Table of Contents
Advertisement
Calibration
Calibration of the F/A Monitor and the UEGO sensor can be easily performed using air.
To bring the system into calibration, put the sensor in air and adjust the calibration
potentiometer (CAL POT) on the control module using the calibration screwdriver provided.
First turn the potentiometer counter-clockwise until the CAL LED (yellow) is off, then turn
the potentiometer slowly clockwise until the CAL LED just lights. If the CAL POT cannot
be turned to where the CAL LED is off then the sensor is bad.
For best accuracy, the F/A Monitor and UEGO sensor should be on for at least 20 minutes
prior to calibration. However, calibrating at approximately three minutes after powering up a
cold (i.e. room-temperature) UEGO sensor is equivalent.
For best accuracy, the UEGO sensor should be held with its tip pointing down in still air
during calibration. Calibrating with the sensor in an "off " engine is not recommended due to
the possibility of residual exhaust gases remaining in the exhaust system.
Fuel Type Compensation
The standard F/A Monitor output is for gasoline (measurement range of 0.055 to 0.125 F/A)
with a fuel H:C ratio of 1.85 and an O:C ratio of zero. If a fuel of a different composition is
used, Equation 2 can be used to compensate (i.e. correct) the F/A Monitor's output.
F/Acorr = [(m + 16p + 12)/(2.368 x (m - 2p + 4))] x F/Ameas
where: F/Acorr is the F/A for the fuel of H:C=m and O:C=p composition.
F/Ameas is the F/A output by the F/A Monitor.
m > (2p - 4).
Pressure Compensation
All wide-range exhaust sensors have a pressure sensitivity. Errors occur when the sensor is
operated at pressures different from the pressure at which it was calibrated.
pressure come about from changes in weather, altitude changes, and engine backpressure.
There is no sensitivity to pressure at stoichiometric (Lambda = 1) conditions. The sensitivity
gets greater the further from stoichiometric the engine is operated. Increases in pressure
make the sensor read further from stoichiometric (i.e. if lean, reads leaner, if rich, reads
richer). For example, an increase in exhaust pressure of 127 mmHg above the calibration
pressure (which would result from calibrating at 1 mile above sea level and then driving
down to sea level) would make a 0.079 F/A engine read 0.080 or a 0.052 F/A engine read
0.050. To compensate for pressure use Equation 3.
If Equation 2 (fuel type compensation) and Equation 3 (pressure compensation) are to both to
be used, apply Equation 3 first, then Equation 2.
8
[Equation 2]
Changes in
Advertisement
Table of Contents
