Before beginning any diagnosis and testing procedures, visually inspect the components of the ignition system and check for the following:
Check the spark plug wires and boots for signs of poor insulation that could cause cross firing. 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.
You will need a good quality digital volt-ohmmeter and a spark tester to check the ignition system. A spark tester resembles a spark plug without threads and the side electrode removed. Do not attempt to use a modified spark plug.
SECONDARY SPARK TEST
When it is suspected that a spark plug may not be firing, the simplest test consists of a visual inspection as noted above. If no loose or damaged wires can be found, each coil-to-plug wire should be checked for spark.
- Twist the boot of the spark plug wire to loosen it, then carefully pull upwards and disconnect the wire from the plug.
- Connect the spark plug wire to Spark Tester tool SA9199Z or equivalent.
- Connect the spark tester to a suitable engine ground.
- Crank the engine and watch for a strong spark across the tester gap.
- If the spark is missing or weak, check the resistance of the coil-to-plug wire; it should be less than 12,000 ohms. Replace any wire with too high a resistance and repeat the test. If the wire resistance is good, but the spark is missing or weak, proceed to the DIS MODULE SPARK TEST.
- If no spark can be found for all of the wires, proceed to the NO SPARK TEST.
NO SPARK TEST
See Figures 1 and 2
If no spark can be found at any spark plug or coil, you must first determine if a cranking rpm signal is present from the Crankshaft Position Sensor (CPS). This can be accomplished in various ways:
Connect a scan tool as described in Emission Controls and watch for a CPS signal as the engine is cranked.
- If it has been determined that cranking rpm is present, proceed as follows:
- If it has been determined that no cranking rpm is present, proceed as follows: