System Diagnosis - DIS (EST) Ignition System

TEST DESCRIPTION
An open or ground in the Electronic Spark Timing (EST) or bypass circuits will set a Code 42 and cause the engine to run on the ignition module timing. The ECM uses information from the speed density system and coolant sensors in addition to RPM to calculate spark advance as follows:

^ Cold engine = more spark advance
^ Engine under minimum load based on RPM and low amount of air flow = more spark advance
^ Hot engine = less spark advance
^ Engine under heavy load based on RPM and high air flow = less spark advance
^ If the engine cranks but will not run or immediately stalls, Chart A4-3 must be used to determine if the failure is in the "DIS" system or the fuel system. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart A4-3. Testing and Inspection

Code 42
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, Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-4F. Testing and Inspection

Code 12
Code 12 is used during the diagnostic circuit check procedure to test the diagnostic and code display ability of the Electronic Control Module (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.