1999 Jeep Laredo coil pack problem?

1999 JEEP GRAND CHEROKEE LAREDO
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SD1455
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Engine Performance problem
1999 Jeep Laredo 6 cyl Four Wheel Drive Automatic 150k miles

got #1 misfire code Had code cleared and tune up done at shop. Ran good for a week. Drove in rain and check engine on again. #4 misfire code. now runs rough with sputtering 45-55 mph. no power uphill. coil pack not changed at tuneup. wondering if this could be problem
Oct 27, 2009 at 5:20 PM
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MHPAUTOS
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HI there,

Could well be a faulty coil, you can test with a multi meter but often they do test ok and start to break down when they heat up, a run on an oscilloscope can help track down faulty coils.

mark (mhpautos)
Oct 27, 2009 at 7:00 PM
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SD1455
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disconnected battery to clear codes. Changed coil packs . seems to run a little better still sputters @ 45-55 mph No engine codes come up. Read somewhere that car may have to "relearn" shifting after disconnect. How long does that usually take
Oct 28, 2009 at 5:14 PM
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MHPAUTOS
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HI there,

I would have to check this for your car, but normally any re learn will take place after a few drive cycles, i will look into it for you, but it will take a few days as i am away no a training course as of this after noon for a few day.

Mark
Oct 28, 2009 at 5:21 PM
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SD1455
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still idles rough. came to a stop and it stalled. drove some more and got #4 misfire code. new plugs ,coil packs,fuel filter, o2 sensor. maybe bad injector?
Oct 28, 2009 at 10:43 PM
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MHPAUTOS
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Could be, but i would be checking for a vacuum leak as well, i could not imagine all 4 injectors going at once, have you checked for bad fuel?

Mark
Oct 28, 2009 at 11:07 PM
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SD1455
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havent found any vacuum leaks
Oct 28, 2009 at 11:12 PM
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SD1455
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brought back to shop. found 4 of the 6 plugs with cracks in ceramic. changed plugs and runs good again. hopefully more than a week this time. thanks for the replies
Oct 29, 2009 at 5:02 PM
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SD1455
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takes 3 times to start in morning. stalled twice yesterday when at a stop.
Nov 3, 2009 at 11:24 AM