Cuts Out/Misses

DEFINITION
Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases, not normally felt above 1500 RPM or km/h (30 mph). 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. Start 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), go to "Rough, Unstable, or Incorrect Idle, Stalling" symptom. 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. If no spark refer to Chart C-4 Misfire Diagnosis. 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 system - Plugged fuel filter, low pressure. Use Chart A-7. Testing and Inspection
Check for contaminated fuel.
Check injector drivers. Disconnect all injector harness connectors. Connect J 34730-2 Injector Test Light or equivalent 6 volts test light between the harness terminal, of each injector connector and note light while cranking. If test light fails to blink at any connector, refer to Chart A-3 (Part 2 of 3). Testing and Inspection
Perform the injector balance test. Refer to Chart C-2A. Testing and Inspection


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.

ADDITIONAL CHECKS
- Check for EMI interference. A missing condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a Tech 1. A sudden increase in displayed RPM with little change in actual engine RPM indicates EMI is present.
If the problem exists, check routing of secondary wires, check ignition control module ground circuit.
- Check the intake and exhaust manifold passage for casting flash.
- Check for an intermittent camshaft position sensor or crankshaft position sensor fault by monitoring "Cam Signal Error" on the Tech 1 data list; "Cam Signal Error" will increase to above 2 counts while the engine is running if a fault exists. Use DTC P0341 chart for diagnosis of a "Cam Signal Error" fault. Testing and Inspection
- Check for a bent or missing vane on the crankshaft balancer interrupter rings.
- Check the EGR system. Use Chart C-7, Exhaust Gas Recirculation (EGR) Flow Check. Testing and Inspection