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IGNITION
Troubleshooting
The ECM is designed such that if a sensor fails, the ECM will compensate so that the en-
gine does not go into an over-rich condition.
Disconnecting a sensor for troubleshooting purposes may have no noticeable effect.
Troubleshooting Without Digital Diagnostic Terminal
Troubleshooting without the DDT is limited to checking resistance on some of the sen-
sors.
Typical failures usually do not involve the ECM. Connectors, set-up, and mechanical wear
are most likely at fault.
Verify spark plug wires are securely installed (pushed in) into the coil tower.
The engine may not run or may not run above idle with the wrong spark plugs installed.
Swap ignition coils to see if the problem follows the coil or stays with the particular
cylinder.
NOTE: ECMs are capable of performing a cylinder misfire test to isolate problem cylin-
ders. Once a suspect cylinder is located, an output load test on the ignition coil, fuel injec-
tor and direct injector may be initiated through use of the DDT.
Any sensor or connection can be disconnected and reconnected while the engine is
operating without damaging the ECM. Disconnecting the crank position sensor will
stop the engine.
IMPORTANT: Any sensor that is disconnected while the engine is running will be
recorded as a Fault in the ECM Fault History. Use the DDT to view and clear the fault
history when troubleshooting/repair is completed.
If all cylinders exhibit similar symptoms, the problem is with a sensor or harness input
to the ECM.
If problem is speed related or intermittent, it is probably connector or contact related.
Inspect connectors for corrosion, loose wires or loose pins. Secure connector seating;
use dielectric compound 92-823506-1.
Inspect the harness for obvious damage: pinched wires, chaffing.
Secure grounds and all connections involving ring terminals (coat with Liquid Neo-
prene 92-25711--3).
Check fuel pump connections and fuel pump pressure.
Page 2A-28
90-883728 JULY 2001
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Table of Contents
Troubleshooting
