal properly. The tapered adapters fit inside the thru-hole of fitting and will generally seal well when inserted tightly with a pressing and twisting motion. Attach adapter to reservoir hose.
7) Place wrench on brake bleeding fitting; attach adapter and pump assembly and pump 10-15 times. NOTE: If bubbles coming out of the fitting are very small and even in size, the air is probably coming from within the system. It is not necessary to eliminate these bubbles as they do not affect brake operation. If desired, these bubbles can generally be eliminated by placing grease or Teflon tape around the threads, to act as a seal.
8) Open fitting slightly, only enough to cause the fluid to enter jar (usually 1/4 to 1/2 turn).
9) After evacuating about 2” of fluid into jar, tighten fitting. Keep master cylinder full. Repeat all previous steps on all remaining wheels. If fluid is not drawn into the jar after opening the fitting, make certain the lid of the jar is tight. You will not be able to produce the necessary vacuum in the jar if the lid does not fit securely. Occasionally some dirt will get into the brake line, in which case the pump may not be totally effective. If this happens, have someone touch the brake pedal once
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lightly, with the bleeding valve open, then proceed to use the pump.
MOTORCYCLE BLEEDING
PROCEDURE
Before bleeding the system, ensure that
1) the brake caliper pistons are free to move within the calipers.
2) the master cylinder piston is free to return to the end of its stroke, and
3) inspect the line to ensure that all fittings are tight.
FRONT BRAKE
1) Pump brake lever to seat caliper pads against rotor.
2) Cover gas tank with plastic protective sheet if using DOT 3 fluid (not necessary if using DOT 5 fluid).
3) Remove master cylinder reservoir cap and fill reservoir.
4) Attach a 5/32” ID connection hose to brake bleeding fitting.
5) Pump several times to create vacuum. Crack bleeder valve with box wrench, extracting fluid into reservoir. (Stop and add fluid when master cylinder begins to get low. Do not allow air to enter line.) At this point, all air should be out of system and line full of fluid. (Note: if air is entering the pump hose from around bleeder
fitting, remove bleeder fitting and apply Teflon tape to threaded portion of bleeder screw only. This will prevent air seepage around threads of bleeder screw.)
6) While maintaining vacuum on the pump line, tighten bleeder fitting.
7) Top off reservoir and reinstall cover. Check brake by pumping lever several times. Pedal should have a positive, solid feel. If not, repeat bleeding process as more air may have entered the system. Inspect line to ensure all fittings are tight. If brake still feels slack, consult a service technician. For dual disc front brakes, repeat bleeding process as though there are two separate systems.
REAR BRAKE
Removing all air from the rear brake line is the same as for the front. The rear brake reservoir is usually located beneath one of the side covers.
1) Remove the master cylinder cap and fill to near full.
2) Attach the pump hose to the bleeder fitting and pump the handle several times to create a vacuum.
3) Crack the bleeder with a box wrench. Because of the short line, most of the air should be evacuated the first time.
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4) By closing the valve and repeating the process, all of the air should be eliminated from the system. Stop and add more fluid when master cylinder gets low.
5) Top off and recap the reservoir.
TROUBLESHOOTING
1) If, after bleeding procedure, the brake continues to be unresponsive, you may have water in the system, in which case it will need to be disas­sembled and cleaned by a qualified service technician.
2) If the brake squeaks slightly after bleeding, the disc and pads must be cleaned.
3) Although DOT 3 fluid is recommended by most manufacturers, it has a tendency to collect moisture - which causes the common discoloration you see - and that means decreased efficiency. DOT 5 is silicone based and does not have the same tenden­cy to collect moisture. It also has a higher tolerance. DOT 5, however, is not always easy to find and the two types of fluid must not be mixed.
