Chart C-4B Misfire Check

Chart C-4B: Misfire Check:

Ignition System Circuit:

CIRCUIT DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. By performing CHART C-2A first all injectors must be operating OK at this point. This chart covers ignition system related misfire only.Chart C-2A Injector Coil Test Procedure
2. A thorough visual/physical check of the engine components which typically may cause a misfire may eliminate the need for further diagnostics. Use fuel pressure gage J 34730-1. Check fuel pressure. Pressure after ignition "ON" should be (283-325 kPa) 41-47 psi. If fuel pressure is not within specification perform "Fuel System Check," CHART A-7. Related Tests, Information and Procedures
3. A spark tester such as a ST-125 must be used because it is essential to verify adequate available secondary voltage at the spark plug. (25,000 volts.) This simulates a "load" condition.
4. With engine running, try to induce the misfire by moving related harness connectors. This may help locate an intermittent connection.
5. If spark plugs check OK a mechanical engine problem may be causing misfire (i.e. worn camshaft, bent pushrod, low compression, etc.). Refer to ENGINE.

DIAGNOSTIC AIDS
The distributor vent system should also be checked. A blocked air supply to the distributor will cause vacuum to build within the distributor causing misfire. Refer to DISTRIBUTOR for vent system check procedure.