INSTALLATION INSTRUCTIONS
21/16" AIR / FUEL RATIO MONITOR
®
2650-837L
Installation
1. Disconnect the negative (-) battery cable.
2. Gauge can be mounted in a 21⁄16" dia. hole with brackets supplied.
Gauge can also be mounted in Auto Meter Mounting Cup, or in
Auto Meter Gauges Works Pods.
3. Wire gauge as shown.
Red Wire: Connect to a fused and switched 12V positive source
that is turned on and off with the ignition switch
Black Wire: Connect to good engine ground.
Violet Wire: Connect to oxygen sensor signal wire. Connect to
vehicle wiring harness, not oxygen sensor since some oxygen
sensors use shielded wire.
White Wire: Connect to 12V Dash Lighting. (See Note below)
NOTE: “Models with white wire to be connected to 12V Dash Lighting”
Red
Violet
Powertrain
Control Module
(PCM)
Signal Wire
Note for Lunar Models: Continuous use of lighting, use in excessive heat (over 100 degrees
F.), and use of lighting at full power will reduce the life span of these gauges. It is recommended
that the lighting be wired through the OEM light switch, and that the use of lighting be limited in
extremely hot weather in non-AC cars. It is also recommended that the lighting be dialed down to
less than full power to extend the life of the instruments.
Mounting Sensor
If your vehicle is not originally equipped with an oxygen sensor,
purchase Auto Meter model number 2244. The heated oxygen
sensor comes with a weld in boss, boss plug, and wiring harness
with a weather pack connector. The oxygen sensor should be
installed in a spot where exhaust from all cylinders flows past
it.The oxygen sensor should also be installed as close to the
cylinder head as reasonably possible so that the sensor reaches
operating temperature quickly. If headers are used, the oxygen
sensor should be installed in the collector. If cast iron manifold(s)
are used, install the sensor in the pipe just below the manifold.
Mounting in the left or right side is acceptable. If monitoring of
both sides is desired, a second oxygen sensor can be used and
a switch (purchased locally) can be wired to toggle back and forth
between both sensors.
5 AMP Fuse
Black
Connector
12V Ignition Switch
White
(See Note above)
B
a
t
t
e
r
y
Good Engine
Ground
Oxygen Sensor
The Air / Fuel Ratio Monitor can be used with the following fuels.
Fuels
Unleaded Gasoline
Methanol
Ethanol
Propane
OK for use with Nitrous Oxide.
The Stoichiometric Air / Fuel Ratio is the chemically correct
ratio where theoretically all of the oxygen and all of the fuel are
consumed. The mixture is neither rich or lean.
Stoichiometric Air / Fuel Ratio
12V Dash Lighting
14.7:1
6.5:1
9.0:1
15.7:1
Model 2244
Signal Wire
Heater Ground
Heater +
1
O2 Sensor
Signal
O2 Sensor
Connect
Purple Wire
O2 Sensor Internal
Ground (No Wire)
Powertrain Control
Module (PCM)
O2 Sensor
Signal (High)
O2 Sensor
Ground (Low)
O2 Sensor
Connect Purple Wire
Powertrain Control
Module (PCM)
Oxygen Sensors
O2 Sensor Signal
O2 Sensor
Connect Purple Wire
O2 Sensor Internal
Ground (No Wire)
Heater
Ground
Heater
Power
(+12V)
Powertrain Control
Module (PCM)
O2 Sensor
Signal (High)
O2 Sensor
Ground (Low)
O2 Sensor
Connect Purple
Wire
Heater
Ground
Heater
Power
(+12V)
Powertrain Control
Module (PCM)
All oxygen sensors must be heated to at least 600˚ F before an accurate signal is produced.
WARNING
Do not connect ohm meter to oxygen sensor, or touch wire to ground or
power. Damage to oxygen sensor will result. If a volt meter is to be used, only
use a high impedance (10 mega ohm or higher) digital multimeter.
NOTE: Do not disconnect wire to the computer.
Heated Oxygen Sensors
These sensors have an electrical resistance heater built in to them
and will come to operating temperature usually within 1 minute. These
sensors have 3 or 4 wires, check with vehicle manufacturer, or wiring
diagram for your specific vehicle to learn which wire is the signal.
3 Wire Sensor
Non-Heated Oxygen Sensors
These sensors rely on the hot exhaust gases to bring them to
operating temperature. This may take several minutes and may even
cool off when engine is idling. These sensors have 1 or 2 wires. On
2 wire sensors, one wire is ground and the other is the signal. Check
with vehicle manufacturer or wiring diagram for your specific vehicle
to learn which wire is the signal.
1 Wire Sensor
4 Wire Sensor
2 Wire Sensor
2
Warning
Fouling and/or permanent damage to the oxygen sensor over time will
result if used with any of the following:
• Leaded gasoline and fuel additives containing lead
• 2 cycle gasoline (gas/oil mix)
• Diesel Fuel
• Nitromethane
• Excessively rich mixtures
If the Air/Fuel Ratio Monitor responds sluggish, the oxygen sensor is
probably partially fouled and should be replaced.
When the engine is at heavy load the monitor should indicate rich. At
cruising load the monitor will appear to be bouncing back and forth
between rich and lean. This is normal. The computer is constantly
LED Chart
Lean Range Four red LED’s (.050 to .249V)
Stoichiometric Range Ten yellow LED’s (.250 to .749V)
Rich Range Six green LED’s (.750 to 1.000V)
adjusting the air / fuel ratio for performance and low exhaust
emissions. See back page for more detailed information.
