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Old 10-25-2010, 06:18 PM
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Stalling out and back firing through the exhaust..

Hello folk..Its been a while since I have been on here..LOL Just been really crazy busy........Anyway I have a problem that I am stumped on..My 97 4.0 TJ that now has a 99 4.0L engine has been running great since the engine and auto to stick swaps and even better after the regear but I now have a problem with the way its running.It will simply fall on its face from time to time in first and second gear..Not as bad once you get up to speed if you can..It jerks and bucks really wild in first..It does not do this every time but I would say about 80% of the time it does. I checked fuel pressure and it is around 50lb ,new plugs ,wires,cap and rotor button.Swapped out the IAC with a know good one.No help...I can get it to do it while sitting still and bringing the RPMs up to about 3K-4K and it will start spitting and sputtering and even back fires through the exhaust..Any ideas would be very much appreciated.............BTW the CEL does not work since the engine,trans,and wiring change....

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Old 10-25-2010, 06:57 PM   #2
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check the timing and make sure the plug wires are on the distributor in the correct locations. in my experience backfires are usually caused by timing issues in about 80% of the cases. The others are due to an overly rich mixture. When vehicles without a distributor exibit these symptoms its usually the crank or camshaft position sensors.

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Old 10-25-2010, 07:08 PM
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Quote:
Originally Posted by jgorm View Post
check the timing and make sure the plug wires are on the distributor in the correct locations. in my experience backfires are usually caused by timing issues in about 80% of the cases. The others are due to an overly rich mixture. When vehicles without a distributor exibit these symptoms its usually the crank or camshaft position sensors.
Yeah that has been my experiences as well but the distributor is tight and I know there wouldnt be enough slack to jump in and out of time with only 84K miles... It is strange...
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Old 11-01-2010, 11:02 AM
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wow not a lot of help on this one..I changed the TPS,the map sensor and the o2 sensor from the 97 but the IAC,crank and cam sensors were differernt so It has to be the IAC,crank or cam sensor I guess..First one in a long time I have to guess at..I hate it...
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Old 11-01-2010, 11:58 AM   #5
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How do the plugs look? And are they stock rather than "non-performance" gimmick plugs?
Sounds to me more like an ignition problem.
Tried swapping out the coil wire for another?

A chain doesn't "jump in and out."
An IAC only works a idle, not above - it's just an air bleed.
Usually the crank and cam position sensors affect it at all RPM, not just the narrow range.

"You said the CEL doesn't work since the engine change" -- why?

If no CEL, it's probably running very rich - plugs getting fouled.

Also check the TPS - key on, engine off - use an analog voltmeter on it - SLOWLY open the throttle while watching the center wire's voltage. Look for any intermittancy while the voltage sweeps. They get dirty or scratchy like an old radio's volume control.
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