Auto Meter 4375 - Manual (Page 4)

12 mONTH LImITeD WARRANTY
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.
SeRVICe
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.
FOR SERVICE SEND TO: AUTO meTeR PRODUCTS, INC. 413 W. Elm St., Sycamore, IL 60178 USA (815) 899-0801
Email us at [email protected]
© 2002 Auto Meter Products, Inc 2650-837L 9/23/02
Air / fuel Ratio meter and Oxygen Sensor Operation
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.
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
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.
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
Vo
lta
ge
, V
Oxygen sensor output voltage vs. A/f ratio for gasoline