4) Rubber hoses are supplied stock on most motorcycles, but they have a tendency to expand, which may result in a spongy brake feel after a lot of riding. Braided steel line will not expand like this. There is also a hose adapter and 5/32” ID hose in the kit for bleeding hydraulic motorcycle brakes. Be sure the caliper and master cylinder pistons are free and all fittings are tight. Cover the gas tank with rubber or plastic protective sheet. Connect the adapter and 5/32” ID hose to the end of the long tube and connect to caliper bleeder fitting. Bleed as with an automobile.
greatly decreases the chance that any air will be caught in the cylinder upon reinstallation. This bleeding technique utilizes this Kit. Follow this procedure:
1) Plug outlet holes of the master cylinder and gently clamp it in a vise with the push rod end slightly elevated. NOTE: Damage may result if master cylinder is clamped by the bore or if reservoirs are clamped too tightly.
2) Fill the master cylinder with an approved type brake fluid and keep it filled at all times during the procedures.
3) Remove a plug from the master cylinder and attach the proper adapter to this master cylinder outlet port. Connect the pump tube to the reservoir jar and the jar tube to the adapter (FIGURE 16).
4) Pump the pump and observe air and fluid flowing into the reservoir until clear, bubble-free fluid appears.
5) Plug the outlet tightly and repeat step 4 on the other outlet ports.
6) Clamp master cylinder in a vise with the push rod end down slightly. Slowly slide the master cylinder push rod back and forth about 1/8”, until no air bubbles can be seen in the reservoirs.
7) Remount the master cylinder with the push rod end up and follow steps 3 & 4 on all outlet ports. Plug ports tightly. The master cylinder is now free of air and ready to install.
BENCH BLEEDNG THE MASTER CYLINDER
Whenever a master cylinder has been removed from a vehicle or a new one is being installed, the master cylinder must be bench bled. Failure to bench bleed is the main reason for unsuccessful master cylinder replacement. Bench bleeding
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DOMESTIC CAR & LIGHT TRUCK WHEEL LUG NUT SPECIFICATIONS
Application Ft. Lbs. (N.m)
Domestic Cars
Chrysler Motors & Ford Motor Co. FWD Models 90-100 (122-136) RWD Models 85-95 (115-129) General Motors Corp. Aluminum Wheels 90-100 (122-136) Steel Wheels 80-90 (109-122)
Domestic Trucks
Jeep 75-85 (1 02-115) All Others 1/2” Stud 85-95 (115-129) 9/16” Stud 130-145 (177-197) 5/8” Stud 190-200 (258-272)
IMPORT CAR & LIGHT TRUCK WHEEL LUG NUT SPECIFICATIONS
Application Ft. Lbs. (N.m)
Acura & Honda 80 (109) Audi & BMW 80 (109) Infiniti & Nissan 72-87 (98-118) Lexus & Toyota 76 (103) Mercedes-Benz
190, 300D, 300E, 400E, 500E, C220, C280, E320, E420 & E500 80 (109) 300SD, 300SE, 400SEL, 500SEL S320, S350, S420 & S500 111 (150)
Peugeot
Aluminum Wheels 55 (75)
Steel Wheels 45 (61) Porsche 94 (128) Volkswagen
Vanagon 123 (167)
All Others 72-95 (98-129) Volvo
700/900 Series 63 (85)
All Others 80 (109) All Others
Aluminum Wheels 70-90
Steel Wheels 55-65 (75-88)
LAWN MOWER APPLICATIONS
1. Priming circuit of the Lawn Boy and similar engines.
a. Connect pump to the hose
and bulb assembly as shown in Fig. 17.
b. Seal off vent hole in primer
bulb (if present) with finger as shown in Fig. 17. Draw a vacuum on the primer and hose. The bulb should collapse and hold a vacuum until finger is released.
Figure 17
2. Carburator Float Needle and Seat Assembly. a. Use dual converter pump and put
selector on pressure. b. Connect the pump to the fuel inlet. c. Pressurize to 7 psi minimum. d. Must hold 7 psi with carburator
inverted as shown on Fig. 18.
