Pontiac Fiero 1988 Service Manual page 550

DRIVEABILITY A N D EMISSIONS - F U E L INJECTION (TBI) 6E2-C4-3
An open or ground in the EST circuit will result
in the engine continuing to run, but in a back-up
ignition timing mode (module timing) at a
calculated timing value and the "Service Engine
Soon" light will not be on. If the EST fault is still
present the next time the engine is restarted, a
Code 42 will be set and the engine will operate in
module timing. This may cause poor performance
and reduced fuel economy.
DIAGNOSIS
S Y M P T O M DIAGNOSIS
The ECM uses information from the MAP and
coolant sensors in addition to rpm to calculate spark
advance as follows:
• Low MAP Output Voltage = More spark advance
• Cold engine = More spark advance
• High MAP Output Voltage = Less spark
advance
• Hot engine = Less spark advance
Therefore, detonation could be caused by low MAP
output or high resistance in the coolant sensor circuit.
Poor performance could be caused by high MAP
output or low resistance in the coolant sensor circuit.
If the engine cranks but will not run or
immediately stalls, CHART A-3 must be used to
determine if the failure is in the "DIS" system or the
fuel system.
Code 4 2
If Code 42 is set, that code chart must be used for
diagnosis. If the symptom is "Engine Misses" and the
ignition system is suspected, use CHART C4-D "DIS
Misfire" for diagnosis.
Code 12
Code 12 is used during the Diagnostic Circuit
Check procedure to test the diagnostic and code
display ability of the ECM. This code indicates that
the ECM is not receiving the engine rpm
(REFERENCE) signal. This occurs with the ignition
key "ON" and the engine not running.
SETTING TIMING
Because the reluctor wheel is an integral part of
the crankshaft and the crankshaft sensor is mounted
in a fixed position, timing adjustment is not possible .
ON-CAR SERVICE
M
D I S " A S S E M B L Y (Figure C 4 - 2 )
Remove or Disconnect
1. Negative Battery cable.
2. "DIS" electrical connectors.
3. Spark plug wires. (Note proper relationship of
wires to coils).
4. "DIS" Assembly to block bolts (3).
5. "DIS" Assembly from engine.
|5
Inspect
Crankshaft sensor O-Ring for wear, cracks, or
leakage. Replace if necessary. Lube new O-Ring with
engine oil before installing.
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Install or Connect
1. "DIS" Assembly to engine.
2. "DIS" Assembly to block bolts (3).
Torque to 27 Nm (20 Lbs.Ft.).
3. Spark plug wires to proper coils.
4. "DIS" electrical connectors.
5. Negative battery cable.
CRANKSHAFT SENSOR (Figure C 4 - 3 )
Remove or Disconnect
1. Negative battery cable.
2. "DIS" Assembly (See previous procedure).
3. Sensor screws (2).
4. Sensor from "DIS" Assembly.
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Inspect
Sensor O-Ring for wear, cracks or leakage.
Replace if necessary. Lube new O-Ring with engine
oil before installing.
[HHH| Install or Connect
1. Sensor to "DIS" Assembly.
2. Sensor screws (2)
Torque to 2.3 N-m (20 Lbs.In.)
3. "DIS" Assembly to engine. (See previous
procedure).
4. Negative battery cable.