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  #1  
Old February 15th, 2005, 04:13
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misfire off-idle

I've got very steady spark at idle, & all of a sudden (haven't driven in a few days) I've got a random drop out of spark as measured at the coil wire w/ a spark checker. It's smooth until you get off idle and all through the throttle positions it has a wicked spark drop out. What would cause this?
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Old March 3rd, 2005, 21:31
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Re: misfire off-idle

Every body has had a least a few CPS issues, I've had a hundred
In my previous post I mentioned that the spark drops out, but in particular it was cylinders 2,3 & 4 & 5 that lose it above idle. These cylinders are opposing on the distributor cap, (3 & 4 and also 2 & 5) leading me to the conclusion that two of the three big windows on the flywheel that trigger the CPS weren't triggering, or the CPS couldn't pick them up. I took out the CPS & cleaned the nipple & put it back in. Wow, now I've got 2 & 5 back, & only 3 & 4 are dropping out at rpm's. Since I've spent more $$ on CPS's than tires in the past few years, I just shook my head & went to Napa for a replacement. I installed it, only to have the flywheel beat the nipple to death in a few revolutions of the engine. Wonderful. I pulled it out & compared it to the one I just replaced. The older one (used from a junkyard)had an egg shape to the inner hole to mount it to the bellhousing. This allowed just a slight bit of up & away adjustment. The Napa one didn't. I went to the Jeep dealer & talked to a super cool tech who said that there was a TSB on the CPS's long ago, now canceled, that told the tech to wallow out the hole so that you could place the nipple a little closer to the tone ring when things go pear shaped (british slang for crappy). I never noticed the wallow before, so I reinstalled it & sure enough, if I try to mount it lower toward the flexplate it will beat against it, but seemingly only once per engine revolution. The tech gave me (YES, GAVE ME FOR FREE) a new CPS he had lying around his station. He warned me about my aftermarket flywheel, which does have a bit of a wobble to it as viewed from below. I am afraid to mount my freebie w/o a genuine Jeep flexplate, so I am going to get one this weekend, most likely used, & hopefully not warped or cracked. After all this rambling, can anyone recommend a way to check for out of round on a flexplate, particulary up & down in relation to the CPS, as this would seemingly be the reason for the occasional smack to the CPS nipple?
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Old March 3rd, 2005, 21:40
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Re: misfire off-idle

Put a dial indicator on it and turn the engine by hand. If your pulling the trans to change the flywheel, it would be easy to do then. If the sensor is adjustable, there is a small sticky backed circle of cardboard that is used to set the gap on the sensor. Check the dealer, new sensors come with it already stuck on but we always stocked the gap guage also. Stick it on push the sensor in till it touches the flywheel. When you start the engine the guage is knocked away, and your gap is set correctly.
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Old March 3rd, 2005, 21:47
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Re: misfire off-idle

Sound advice, thank you. My fancy, shiny, new & free CPS doesn't have any provision for adjustment, so I assume that cardboard trick is not at all possible? It would make sense that if the CPS contacted the tone ring while spinning it would damage the delicate metal of the el-cheapo flexplate tone ring, never to run properly again. If I replace both flexplate & CPS I really hope this problem goes away...
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Old March 3rd, 2005, 22:41
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Re: misfire off-idle

Old Man, made some mention of OEM screws being necessary for proper function of the CPS. Canīt actually remember why they were important, just something I filed away (in the old brain) as usefull information. A search may turn up something.
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Old March 5th, 2005, 22:31
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Re: misfire off-idle

Jeep now runs great again. I pulled the aftermarket flexplate out & put one in from a junkyard '89 w/ 150k. The aftermarket flexplate's tone ring was about 1/4 inch larger in diameter than the Jeep flexplate, enough to contact the CPS nipple, so I learned not to buy any important or hard to get to parts that say "Hecho in Mexico". Thanks for the help again guys.
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