What could be causing my cylinder 1 misfire?

[Gareth Randall]

For about 3 years now, my 2005 Jeep Liberty 3.7L has had an intermittent misfire on cylinder 1. The plug and coil have been replaced twice, but still the problem recurs.

There’s no specific trigger that I can discern. One day the CEL will come on, I’ll pull the code and it’ll be P0300 and P0301. I’ll reset the code and the CEL will stay off for a while – last year, it stayed off for over 1500 miles of driving – but usually it’ll be back within about a week, which equates to about 200 miles.

I never actually notice the misfire, and the engine seems to be running as smoothly as it ever did, apart from a slightly lumpy idle (which may just be down to a dirty IAC motor – it’s never been cleaned since the Jeep was new). If I don’t bother to reset the code the CEL will eventually go off by itself, meaning the problem hasn’t recurred within the last 50 key cycles.

So… any suggestions of where to look? I’d like to nail this one permanently if possible, but obviously such an intermittent fault could well be extremely difficult to run to ground.

Topic

[college man]

A misfire could be fuel,spark or compression. A intake leak
can cause an issue also. check out this link for more info.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Lorrin Barth]

Since this is picked up by the computer so infrequently it makes me wonder if maybe the computer is a little too fussy. The computer doesn’t set a code with every misfire. If it did everyone would have codes all of the time. So, there is a threshold that has to be exceeded. Sometimes these thresholds need adjusting. So, the first thing I would suggest is checking with the dealership for any computer code updates.

[Author]

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