Actron CP7838 User Manual
CP7838
15825 Industrial Parkway
Cleveland Ohio 44135 USA (EUA)
The Fuel Pressure Tester Kit was designed to help diagnose driveability
problems due to abnormally high or low fuel pressure
Instructions for Professional
Fuel Pressure Tester Kit
English
Safety Precautions
To prevent accidents that could result in
serious injury and/or damage to vehicle or test
equipment, carefully follow safety rules and test
procedures at all times when working on vehicles.
Always wear approved eye protection.
Never use Fuel Pressure Tester Kit on Diesel or
Flex Fuel engines!
Never attach or remove Fuel Pressure Tester Kit
from fuel rail test port with ignition key on.
Always place end of 6 foot bleed-off hose in an
approved container for fuel during testing and
when bleeding off fuel pressure.
Never smoke or have open flames near vehicle.
Vapors from fuel and charging battery are highly
flammable and explosive.
Never permit fuel to spill on hot engine parts. If a
spill or leak occurs, immediately turn ignition
key off, and clean up fuel.
Only use Fuel Pressure Tester Kit for measuring
fuel pressure.
Do not inhale exhaust gases or fuel vapors.
Always keep yourself, tools and test equipment
away from all moving or hot engine parts.
Always make sure vehicle is in PARK
(Automatic transmission) or NEUTRAL (manual
transmission) and parking brake is set. Block
drive wheels.
Never lay tools on vehicle battery. Terminals may
short together causing harm to yourself, tools or
battery.
Never leave vehicle unattended while running
tests.
Always keep a fire extinguisher suitable for fuel/
electrical/chemical fires handy.
Always use extreme caution when working
around ignition coil, distributor cap, ignition
wires, and spark plugs. These components
contain High Voltage when engine is running.
Complete all Pre-Testing Checks before
beginning fuel pressure testing.
Always follow vehicle manufacturers warnings,
cautions and service procedures.
Always operate vehicle in a well ventilated area.
Fuel Pressure Tester Description
10
1
2
Voltage: 16V
Tension de 16V
Tensión: 16V
50
40
1 Rubber Boot: Boot is used to protect gauge and maintain
appearance.
2 Dial Face: Contains measurement scales that show amount
of fuel pressure present in fuel system.
3 Pressure Relief Button: Used to relieve fuel pressure in
20
10
3
60
30
psi
70
300
400
200
500
100
80
600
700
90
kPa
100
gauge hose before disconnecting gauge hose from fuel rail.
4 Bleed-Off Hose: A 6 foot hose that bleeds off fuel pressure
when pressure relief button is pressed. Never use a bleed-off
hose shorter than 6 foot.
Important: Always make sure end of bleed-off hose is in an
4
9
approved container for fuel at all times during testing and when
bleeding off fuel pressure!!
5 Gauge Hose: Hose that carries fuel to the gauge, so that
pressure can be measured.
5
8
7
6 GM/Chrysler Test Port Adapter: Adapter is used to connect
gauge hose to GM, Chrysler, and other vehicles equipped with a
schrader valve test port on fuel rail.
7 Ford Test Port Adapter: Adapter is used to connect gauge
hose to Ford vehicles equipped with a schrader valve test port on fuel rail.
6
8 GM TBI Test Adapter: Adapter is used to connect gauge hose to GM TBI vehicles NOT equipped
with a schrader valve test port.
9 M12 X 1.25 Banjo Bolt Adapter: Adapter is used to connect gauge hose to Asian, European and
select domestic vehicles equipped with fuel Banjo Bolt Connections.
10 Dual Manifold Test Adapter: Adapter is used to connect gauge hose to vehicles with rubber hose
connections on the fuel rail, fuel line, or fuel filter.
Instructions in English French and Spanish
Instructions en Anglais, Français et Espagnol
Instrucciones en Inglés, Francés y Español
Fuel Injection System Theory
English
There are two basic types of fuel injection systems currently being used. The first type is called
port or multi-port fuel injection. In this system, fuel injectors spray fuel directly into intake manifold
behind intake valve. These systems typically have one fuel injector per cylinder. The second type is
commonly called Throttle Body Injection (TBI) for GM and Chrysler vehicles or Central Fuel Injection
(CFI) for Ford vehicles. These systems use one or two fuel injectors mounted on top of intake manifold.
They spray fuel into throttle body similarly to a conventional carburetor.
Fuel Injectors
Fuel Pressure Regulator
Pressure Line
Fuel Injectors
Fuel Rail
Test Port
Fuel Pressure
Regulator
Pressure
Line
Return Line
Ford CFI Throttle Body GM Multi-Port Fuel Injection
Return
Line
Fuel Injectors
Fuel System Components
Before doing any fuel pressure testing, it is a good idea to understand how fuel system
components work and how they relate to one another. The fuel pump pumps fuel from the fuel tank to
the fuel pressure regulator and fuel injectors. Fuel pressure regulator divides fuel between the pressure
line and return line. The fuel in the pressure line goes to fuel injectors, while fuel is returned to fuel tank
through the return line.