Figure 18
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3. Fuel Tank and Fuel Valve Assembly. a. Use dual converter pump and put
selector on vacuum.
b. Connect pump to the tank outlet.
(See Fig. 19.) Make sure the fuel valve is closed.
c. Pull a vacuum on the fuel valve.
A good valve will hold a vacuum without leaking.
d. Put selector on pressure, open
fuel valve (if equiped). Install fuel cap on tank filler opening.
e. Seal off vent hole in fuel cap and
pump air into fuel tank. Not more than 2 or 3 psi. A good fuel tank will hold the air pressure without leaking. (See Fig. 20.)
Figure 19
Figure 20
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FRANÇAIS
T ABLE DES MA TIÈRES
La pompe ...................................................26
Le système automobile à dépression...........27
Diagnostic des conditions mécaniques
du moteur............................................30
Système de recyclage des gaz du carter....32
Recyclage des gaz d’échappement.............33
Soupapes de délai d’allumage......................38
Électrovalve de dépression de commande
de ralenti.............................................39
thermo-régulées.................................40
Freins...................................................................41
Section Anglaise...........................................2
Section Allemande.......................................48
Section Espagnloe......................................70
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LA POMPE
La pompe à vide est un outil très polyva­lent qui peut être utilisé pour une variété de tests de systèmes automobiles et une multitude de tâches utiles. Bien que la pompe soit évidement utile pour tester des moteurs d’aspiration, robinets de réglages et sources d’aspiration, son usage ne se limite pas à cela. Presque tous les systèmes qui ont besoin pour fonctionner de pression, de dépression ou d’étanchéité appropriées peuvent être soumis à des essais avec la pompe à vide. La pompe et ses accessoires permettent également de transférer des liquides, de purger les freins et d’exécuter plusieurs autres tâches. La pompe est aussi conforme aux spécifications d’outils de diagnostics, lorsque ces outils sont spécifiés pour des programmes d’inspection automobile d’état. Cette section du manuel décrit la pompe, ses spécifications, fournit des instructions sur son mode d’emploi et des conseils pour garder votre pompe en bon état de marche.
de vide. C’est un simple levier qui doit être tiré en arrière pour casser le vide. Cette action laisse entrer l’air dans le système, cassant ainsi le vide.
La deuxième méthode utilise un bouton rotatif à ressort. En tournant lentement le té de suppression de vide, le vide est cassé lentement. En tournant le té rapidement, le vide est cassé rapidement.
BOUCHON DE SÉCURITÉ
Le petit bouchon sur le raccord de pression est emmanché en force avec un ajustement serré. Pour l’enlever, il faut tirer en tournant. Le bouchon empêche les liquides qui sont entrés accidentellement dans la pompe, comme le liquide de frein, d’éclabousser les yeux de l’utilisateur. Pour cette raison, le bouchon doit être toujours en place lors de l’utilisation de la pompe, sauf quand vous utilisez le raccord de pression. La pompe vous donnera plusieurs années de service si elle est bien entretenue. Consultez ENTRETIEN dans cette section.
DESCRIPTION
La pompe à vide manuelle est simple, précise et facile d’emploi pour de nom­breuses applications. Bien que la pompe soit offerte dans plusieurs versions différentes, le modèle de base est composé d’un corps de pompe, d’une poignée mobile, d’un manomètre d’aspiration, d’un raccord d’aspiration et d’un raccord de pression à bouchon de sécurité. La pompe tient facilement dans la main, et lorsque vous serrez la poignée, une dépression est crée au niveau du raccord d’aspiration. Si l’aspiration de la pompe est branchée à un système ou à un récipient fermé, le manomètre indique le niveau d’aspiration. Si le raccord de pression est branché au système ou au récipient, une pression est générée, mais le manomètre ne la montre pas. Un manomètre distinct est offert pour indiquer le niveau de pression.
