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I have a 04 wj, 4.0, auto, 4wd. It always ran good. Recently, I took it for a test drive, & it shifted in less than 50 ft, then shifted again, & then after that,it seemed to lack power. My ses light was on for Map sensor. I changed map sensor. It didn't do anything different. It keeps stalling during idle. I put it in gear & it stalls instantly. So today o changed the tps, cause of the rough idle. It seemed to help, but not with the stalling. I restarted it after the sensor change & it stalled instantly. I couldn't even move. I had to gas it ,to make it move. I did try to test fuel pressure, but noticed o had no port on the fuel rail. I am going to change out the fuel.rail from my xj. I was wandering if it any of the following: low fuel pressure? Bad pressure regulator ? Bad cps ? Bad neutral safety switch. I do have the 42re from what I was told by the dealer. This jeep always ran great previously. Any help will be appreciated.
 

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Well I am not much use in diagnosing problems like this, but I CAN tell you the problem is not your neutral safety switch. The NSS is in the starting circuit and would prevent your starter from rolling; that is not your problem.

Is it throwing any codes? Check with a scanner or code reader. If you do not have one or cannot get to the parts store for a free scan, do the key dance* and write down any codes displayed on the odometer. (*key off-on x3) CKS or CPS problems should show up in a code.

Fuel pressure test sounds like a great idea, maybe you have a bad pump or clogged fuel filter. Maybe you need a thorough throttle body cleaning. Sometimes clogged catalytic converters stop up the exhaust and cause stalling.

Any other trouble lights stay lit up on the instrument panel? Security key maybe? Trouble with the SKIM can shut down the fuel pump.
 

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Stalling can be caused, even when idling, by a bad IAC valve. My 99 Jeep Grand Cherokee has got through two in the last six years, the second one recently installed which instantly solved the problem of stalling. BUT it took a high quality scanner to diagnose the problem. Had it scanned several times with cheaper ones which could not identify the failure of that valve. Then ran into a mechanic who had spent serious money on his scanner and it got the answer in seconds. Just sayin'...
 

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What was changed from when it ran good until the stalling started?
Maybe a vacuum hose came off or cracked? Does it run if you keep your foot on the gas?


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To be clear GMAN...We have had others post about their WIRING at the NSS that was shorted together. The insulation shrinks at the connector significantly, and then the wires touch each other. This had caused hard starting and weird driveablilty issues. But you are correct, in a NORMAL situation, the NSS would never come into a driveability concern. Might wanna double check this wiring in this case. I wonder about the exhaust being plugged...If it was plugged, the lack of exhaust getting out would fool with the map sensor, as it would cause very low engine vacumn. Maybe drop the exhaust at the manifolds and see if it runs better?
 

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Do you ever get water in your fuel in your part of the United States Bubba?
Or anything else that shouldn't be there?
 
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