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Old 12-05-2011, 10:05 AM   #1
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Default Engine missfire code 0304 (fixed)

I have a 2002 bonneville SSei that is experiencing a miss fire on cylinder #4. I have replaced the plugs, wires, moved the coils around and replaced the icm. Still misses. any more ideas?
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Old 12-05-2011, 11:37 AM   #2
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Have you checked your injector? Check the path the plug wire takes. I've seen broken valve springs cause miss. Also try a compression test.
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Old 12-05-2011, 05:18 PM   #3
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Listen to the injector on cylinder 4 with a mechanics stethoscope (try a wooden dowel if you don't have a stethoscope) and compare the sound you hear to another injector. You should hear a steady ticking noise as the injector fires. If you don't hear it you need to check if the injector is getting a signal. The easiest way to do that is to take an automotive bulb that has wires on the end that can be straightened out and stuck in a connector. Pull the electrical connector off the injector on cylinder 4 and insert the bulb wires into the body side connector. Have someone crank the engine and see if the bulb is lighting in cadence with the RPM'*.

If you are getting signal, but don't hear the injector firing, replace the injector. If you are not getting signal you have a bigger problem.

You can also try switching injectors with another cylinder and see if the misfire moves to the other cylinder.

Misfires on a single cylinder can be a bad plug, a bad plug wire, a defective injector, or a mechanical issue. If you don't fix it with the plug, wire or injector, you can narrow down the mechanical issue by doing a compression test on the misfiring cylinder, and/or pull the valve cover and inspect for any damaged parts in the valve train.
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Old 12-06-2011, 11:55 PM   #4
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It turned out to be a bad seal on the injector. Runs fine now. Thanks for the input.
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Old 12-07-2011, 08:02 AM   #5
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Good to hear you found it.
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