CASSER LE VIDE
Il existe deux méthodes élémentaires pour casser le vide à la pompe. La première méthode utilise la manette de suppression
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SPÉCIFICA TIONS
Application Mesure
Aspiration maximum
Au niveau de la mer Environ 23 à
25 po Hg (585 à 635 mm Hg)
Volume par course
Modèle standard 16,4 cc. Modèle réparable 16,4 cc. Modèle Superpump 32,8 cc.
Modèle Silverline 16,4 cc. Pression maximum (Sans assistance)
Modèle standard 48 kPa.
Modèle réparable 83 kPa.
Modèle Superpump 48 kPa.
Modèle Silverline 103 kPa. Avec assistance
Modèle standard 110 kPa.
Modèle réparable 650 kPa.
Modèle Superpump 83 kPa.
Modèle Silverline> 206 kPa. Précision du manomètre
15 à 20 po Hg 3%-2%-3%
(381 à 508 mm Hg). de la gamme
complète.
DES NÉCESSAIRES D’ENTRETIEN
sont disponibles uniquement pour les pompes réparables qui sont assemblées avec des vis visibles. Les pompes non réparables sont scellées avec des produits chimiques et ne peuvent pas être ouvertes sans endommager la pompe. Aucune réparation ne doit être entreprise sur ces modèles, à l’exception du grais­sage. Consultez GRAISSAGE dans cette section.
UTILISA TION DE LA POMPE
La pompe à vide est facile d’emploi. Dans la plupart des cas, la pompe est con­nectée directement à un composant, utilisée à la place d’une conduite d’aspiration ou branchée dans un circuit de mise en dépression avec un raccord en T. La pompe peut fonctionner comme instrument d’essai des trois manières suivantes :
1) Quand la dépression est désirée pour un essai, serrez simplement la poignée mobile, comme si vous serriez le poing. Continuez de pomper jusqu’a ce que le niveau de dépression désiré soit indiqué sur le manomètre.
2) La pompe peut être connectée à un circuit de mise en dépression et être utilisée pour mesurer le niveau de dépression actuel, comme le ferait tout autre manomètre à dépression. N’appuyez pas plusieurs fois de suite sur la poignée lorsque la pompe est utilisée de cette manière car de mauvaises mesures pourraient en résulter.
3) En enlevant le bouchon de sécurité et en connectant le raccord de pression, la pompe peut aussi fonctionner comme pompe de pression. La pression est créée quand la poigné de la pompe est relâchée de la position fermée. Pour une pression supplémen­taire, appuyez manuellement sur la tige de la pompe à piston.
ATTENTION : Assurez-vous toujours que le bouchon de sécurité est en place sauf si vous utilisez le raccord de pression. Dans d’autres sections de ce manuel, vous pouvez trouver des utilisations spécifiques de la pompe.
ENTRETIEN
Votre pompe est un instrument de mesure précis, construit solidement. Manipulez- la avec soin ! Ne faites pas tomber la pompe et ne la manipulez pas brutale­ment, car la précision du manomètre peut en être affectée. Ne posez pas la pompe sur un moteur chaud et ne l’exposez pas à une flamme ouverte. Ne laissez pas la pompe en plastique à l’intérieur d’une automobile chaude. La pompe pourrait se déformer. La pompe vous donnera plusieurs années de service si elle est bien entretenue.
GRAISSAGE
Le lubrifiant appliqué en usine est une huile de silicone et doit rester effectif pendant une longue durée. Si vous avez besoin de lubrifier votre pompe, utilisez de l’huile de silicone ou bien, si vous n’en trouvez pas, un liquide pour les freins à base silicone DOT 5 (pas DOT 3) ou même de l’huile végétale alimentaire. N’utilisez pas de liquide à base de pétrole ni de lubrifiant aérosol (par exemple WD­40, huile de moteur, etc.) car ils peuvent endommager la pompe.
