Cuts Out/Misses

DEFINITION
Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust has a steady spitting sound at idle or low speed.

PRELIMINARY CHECKS
^ Perform the careful visual / physical checks as described in Preliminary Checks.

IGNITION SYSTEM
^ Check for cylinder miss by:

1. Starting engine, allow engine to stabilize then disconnect Idle Air Control (IAC) motor Using the Tech 1 injector balance test, shut "OFF" one injector connector at a time.
2. If there is an RPM drop on all cylinders (equal to within 50 RPM), refer to "Rough, Unstable, or Incorrect Idle, Stalling". Reconnect IAC valve.
3. If there is no RPM drop on one or more cylinders, or excessive variation is drop, check for spark on the suspected cylinder(s) using a J 26792 (ST 125) spark tester or equivalent.
4. If there is no spark, refer to Procedures / Diagnostic Charts / C Charts / Distributor Ignition System Check. Testing and Inspection
If there is a spark, remove spark plug(s) in these cylinders and check for:

- Insulator cracks.
- Wear.
- Improper gap.
- Burned electrodes.
- Heavy deposits.

^ Check spark plug wires by connecting ohmmeter to ends of each wire in question. If meter reads over 30,000 ohms, replace wire(s).
^ With engine running, spray coils and plug wires with fine water mist to check for faulty wires or coils.
Check sparkplug wires and/or connection for possible symptom that will cause a miss under various loads or light acceleration.

FUEL SYSTEM
^ Check fuel pressure, refer to Procedures / Diagnostic Charts / Chart A-6 Fuel System Diagnosis. Testing and Inspection
Check for contaminated fuel or restricted fuel filter.

ENGINE MECHANICAL
^ Check the compression. Perform compression check on questionable cylinder(s) found above. If compression is low, repair as necessary.
^ Check base engine. Remove rocker covers. Check for bent pushrods, worn rocker arms, broken valve springs, worn or broken camshaft lobes and incorrect valve timing. Repair as necessary.
^ Check intake and exhaust manifold passages for casting flash.