Diagnostic Aids

If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check the following conditions:

• Perform the Fuel Injector Coil Test. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS (GASOLINE) in SYSTEM & COMPONENT TESTING - TRUCKS article.
• An after-market vehicle theft deterrent system could cause a start then stall or a no-start condition.
• Fouled spark plugs.
• An Exhaust Gas Recirculation (EGR) valve stuck open.
• Water or foreign material in the fuel system.
• A grounded or intermittently grounded Ignition Control (IC) signal circuit.
• Restricted exhaust system.
• Check the following ignition components: A grounded tach circuit. Worn distributor cap. Worn distributor rotor. Check ignition wires by lightly spraying them with water in order to identify intermittent no-starts.
• Check the following mechanical components: Cylinder valve timing. Loose or broken timing chain. Low compression. Worn camshaft lobes. Bent or burned intake or exhaust valves.

The PCM has integrated circuits that are fault protected, therefore, if a circuit has failed, the integrated circuit may not be damaged. If that is the case, then the system will keep the circuit open until the condition has been corrected. Afterwards, reinstall the PCM and check the circuit. Replace the PCM only if the circuit is still inoperative. An intermittent may be caused by any of the following conditions: A poor connection. Rubbed through wire insulation. A broken wire inside the insulation. Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Repair as necessary.