Before beginning any diagnosis and testing procedures, visually inspect the components of the ignition system and engine control systems. Check for the following:
Check the spark plug wires and boots for signs of poor insulation that could cause crossfiring. Make sure the battery is fully charged and that all accessories are off during diagnosis and testing. Make sure the idle speed is within specification.
If an open or ground in the Ignition Control (IC) circuit occurs during engine operation, then engine will continue to run, but using a back-up timing mode (controlled by the ICM) based on preset timing values. The Malfunction Indicator Lamp (MIL) or SERVICE ENGINE SOON light will not illuminate at the first appearance of a break in the circuit. However, if the IC fault is still present once the engine is restarted, a Code 42 will set on OBD 1 systems in the PCM and the MIL will illuminate. Poor performance and fuel economy may be noticed while the engine is running under back-up timing.
When attempting to search for ignition troubles, keep in mind the various sensor inputs which the PCM uses to calculate timing may affect engine performance. The PCM will alter timing based on sensor inputs as follows:
With this in mind, DETONATION could be caused by low MAP output or high resistance in the coolant sensor circuit. POOR PERFORMANCE could be caused by a high MAP output or low resistance in the coolant sensor circuit.
Cylinder Drop Test
The cylinder drop test is performed when an engine misfire is evident. This test helps determine which cylinder is not contributing the proper power. The easiest way to perform this test is to remove the plug wires one at a time from the cylinders with the engine running.
- Place the transaxle in P , engage the emergency brake, and start the engine and let it idle.
Using a spark plug wire removing tool, preferably, the plier type, carefully remove the boot from one of the cylinders.
WARNINGMake sure your body is free from touching any part of the car which is metal. The secondary voltage in the ignition system is high and although it cannot kill you, it will shock you and it does hurt.
The engine will sputter, run worse, and possibly nearly stall. If this happens reinstall the plug wire and move to the next cylinder. If the engine runs no differently, or the difference is minimal, shut the engine off and inspect the spark plug wire, spark plug, and if necessary, perform component diagnostics as covered in this section. Perform the test on all cylinders to verify the which cylinders are suspect.
Secondary Spark Test
The best way to perform this procedure is to use a spark tester (available at most automotive parts stores). Three types of spark testers are commonly available. The Neon Bulb type is connected to the spark plug wire and flashes with each ignition pulse. The Air Gap type must be adjusted to the individual spark plug gap specified for the engine. The last type of spark plug tester looks like a spark plug with a grounding clip on the side, but there is no side electrode for the spark to jump to. The last two types of testers allows the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong).
- Disconnect a spark plug wire at the spark plug end.
- Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.
- Crank the engine and check for spark at the tester.
- If spark exists at the tester, the ignition system is functioning properly.
If spark does not exist at the spark plug wire, perform diagnosis of the ignition system using individual component diagnosis procedures.