Cuts Out, Misses

Definition: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases, not normally felt above 1500 revolution per minute or 48 kph (30 mile per hour). The exhaust has a steady spitting sound at idle or low speed.


PRELIMINARY CHECKS

^ Perform the careful visual/physical checks as described at start of "Symptoms,".


IGNITION SYSTEM

^ Check for cylinder miss by:

1. Start engine, allow engine to stabilize then disconnect idle air control 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 converter.

2. If there is a revolution per minute drop on all cylinders (equal to within 50 revolution per minute), go to "Rough, Unstable, or Incorrect Idle, Stalling" symptom. Reconnect idle air control valve.

3. If there is no revolution per minute (rpm) drop on one or more cylinders, or excessive variation is 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 for intermittent operation of 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.

^ CHECK: Spark plug 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.

^ CHECK: 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, it is a faulty injector drive circuit harness, connector or terminal.

ENGINE MECHANICAL

^ CHECK: Compression. Perform compression check on questionable cylinder(s) found above. If compression is low, repair as necessary.

^ CHECK: Engine parts. Remove cam covers. Check for broken valve springs, worn camshaft lobes and valve timing. Repair as necessary.

ADDITIONAL CHECKS

^ CHECK: For electromagnetic interference (EMI). A missing condition can be caused by EMI on the reference circuit. EMI can usually be detected by monitoring engine speed with a "Scan tool". A sudden increase in rpm with little change in actual engine speed change, indicates EMI is present. If the problem exists, check routing of secondary wires, check distributor ground circuit.

^ CHECK: Intake and exhaust manifold passage for casting flash.