The Air/Fuel Ratio Monitor has 20 LED’s. Four red that indicate lean,
Ten yellow that indicate stoichiometric ratio, and six that indicate
rich. One LED lights up for every 50mV of oxygen sensor output.
3
Air / Fuel Ratio Meter and Oxygen Sensor Operation
1.000
.800
.600
.400
.200
0
10.3 11.8
Rich
A/F Ratio for Gasoline
Lean
13.2
Increasing Oxygen
Sensor Temp.
14.7 16.2 17.6 19.1
Sensor Output Voltage, V
The A/F Ratio Meter is a voltmeter with a range of 0 to 1 Volt. The
meter displays the output voltage of the vehicles oxygen sensor
through 20 LED’s. The first LED will come on at a voltage of .050V,
the second at .100V, the third at .150V, etc (see LED Chart on
previous page).
The stoichiometric (STOICH) air/fuel ratio is the chemically correct
ratio. This means theoretically all of the oxygen and all of the fuel
are consumed. The mixture is neither rich nor lean. However, due to
the fact that combustion is never perfect in the real world, there will
always be a small amount of oxygen left in the exhaust. This small
amount that is left is what the oxygen sensor measures. The smaller
the amount of oxygen that is left in the exhaust, the richer the A/F
ratio is, and the higher the oxygen sensor voltage is. The on-board
computer or Powertrain Control Module (PCM) monitors the voltage
from the oxygen sensor. If the PCM sees an oxygen sensor voltage
greater than .450V, it immediately starts to reduce the amount of fuel
that is metered into the engine by reducing the on time to the fuel
injectors. When this happens, the A/F ratio starts to go in the lean
direction, and the oxygen sensor voltage starts to go down. When the
voltage drops below .450V, the PCM immediately starts to increase
the fuel metered to the engine by increasing the on time to the fuel
injectors to produce a richer A/F ratio. This occurs until the oxygen
sensor voltage goes above .450V. This repeating cycle happens very
fast (many times per second). The PCM is said to be in closed loop. It
is constantly monitoring the oxygen sensor voltage and adjusting the
on time of the fuel injectors to maintain a STOICH A/F ratio. This A/F
ratio produces the lowest harmful exhaust emissions, and allows the
catalytic converter to operate at peak efficiency, therefore reducing
the exhaust emissions further.
due to the fact that the oxygen sensor output changes with the
oxygen sensor temperature and wear. As the sensor temperature
increases, the voltage output will decrease for a given A/F ratio in the
rich area, and increase in the lean area as shown on the graph.
During wide open throttle (throttle opening greater than 80% as
indicated by the throttle position sensor) the A/F ratio will be forced
rich by the PCM for maximum power. During this time the oxygen
sensor will output a rich signal/voltage, but the PCM will ignore
the signal. The signal will be ignored because it is not accurate for
indicating the exact richness. The PCM is now in open loop, and
relies on factory programmed maps to calculate what the on time of
the fuel injectors should be to provide a rich A/F ratio for maximum
power. The A/F ratio meter should indicate rich during this time.
During hard deceleration the PCM will command an extremely lean
mixture for lowest exhaust emissions. This may cause the signal to
go outside the range that the meter will indicate. When this happens,
there will be no LED’s lit on the A/F meter.
Oxygen sensor output voltage vs. A/F ratio for gasoline
Since the oxygen sensor output is very accurate and sensitive at
the STOICH A/F ratio, it will cause the A/F meter LED’s to bounce
back and forth rapidly. A very small change in A/F ratio causes a
large change in oxygen sensor voltage as can be seen on the graph.
This rapid cycling is normal when the PCM is in closed loop and
trying to maintain a STOICH A/F ratio. The oxygen sensor is also
very accurate at indicating an A/F ratio that is richer or leaner than
STOICH. However it can not indicate the exact richness or leanness
For service send your product to Auto Meter in a well packed shipping carton. Please include a note explaining what the problem is along with your phone number. Please specify when you
need the product back. If you need it back immediately mark the outside of the box “RUSH REPAIR,” and Auto Meter will service product within two days after receiving it. ($10.00 charge will be
added to the cost of “RUSH REPAIR.”) If you are sending product back for Warranty adjustment, you must include a copy (or original) of your sales receipt from the place of purchase.
Auto Meter Products, Inc. warrants to the consumer that all Auto Meter High Performance products will be free from defects in material and workmanship for a period of twelve (12) months from date of the
original purchase. Products that fail within this 12 month warranty period will be repaired or replaced at Auto Meter’s option to the consumer, when it is determined by Auto Meter Products, Inc. that the product
failed due to defects in material or workmanship. This warranty is limited to the repair or replacement of parts in the Auto Meter instruments. In no event shall this warranty exceed the original purchase price of
the Auto Meter instruments nor shall Auto Meter Products, Inc. be responsible for special, incidental or consequential damages or costs incurred due to the failure of this product. Warranty claims to Auto Meter
must be transportation prepaid and accompanied with dated proof of purchase. This warranty applies only to the original purchaser of product and is non-transferable. All implied warranties shall be limited in
duration to the said 12 month warranty period. Breaking the instrument seal, improper use or installation, accident, water damage, abuse, unauthorized repairs or alterations voids this warranty. Auto Meter
Products, Inc. disclaims any liability for consequential damages due to breach of any written or implied warranty on all products manufactured by Auto Meter.
12 MONTH LIMITED WARRANTY
SERVICE
FOR SERVICE SEND TO: AUTO METER PRODUCTS, INC. 413 W. Elm St., Sycamore, IL 60178 USA (815) 899-0801
Email us at service@autometer.com
© 2002 Auto Meter Products, Inc 2650-837L 9/23/02
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