Pontiac Fiero 1988 Service Manual page 641

6E3-B-2 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (PORT)
INTERMITTENTS
Problem may or may not turn "ON" the "Service Engine Soon" light, or store a code.
DO NOT use the Trouble Code Charts in
Section "A" for intermittent problems. The fault
must be present to locate the problem. If a fault is
intermittent, use of Trouble Code Charts may result
in replacement of good parts.
• Most intermittent problems are caused by
faulty electrical connections or wiring. Perform
careful check as described at start of Section
"B" Check for:
Poor mating of the connector halves, or
terminals not fully seated in the connector
body (backed out).
Improperly formed or damaged terminals.
All connector terminals in problem circuit
should be carefully reformed to increase
contact tension.
Poor terminal to wire connection. This
requires removing the terminal from the
connector body to check. See Introduction to
Section "6E"
• If a visual check does not find the cause of the
problem, the car can be driven with a voltmeter
connected to a suspected circuit. An abnormal
voltage reading when the problem occurs
indicates the problem may be in that circuit. If
the wiring and connections check OK and a
trouble code was stored for a circuit having a
sensor, except for Codes 44 and 45, substitute a
known good sensor and recheck.
A "Scan" tool can also be used by selecting the
position of the suspected problem circuit and
moving related wiring and connectors. See
Introduction to this section on how each "Scan"
tool position can be used.
• An intermittent "Service Engine Soon" light
with no stored code may be caused by:
Ignition coil shorted to ground and arcing at
spark plug wires or plugs.
"Service Engine Soon" light wire to
electronic control module (ECM) shorted to
ground. (CKT 419).
- Diagnostic "Test" Terminal wire to ECM,
shorted to ground. (CKT 451)
ECM power grounds. See ECM wiring
diagrams.
« Loss of trouble code memory. To check,
disconnect throttle position sensor (TPS) and
idle engine until "Service Engine Soon" light
comes on. Code 22 should be stored, and kept in
memory when ignition is turned "OFF". If not,
the ECM is faulty.
• Check for an electrical system interference
caused by a defective relay, ECM driven
solenoid, or switch. They can cause a sharp
electrical surge. Normally, the problem will
occur when the faulty component is operated.
• Check for improper installation of electrical
options, such as lights, 2-way radios, etc.
• Electronic spark timing (EST) wires should be
kept away from spark plug wires, distributor
wires, distributor housing, coil, and generator.
Wire from CKT 453 to distributor should be a
good ground.
• Check for open diode across A/C compressor
clutch, and for other open diodes (see wiring
diagrams).