Question about Jeep Cherokee

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Misses when cold start then runs ok. took it to 3 shops including the jeep dealer and no codes show. the outlet pressure fuel pump and filter is normal. the hesitation only happens when it is cold started but not everytime. none of the shops could replicate the problem.

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You may have a coolant or manifold temp sensor that is out of range enough to give you a slight problem but not bad enough to create a code. Check ohm readings: coolant sensor should read about 7,000 ohms cold and less than 1,000 ohms hot. Manifold sensor should read 4,000 ohms or less after it has warmed up and should decrease with any rise in temp.
Slight vacuum leaks can give you problems cold as well...check all hoses and fittings for loose fit or cracks. An injector with a slight leak can also flood one cylinder overnight, just enough to give a rough idle till it clears itself out.
Damp ignition parts (cap, rotor, wires and coil) can also give the same symptoms and that too may disappear after engine heat drys them up.
OK, I've thrown a lot at you but there are quite a number of things that can cause your problem. If the vehicle was in my shop, I'd need to check all of them and possibly more to find it. You need to go over everything carefully. Haynes and chilton list those tests and more and may also be helpful.(available in most larger parts stores)
good luck

Posted on Jan 31, 2010

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At this juncture, it could be nearly anything, including a low pressure delivery from the pump. Tell us more so we can help you better!

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2.5L or 4.0L? engine.
ever do a full service on this car , with a fuel filter.
or wrong gas cap, does car run ok cap off? or loose?
ignore cap off DTC errors. EVAP errors when done, ok?
start with basics.
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the filter is part of the top of pump at top of the FP reg. in tank.
that be how its done. no need to guess. at all.
in this case, the pressure test is after, the cap checks.
the wrong cap will have a missing, cap vacuum breaker this cause
the pump to fail (it cant suck in a hard vacuum at all, get a new cap)

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1 Answer

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