Pontiac Fiero 1988 Service Manual page 435

6 E - S DRIVEABILITY AND EMISSIONS - FUEL INJECTION
Throttle Position Sensor (TPS)
Values read will be the voltage as seen by the
ECM. The voltage should be the TPS specification
with the throttle closed and go up to about 5 volts
with throttle wide open (WOT).
Throttle Angle
Displayed, in percent, is the amount the throttle is
open. 0% is closed throttle, 100% is wide open throttle.
Oxygen (O2)
Sensor
The reading will be read out in millivolts (mv)
with a range from 1 to 999 mv. If the reading is
consistently below 350 (350 mv), the fuel system is
running lean as seen by the ECM; and if the reading is
consistently above 550 (550 mv), the system is
running rich.
PROM ID
In this position, information is used for assembly
verification only. PROM ID is useful only when the
vehicle is equipped with the original ECM and PROM
or Mem-Cal.
RPM
Reading displays engine rpm. It is often useful if
extra reference pulses are suspected. A sudden high
rpm indication while at a steady throttle would
indicate electrical interference (EMI) in the reference
circuit. This interference is usually caused by ECM
wires too close to ignition secondary wires or an open
distributor ground circuit.
MPH
Displayed is vehicle speed, useful in checking TCC
application speed or speedometer accuracy.
MAF
This displays the amount of air passing the Mass
Air Flow (MAF) sensor, in grams per second. It is
useful when comparing the airflow between a problem
vehicle and a known good one. Normal readings at
idle are about 4 to 8 grams. If a MAF code is set, this
reading will display the ECM default value.
Airflow
This display should be the same as MAF when
there are no failures in the MAF sensor circuit. When
an MAF code is set, however, this value will not
change, and will indicate the gm/sec that the failure
has detected.
Coolant Temperature
Engine temperature is displayed in Celsius
degrees. After the engine is started, temperature
should rise steadily to about 85-95° C, then stabilize
when the thermostat opens.
Manifold Air Temperature (MAT) Sensor
This displays temperature of the intake manifold
air. It should read close to ambient air temperature
when the engine is cold, and rise as underhood and
engine temperatures increase.
Manifold Absolute Pressure (MAP)
The MAP sensor produces a low signal voltage
when manifold pressure is low (high vacuum) and a
high voltage when the pressure is high (low vacuum).
With the ignition "ON" and the engine stopped,
the manifold pressure is equal to atmospheric
pressure, and the signal voltage will be high. This
information is used by the ECM as an indication of
vehicle altitude and is referred to as BARO.
Comparison of this BARO reading with a known good
vehicle with the same sensor is a good way to check
accuracy of a "suspect" sensor *. Readings should be
the same ± .4 volt.
* A MAP sensor has a colored plastic insert visible
in the connector cavity. Sensors with the same insert
color are identical in calibration. The harness
electrical connector color also should be the same as
the sensor insert color.
Vacuum (Differential Pressure) Sensor
The vacuum sensor produces a low signal voltage
when manifold vacuum is low, and a high voltage
when the vacuum is high .
With the ignition "ON" and the engine stopped,
there is no vacuum, so the voltage is low (under 1
volt). With the engine idling the vacuum is high so the
voltage is high (over 3 volts).
A vacuum sensor has a colored plastic insert
visible in the connector cavity. Sensors with the same
insert color are identical in calibration. The harness
electrical connector color also should be the same as
the sensor insert color.
Baro
This displays barometric pressure. The ECM uses
this information to adjust for altitude and pressure.
This value will vary depending on barometric
pressure and altitude. Some vehicles use a dedicated
baro sensor, while others take a MAP reading before
the engine is started, and at various times during
engine operation.