1. If DTCs P0301, P0302, P0303 and/or P0304 is set, check for:
A fuel injector that is clogged, leaking fuel or air.
An open or shorted fuel injector circuit.
A spark plug malfunction, fouling or carbon deposits.
An open or leaking spark plug wire.
A distributor malfunction.
Low engine compression.
Out of specification valve adjustment.
Repair as necessary. If no problems are found, go to step 2).
2. Start engine and listen for clicking sound at fuel injector for suspect cylinder. If injector clicks, go to next step. If injector does not click, check for open or short in harness between fuel injector and PCM. See WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, replace fuel injector, and recheck. If symptom or DTC is gone, replace original fuel injector. If DTC resets, substitute a known-good PCM and recheck. If symptom or DTC is gone, replace original PCM.
3. Check freeze frame data. Perform PCM reset procedure and clear freeze frame data (if present) and DTC. Exchange spark plug from suspect cylinder with one from another cylinder. Connect SCS service connector. Test drive vehicle several times in freeze frame data range. If there is no freeze frame data of misfiring, test drive vehicle under various conditions and try to duplicate malfunction. If DTC P0301, P0302, P0303 or P0304 does not reset, misfire is not detected at this time. If misfire follows spark plug to different cylinder, replace spark plug. If misfire remains in same cylinder, go to next step.
4. Exchange fuel injector from suspect cylinder with one from another cylinder. Let engine idle for 2 minutes. Test drive vehicle several times in freeze frame data range. If there is no freeze frame data of misfiring, test drive vehicle under various conditions and try to duplicate malfunction.
5. If DTC P0301, P0302, P0303 or P0304 does not reset, misfire condition is not detected at this time. Possible intermittent fuel injector connection. If misfire follows injector to another cylinder, replace faulty fuel injector. If misfire remains in same cylinder check cylinder leak down, engine compression and Crankshaft Position (CKP) sensor. Repair as necessary.
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Saturday, January 10th, 2009 AT 10:34 PM