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 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or low speed.

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

IGNITION SYSTEM
Check for cylinder miss by:
1. Using injector balance test on Tech 1 listed under miscellaneous test menu or use Diagnostic Chart C-4. Testing and Inspection

Check for cylinder miss by:
1. Start engine, allow engine to stabilize then disconnect Idle Speed Control (ISC) motor. Remove one spark plug wire at a time, using insulated pliers.

CAUTION: Do Not perform this test for more than 2 minutes, as this test may cause damage to the three-way catalytic converters.

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 ISC motor.
3. If there is no RPM drop on one or more cylinders, or excessive variation in drop, check for spark on the suspected cylinder(s) using a shop oscilloscope or with J 26792 (ST 125) spark tester or equivalent. If no spark, refer to Chart A-3. 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:
Ignition wires by connecting ohmmeter to ends of each wire in question. If meter reads over 30,000 ohms, replace wire(s).

FUEL SYSTEM
Check:
Fuel system - Plugged fuel filter, low pressure. Use Chart A-7. Testing and Inspection
Contaminated fuel.
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. Testing and Inspection
Perform the injector balance test. Refer to Chart C-2A. Testing and Inspection

ENGINE MECHANICAL
Check:
Compression. Perform compression check on questionable cylinder(s). If compression is low, repair as necessary.
Base engine. Check for broken valve springs, worn camshaft lobes and valve timing, repair as necessary.

ADDITIONAL CHECKS
Check:
For electromagnetic interference. An engine miss can be caused by Electromagnetic Interference (EMI) on the reference circuit. Electromagnetic interference 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 change, indicates electromagnetic interference is present. If the problem exists, check routing of secondary wires, check ignition control module ground circuit.
Intake and exhaust manifold passage for casting flash.
For an intermittent, use DTC 41 camshaft position sensor circuit or DTC 25 crankshaft position sensor circuit.