Fuel Injectors
ort
Test P
ail
Fuel R
Vacuum Port
Fuel Pressure Regulator
Fuel Rail
Return Line
Fuel Injectors
Fuel Filter
Fuel Tank
Fuel Tank: A large container that holds vehicles
supply of fuel.
Fuel Pump Filter: A filter that is usually located
in fuel tank. Its function is to prevent foreign
particles from reaching the fuel pump. A clogged or
restricted fuel pump filter can cause low fuel
pressure readings. When replacing a fuel pump it
Pressure Line
Fuel Pump
is a good idea to replace the fuel pump filter.
Fuel Pump: An electric motor that pumps fuel
into the fuel system at a constant pressure. It is
mounted in the fuel tank or on the frame. Some
vehicles have more than one fuel pump.
Return Line: Path way for excess fuel to return
to the fuel tank.
Fuel Pump Filter
Pressure Line: A pressurized fuel line that
carries fuel from the fuel tank to the fuel injectors.
Fuel Filter: A filter that is located in-line with the
pressure line. Its function is to prevent foreign
particles from reaching the fuel injectors. A
clogged or restricted fuel filter can also cause low
fuel pressure readings. This is the only fuel
system component that requires periodic
replacement. Refer to vehicle owners manual for
replacement interval.
Fuel Rail Test Port: A schrader valve located on
the fuel rail that allows easy connection of a fuel
pressure gauge to measure fuel pressure. Do not
confuse this valve with the schrader valves that are
used for recharging air conditioning systems.
Fuel Pressure Regulator: The fuel pressure
regulator is connected across the pressure line
and return line. It contains a spring loaded valve
assembly that opens to allow fuel to move into the
return line, when the pressure line fuel pressure is
exceeded. It is used to keep a constant fuel
pressure drop across the fuel injectors. Some fuel
pressure regulators have a vacuum port so fuel
pressure can be adjusted based on engine load.
These are commonly called vacuum actuated
(compensated) fuel pressure regulators. A leaking
fuel pressure regulator can cause low fuel
pressure readings and hard starting problems.
Fuel Rail: The fuel rail assembly is bolted to the
intake manifold. Its purpose is to hold the fuel
injectors in place and to deliver pressurized fuel to
the fuel injectors.
Fuel Injectors: A precision valve that is controlled
by a solenoid. Fuel injection is controlled by the
amount of fuel pressure, and the size and duration
of the valve opening. Fuel injectors contain a filter
used to prevent very small particles from clogging
the valve. Leaking fuel injectors will cause fuel
pressure to slowly decrease when the ignition key
is on and engine is off.
English
Pre-Testing Checks
1. Read Safety Precautions.
2. Do a thorough visual and hands-on inspection
of the engine and fuel system. Look for loose or
cracked electrical wiring, battery cables,
ignition wires, and fuel or vacuum lines.
3. Verify that the battery is fully charged and fuel
tank has an adequate supply of fuel.
4. Verify that the inertia switch on certain Ford/
Lincoln/Mercury vehicles has not been tripped.
(The inertia switch is usually located in the
trunk.)
5. Verify that all fuel system fuses are good.
Fuel Pressure Testing Procedures
This test procedure explains how to make
fuel pressure measurements on vehicles while
ignition key is on and while engine is at idle. The
procedure also explains the safest way to connect
and disconnect fuel pressure tester kit from
vehicles. If fuel pressure readings measured in this
test procedure are not within vehicles
manufacturers specification, then use vehicle
service manual along with fuel pressure tester kit
to service problem. This test procedure does not
contain any vehicle specific diagnostics.
1. Read all SAFETY PRECAUTIONS and PRE-
TESTING CHECKS.
2. Apply a lightweight household oil to rubber O
rings on test adapters.
3. Turn Ignition Key OFF.
4. Install Gauge.
END OF BLEED OFF HOSE
MUST BE PLACED IN AN
APPROVED FUEL CONTAINER
6. Verify fuel vapor recovery system and gas cap
are in good condition.
7. Verify that manifold vacuum is within
manufacturers specification which is typically 1820 inches at idle.
8. Look for fuel leaks and wipe up any spilled fuel
immediately.
9. If engine will not start, check ignition system for
spark. If no ignition spark is present, refer to
vehicle service manual for No Start Diagnostics.
10. Inspect wire harnesses and electrical
connectors for damaged or corroded parts.
11. Check other electrical systems including
ignition and car computer system.
For GM/Chrysler vehicles with test port...
Note: A right-angle large schrader adapter, part
number 0180-1299 is available for closeclearance connections.
Remove Test Cap.
Screw GM/Chrysler test port adapter to fuel
rail test port until finger tight.
Note: Always wrap a shop rag around fuel rail
test port when attaching test port adapters.
This is a precaution in case a small amount of
fuel leaks out while attaching adapters.
50
40
60
30
70
300
400
200
500
80
20
100
600
700
10
90
kPa
100
psi
Test Port
Adapter
Shop Rag
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