4.0 Hard Start / Backfire / Rough Run after extended idle - Jeep Wrangler Forum

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Old 09-16-2009, 04:04 PM
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Join Date: Sep 2009
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biasdesign is on a distinguished road
4.0 Hard Start / Backfire / Rough Run after extended idle

Suddenly it takes 3-4 (sometimes 5, 6 or 7!) attempts to get it started.

It'll FINALLY sputter, sluggishly and with a rough deep idle, into starting.

Then completely runs fine.

Then, while at red lights, if I don't continually work the gas pedal, when I start to go, it sputters and runs VERY roughly for 10 -15 seconds, then back to 100% normal.

A couple of times, I've tried pumping the gas pedal a bunch (thinking it wasn't getting gas due to a bad pump) and then, when it finally starts - it backfires INCREDIBLY loudly, like a gun shot.

ANY ideas?

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Old 12-29-2009, 06:49 PM   #2
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pretty simular problem here - my 87 4.2l... just got it running 9 timing was off) we got it to idle perfect - but when you accelerate standing still, its a little hesitant but makes its way up the RPM's .. not sure what it is.. when you drive it ( vehicle weight and uphil) its really hard to do without it sputtering and farting up and down the street - but if you gently accelerate.. its ok - ...

i thought of timing chain, TPS, Fuel pump/filter...and - car issues -

any luck with yours - check out my thread - search for my thread by my name - anklenawer obvoiusly..

good luck
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