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Old 12-01-2012, 05:35 PM
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misfire in cylinder #1 on 99 gc limited w/ 4.7l

Ok so yesterday on my way to work I noticed my jeep was running pretty rough...soon enough the check engine light came on. I thought maybe it was an o2 sensor or something. On my way home I stopped and had it scanned and the only code showing was a misfire in cylinder #1. The guy at the shop suggested just giving it a tune up since it hasn't had the plugs changed in awhile. So today I changed all 8 plugs replaced with OEM coppers cleaned the TB and gave everything a once over. Start it up and drove it around a little and yes it does seem to be running better over all....but still misfiring, no check engine light though but I don't think I drove it long enough for it to come back on. What else can I look into? I believe I read somewhere that a bad crank sensor can cause misfires but not throw any codes. Is this true and could it be the culprit? Anyone have any ideas? Any help is greatly appreciated! This is my daily driver so I have to keep it running
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Old 12-01-2012, 07:13 PM
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Re: misfire in cylinder #1 on 99 gc limited w/ 4.7l

::UPDATE::

So I took a long drive probably about an hour or so with stops in between at idle and still no check engine but still feels like a slight misfire. Could it possible have to do with the ECU adjusting itself after compensating for the misfiring cylinder? I know when I drove volkswagens (only cars I ever worked on so jeeps are new to me) sometimes it would take a few days for everything to run kosher again after a tune up. Would same go for jeeps?
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Old 12-01-2012, 07:42 PM
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Re: misfire in cylinder #1 on 99 gc limited w/ 4.7l

A misfire can be caused by several things. The 2 basics are fuel and spark, either one missing or not at the right time can cause a misfire.
So could have to do with ignition coil, fuel injector and sometimes also a crank sensor or cam sensor. You could swap the ignition coil with an other, but since you don't get the check engine light at the moment, it probably won't tell you anything.
The PCM should normally react instandly on changes, otherwise it would be difficult to regulate the engine. So i won't expect any changes after a while.
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Old 12-01-2012, 08:58 PM
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Re: misfire in cylinder #1 on 99 gc limited w/ 4.7l

Thanks for the post. I'll mess around with it a little more and see if anything changes. All the coils seemed to be in decent shape when I did the plugs, but there might be some internal issue with one of them. I can definitely tell it's on the drivers side so maybe I'll try swapping with one from the passenger side and see if there's a difference and try going from there.
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