LE SYSTÈME À
DÉPRESSION AUTOMOBILE
Page Number - 27
Ce manuel traite de la dépression, de son utilisation dans divers systèmes automo­biles et de l’emploi de la pompe à vide pour contrôler et diagnostiquer ces systèmes. Cette section explique le concept de dépression, sa mesure, sa provenance sur les automobiles, le système de distribution et d’utilisation de dépression, et des principes de base de dépannage.
QU’EST-CE QU’UNE DÉPRESSION ?
Une dépression est tout simplement de l’espace vide, et elle peut exister comme vide partiel ou total. La dépression ne crée pas de puissance par elle-même. La puissance pour les accessoires à vide dépend de la présence de pression atmosphérique. L’atmosphère exerce une pression de 101,3 kPa sur tout objet au niveau de la mer. Si une partie de l’air est enlevée d’un côté d’un diaphragme (vide partiel), la pression atmosphérique exerce une force sur le diaphragme. La force est égale à la différence de pression multipliée par l’aire du dia­phragme (FIGURE 1). Généralement, moins il y a d’air dans un espace (vide plus élevé), plus l’atmosphère cherche à pénétrer et plus la force créée est élevée.
MESURE DE LA DÉPRESSION
Aux États-Unis, la dépression est généralement mesurée en pouces de mercure (po Hg). Elle peut aussi être mesurée en millimètres de mercure (mm Hg) et en kiloPascals (kPa). La pression atmosphérique supporte une colonne de mercure dans un manomètre d’environ 765 mm (30 pouces) de haut. Ceci est la pression barométrique en mm Hg qui varie selon les variations de la météo. Les mesures de dépression en mm Hg sont en réalité des indications de pression négatives. Par exemple, une dépression de 765 mm Hg serait un vide complet. La moitié d’un vide complet serait 382 mm (15 po) Hg. Un moteur à essence tournant au ralenti génère normalement une dépression de 16 à 22 po Hg (400 à 560 mm Hg). Lors des décélérations, parce que le papillon des gaz est fermé, la dépression augmente. La pompe
génère environ 25 po Hg (635 mm Hg) comme indiqué sur le manomètre gradué en po Hg et kPa.
CRÉA TION DE DÉPRESSION PAR LES MOTEURS
Une dépression est créée quand de l’air est retiré d’un certain volume ou bien lorsqu’un espace scellé est agrandi. C’est pourquoi une dépression est présente dans un moteur. Pendant la course d’admission, le piston descend en créant un vide partiel car le volume du cylindre est augmenté. L’air ne peut pas passer suffisamment vite dans le système d’admission pour remplir complètement l’espace créé par le déplacement du piston (FIGURE 2). C’est la source de dépression automobile la plus fréquente.
LA DÉPRESSION DU MOTEUR À ESSENCE ET CELLE DU MOTEUR DIESEL
Étant donné qu’un moteur diesel ne produit pas autant de dépression qu’un moteur à essence, une pompe mécanique est nécessaire pour opérer les accessoi­res à dépression. La pompe est aussi utile pour vérifier les équipements sur les deux types de moteur.
SYSTÈME DE DISTRIBUTION DE DÉPRESSION
Toutes les automobiles modernes présentent un système de distribution de dépression (FIGURE 3) composé de conduites, flexibles, raccords et acces­soires à dépression. Ce système doit être étanche. Sinon, le mélange de carburant et d’air sera appauvri par l’air rentrant par
Page Number - 28
les fuites, causant des soupapes d’échappement et des bougies brûlées, un ralenti irrégulier, le calage du moteur, un allumage prématuré, etc. De plus, tous les instruments commandés par dépres­sion affectés par la fuite ne fonctionner­ont pas correctement. Normalement, un moteur à essence génère une dépression de 16 à 22 po Hg (400 à 560 mm Hg) dans le collecteur d’admission au ralenti. Ceci indique que la dépression du moteur s’effectue correct­ement. Si elle est moins forte, le moteur tourne moins efficacement. Plus la dépression est faible, moins le moteur tourne efficacement, et plus la consom­mation kilométrique est élevée. Le système de distribution de dépression fournit la dépression aux servomoteurs à vide dans les systèmes de climatisation, le servofrein, le servo de régulateur automatique de vitesse, les contrôles d’émission, le capteur de pression absolue du collecteur d’admission, et les systèmes de commande de la boîte de vitesses automatique. Dans les véhicules plus anciens, la dépression est également fournie au mécanisme à dépression d’avance ou de retard d’allumage. Ces instruments peuvent être branchés directement à l’aspiration du collecteur d’admission ou commandés par des solénoïdes, des interrupteurs thermosta­tiques ou autres commandes à dépres­sion.
