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Old January 12th, 2021, 12:46
ntcampana ntcampana is offline
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Unhappy Please help - Near daily stalling immediately after startup

Hello, I have been trying to deal with this intermittent problem since September, and recently the problem is starting to happen almost on a daily basis and is quite literally ruining my life. Sorry if this post is kind of long, I just want to include as much relevant information as possible as even mechanics have been unable to diagnose this problem.

1991 Cherokee Limited 4.0 4x4 Automatic

The problem: Intermittent crank and start then stall. Engine will start like normal then cut off after .5 seconds, before it has a chance to actually idle. At first pressing the gas had no effect as it started. Within the past couple days, if I press the gas pedal the RPM's have started to rev a little higher before cutting off. Using a wire to jump the fuel pump relay also doesn't help. Problem goes away after waiting a few hours or so. Recently this has become an almost daily occurrence

Things I have done to fix this problem: New fuel pump ballast resistor, new ignition coil, 4 different crank position sensors (including mopar), new throttle position sensor, cleaned iac valve, new duralast gold battery, cleaned engine grounds, bosch 4 point injectors (4000 miles ago), spark plugs rotor and distributor cap 9000 miles ago

One morning back in September I woke up and tried to start the Jeep up to drive to work. I turned the key and the engine started up like normal, but before the RPMs even had a chance to stabilize after startup, the engine just cut off as if someone removed the key. Trying to start it again will result in either the starter cranking forever, or the engine starting and stalling again (about a 50/50 split between just cranking and start/stall). After 30 minutes of trying to get the Jeep started I decided to call AAA to get a tow back home. After doing some searching I became convinced that the crankshaft position sensor was the culprit, so I bought one from Autozone which seemed to solve the problem. It was probably 2 or 3 weeks before this problem came back, at which point I get the cps replaced for free under warranty. Some time later the problem came back again, so I bought a new old stock Mopar cps on ebay and still the problem came back.

Then I became convinced that the problem was with the fuel pump, but the pressure at the pump and the rail were good, and I can hear it prime every time I turn the key. The Jeep will also start and drive normally whenever the problem is not happening, although sometimes in the morning you have to keep the key twisted a little longer and press the gas a little bit. I even went offroading for the first time in the desert on New Years Day for 6 hours without shutting the engine off due to fear of it not starting back up again, and it performed beautifully. For this reason I don't think it is a problem with the fuel pump, but what do I know.

Last week the problem came back while I was at the beach and I had it towed to a mechanic. Of course they were closing by the time the Jeep got to them, and by the time they got a chance to look at it in the morning the problem went away again, only to come back the same night I got it back from the mechanic. Mechanic said every time the tried to start it it started right up, all the sensor had the proper readings and he couldn't find anything wrong with the wiring harness. I desperately need help with this as my Jeep is currently my only source of income as I do grocery delivery work with it.

Someone sent me a video by Bleepin Jeep on YouTube in which he has an XJ that is experiencing the exact same problem as mine. In the video he replaces the fuel pump ballast resistor which made me super hopeful that a new ballast resistor would solve the problem, but it did not. Here's a link to that video in case you want to watch it, it has a perfect representation of my problem
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Old January 12th, 2021, 13:01
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Anak Anak is offline
Join Date: Sep 2013
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Re: Please help - Near daily stalling immediately after startup

A couple of things come to mind...

Yes, I see the shop can't find anything wrong with the wiring harness, but that is like looking for a needle in a haystack. I advise you to follow the wiring for your O2 sensor (I expect you have just one, up near the collector for the header). Trace that from the O2 sensor up to where it departs from the main harness (probably somewhere in the vicinity of the front of the valve cover). Make sure that wire cannot contact the exhaust in any way. If it grounds out it will kill the engine. Hot exhaust will melt the insulation and ground it out, but when the exhaust cools it can lose that ground connection and run again. While I would expect a shop to catch that I would still check it myself. It is simple enough to do.

The next thing is the condition of your grounds. I went through a similar experience to yours. This is my account of that:

Best of luck and let us know how you get it resolved.
Project "Scope Creep": 1996 4wd 4.0L, AX15

The "Varmint-Mobile": 1997 ZJ Laredo, 4wd, 4.0L, Slushbox
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Old January 15th, 2021, 11:35
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8Mud 8Mud is offline
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Re: Please help - Near daily stalling immediately after startup

Ballast resistor, jump it and see what happens.
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