Chart C-5, Electronic Spark Control
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This is an ESC functional test. Simulating engine knock by tapping on the engine block should cause a drop in RPM (decrease in timing). If RPM doesn't drop, either timing is not retarding or is retarded all the time.
- This should cause timing to fully retard by dropping voltage at ECM terminal "L". Retarding timing should cause RPM to drop.
- Normally voltage should be .08 volt AC, or more for a good knock sensor circuit.
- "SERVICE ENGINE SOON" light should be on and a Code 43 set because ESC system was retarded too long. If no light comes on, ECM is not retarding the spark because of voltage present on circuit No. 457 to terminal "L" or ECM is faulty.
- This tests if knock sensor is reason for retard signal. If engine knock is not present and timing increases when knock sensor is disconnected, faulty knock sensor is the cause.
- This tests if retard signal is due to "noise" on signal wire or a faulty controller. If timing increases when wire is disconnected from controller, fault is due to knock sensor signal wire running too close to an ignition or charging system wire. Reroute wire to correct.