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 careful visual and physical checks as described in preliminary checks. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Preliminary Checks. Testing and Inspection

ADDITIONAL CHECKS
1. Check For Electromagnetic Interference (EMI). An ignition misfire can be caused by EMI on the reference circuit. EMI can usually be detected by monitoring engine RPM with a Tech 1 scan tool. A sudden increase in RPM with little change in actual engine RPM change indicates EMI is present. If the problem exists, check routing of spark plug wires and electronic Ignition Control (IC) ground circuit.
2. Check the intake and exhaust manifold passage for casting flash.

IGNITION SYSTEM
1. Check for a cylinder misfire.
a. Start engine allowing engine to stabilize then disconnect Idle Air Control (IAC) valve. 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 catalytic converter.

b. If there is an RPM drop on all cylinders (equal to within 50 RPM), Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Rough, Unstable, or Incorrect Idle, Stalling. Rough, Unstable, or Incorrect Idle, Stalling Reconnect IAC valve.
c. If there is no RPM drop on one or more cylinders or excessive variation in RPM drop, check for spark on the suspected cylinder(s) using a shop oscilloscope or with J 26792 (ST-125) spark tester or equivalent. If there is no spark, refer to Ignition System / Testing and Inspection for intermittent operation or miss. If there is a spark, remove spark plug(s) in these cylinders and check for:
^ Insulator cracks.
^ Wear.
^ Improper gap.
^ Burned electrodes.
^ Heavy deposits.
d. Check the spark plug wires by connecting ohmmeter to ends of each wire in question. If meter reads over 30,000 ohms, replace wire(s).

ENGINE MECHANICAL
1. Check the compression. Perform a compression check on questionable cylinder(s) found above. If the compression is low, repair as necessary.
2. Check internal engine. Remove the rocker covers. Check for bent pushrods, worn rocker arms, broken valve springs, worn camshaft lobes and valve timing. Repair as necessary.

FUEL SYSTEM
1. Check the scan tool for injector fault which could indicate one or more faulty injectors or wiring.
2. Check the fuel system for a plugged fuel filter or low pressure. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart A-7. Related Tests, Information and Procedures
3. Check for contaminated fuel.
4. Check the injector drivers. Disconnect all of the injector harness connectors. Connect the J 34730-2 injector test light or equivalent 6 volt test light between the harness terminals of each injector connector and note the light while cranking. If the test light fails to blink at any connector, it is a faulty injector drive circuit harness, connector, terminal or Powertrain Control Module (PCM).
5. Perform the fuel injector coil / balance test. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-2A. Chart C-2A Fuel Injector Balance Test