DÉPANNAGE DU SYSTÈME À DÉPRESSION
La plupart des problèmes de dépression peuvent être attribués à des fuites dans les flexibles, connecteurs, diaphragmes ou soupapes. Des conduites pincées ou des soupapes bouchées ne permettent pas non plus la circulation de la dépres­sion. Des problèmes peuvent aussi être causés par le fonctionnement mécanique incorrect d’un dispositif entraîné par un moteur à vide. La pompe à vide permet également de mesurer le niveau d’aspiration dans un flexible. Le manomètre est utile pour détecter une fluctuation de dépression ou une fuite, et permet de vérifier tous les types d’accessoires à vide. Sur un moteur à vide, par exemple, la pompe est utilisée pour évacuer la chambre du diaphragme, vous permettant de vérifier le fonctionnement mécanique du dispositif ainsi que le niveau de dépres­sion requis pour l’activer. Vérifiez que le diaphragme n’a pas de fuite en appli­quant une dépression de 10 po Hg (254 mm Hg) sur l’équipement. Observez le manomètre. Si l’aiguille chute lorsque l’actionneur a fini de bouger, le dia­phragme présente une fuite. Si le diaphragme ne présente pas de fuite, la dépression doit rester stable pendant une minute, l’aiguille du manomètre restant immobile.
Page Number - 29
DIAGNOSTIC DES CONDITIONS MÉCANIQUES DU
MOTEUR
VÉRIFICA TIONS ET DIAGNOSTICS DU MANOMÈTRE À VIDE
Les mesures du manomètre à vide de la pompe indiquent les possibilités de problème mécanique, mais ces diagnos­tics ne sont pas parfaits. Observez soigneusement le manomètre et vérifiez les mesures avec des tests supplémen­taires, lorsque c’est possible, pour vérifier vos diagnostics. Ne vous attendez pas à ce que le moteur produise une dépression spécifique. La plage des mesures du manomètre et le mouvement de l’aiguille (FIGURE 5) sont plus importants que ces chiffres spécifiques. Ce qui est important, c’est d’observer la MANIÈRE dont l’aiguille bouge (brusque, progressive, erratique, etc.), le sens dans lequel elle bouge, si le mouvement est régulier ou variable, et l’amplitude de déplacement de l’aiguille.
La figure suivante montre des exemples de ce qu’il faut rechercher et la significa­tion des mesures de manomètre à vide qui doivent rester stables, entre 16 et 22
po Hg (400 et 560 mm Hg).
MOTUER NORMAL
Faites tourner le moteur au ralenti et connectez la pompe à un port d’aspiration du collecteur d’admission. Regardez le déplacement de l’aiguille sur le manomètre. Au ralenti, le manomètre doit afficher une valeur stable de 16 à 22 po Hg (400 à 560 mm Hg).
RESSORT DE SOUP APE BRÛLÉE OU QUI FUIT.
Au ralenti, des soupapes brûlées ou qui fuient peuvent causer une chute de l’aiguille du manomètre à une valeur plus basse avec retour à une valeur normale à intervalles réguliers. L’aiguille chute de 1 po Hg (25 mm Hg) à intervalles réguliers quand la soupape défectueuse essaie de
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