Cuts Out/Misses

SYMPTOM DESCRIPTION:
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.



SYSTEM OR COMPONENT TO CHECK

IGNITION

CHECK:

CYLINDER MISFIRE

Start engine, allow engine to warm-up. Ground one spark plug wire at a time. If there is an rpm drop, on all cylinders, (equal to within 50 rpm), go to STALLS, ROUGH, UNSTABLE OR INCORRECT IDLE

NOTE: On vehicles with computer idle speed control, it is necessary to disable or fix the idle speed control so that the computer does not compensate for rpm drop when a cylinder is cancelled. Refer to Computers and Control Systems.

CAUTION: Do not perform this test for more than 2 minutes, as this may cause damage to the catalytic converter.

If there is no rpm drop on specific cylinders, or if there is an excessive variation in drop, check for poor spark on the suspected cylinders (those where there was little or no difference in engine speed when spark plug wire was grounded). If there is no spark, check the wire, distributor cap, and rotor for arcing or shorts. If there is a spark, remove the spark plug(s) in the suspect cylinders and check for heavy deposits, cracked insulators, burned electrodes etc. If no ignition problems are found, perform compression test. Compression should not vary by more than approx. 15% from highest to lowest. If it does, check the low cylinders for blown head gasket, burned valves or worn piston rings. If still no problems have been found, check for vacuum leaks, or plugged injector on the suspected cylinders.




FUEL

CHECK

- FUEL PRESSURE: Fuel pump delivery pressure and volume.
- FUEL INJECTOR: Poor spray pattern, clogged, or stuck injector.
- FUEL DISTRIBUTOR: Stuck or sluggish control plunger, plugged metering slits, mini filter in fuel inlet banjo bolt plugged or restricted.
- FUEL PRESSURE REGULATOR: System pressure too high or too low.
- FUEL QUALITY: Contaminated fuel or incorrect octane rating.




ENGINE

CHECK:

- COMPRESSION: Perform a compression check and cylinder leak down test. Look for low compression, sticking or leaking valves, cylinder head gasket burned out between adjacent cylinders or blown into coolant passages.
- VALVE TIMING: Remove rocker covers, inspect for worn rocker arms, weak valve springs or worn cam shaft lobes
- RESTRICTIONS: Intake and exhaust system casting flash, damaged tubing, or other restrictions.