Intermittent random misfire (P0300) - any ideas? -
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post #1 of 2 Old 06-14-2013, 12:34 PM Thread Starter
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2002 WJ 
Join Date: Apr 2007
Location: UK
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Intermittent random misfire (P0300) - any ideas?

My 2005 KJ has new plugs and coils and a new battery. Once every couple of weeks I'll get a CEL for the P0300 random misfire code. I'll reset it, and everything will be fine for another couple of weeks, and then it'll be back again. I'm not actually aware of the engine misfiring, and since the P0300 refers to multiple cylinders, I figured I *would* notice.

Any suggestions for things to check *other than* plugs, coils and battery? Could it possibly be the camshaft sensor (or similar) going bad? All the engine sensors are the 2005 factory originals, bar the O2 sensors, which have been changed once.

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post #2 of 2 Old 06-14-2013, 08:01 PM
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2004 TJ Wrangler 
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Misfires can ALSO be caused by faulty wiring to the coil, clogged/faulty fuel injectors, coolant leaks into the cylinder, bad fuel, low fuel pressure, carbon buildup and a faulty ECM. Based on my understanding, the P0300 is a generic fault that does NOT identify the exact cylinder or cylinders that are the problem. It does not necessarily mean more than 1 cylinder is misfiring. You will need to get a hold of a scan tool that can provide you the specific cylinder misfire otherwise youll be throwing parts at all the cylinders. There are a boat load of diagnostics that can be performed to identify the source or at least eliminate some of the causes.
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