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Old 06-21-2014, 08:39 PM
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TJ stalls when Warm

1998 TJ 4.0 Automatic

Started after I pulled tranny to fix some leaks. Reinstalled and all was good, shifted good, good power, good response.
Drove about 40 miles out of town, dirt road about 10 miles hit uphill slopes, was in 4 hi, the steeper it got the less power i had, like no low end torque, put in 4 low, could barely make it over a small boulder. Eventually i had throttle pinned with zero power. Stopped and found exhaust leak, jeep stalled while idling, but would fire right back up. Turned around and went back home with no issues.

Problem has gotten worse, Jeep stalls when warm. I've done the following:

New exhaust pipes and new catalytic converter.
New 02 sensors, post and pre cat
New CPS mopar
New TPS mopar
New TPS connector and wiring
New IAC
New engine temp sensor
New distributor cap
New Rotor
Traced all wires and connectors from the gas tank all the way up into the engine, cleaned all.
Removed, cleaned, wire brushed to a shine all grounds.
Cleaned battery posts
Cleaned fuse box connections
Checked all fuses
Cleaned MAP sensor connector
Cleaned PCM connections, did wiggle test, backed off screws
Cleaned fuel injector connections
And I know im forgetting other things i've done.

So, start jeep cold, fires right up, idles real nice, will idle for 10 min or so, while its doing that i wiggle everything, no change, spray carb cleaner, no change, step on throttle, nice response, idles back down normal.

After warm it will hesitate, bog down, and stall. Sometimes you can hear it sucking for air befor it stalls, sometimes it will fix itself and idle high for a sec then drop down and eventually stall. If its doing this and i step on gas it will hesitate, bog and either stall or rev up, if i play with it it will go back to nice idle but eventually stall, if i keep playing with throttle it will start to backfire.

Any Ideas????

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Old 06-21-2014, 08:47 PM   #2
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How is the wiring going to your upstream 02 sensor? I know you replaced that 02 sensor but the symptoms sure sound like they could be upstream 02 sensor related. The computer only starts looking at the 02 sensor output once the engine warms up.

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Old 06-21-2014, 08:56 PM   #3
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Definitely sounds like it's the exhaust system related.
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Old 06-21-2014, 09:08 PM
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I havnt checked that wire, i will now. Yeah it sounds like its related, i know the engine pretty much runs on its own util warm, then the computer starts doing its readings and adjusting. Only stalls in closed loop.

I replaced the plug wires and plugs about a year ago, perhaps i got some bad ones. I heard the jeeps are pretty particular on what kind of plugs etc. Could bad plugs cause my issue? I would think it would act up warm or cold if they were bad. Maybe im wrong?
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Old 06-21-2014, 09:15 PM
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Wires to upstream look good, no cracks or frays.
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Old 06-21-2014, 09:18 PM   #6
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Older TJs like yours with a distributor aren't especially fussy about their spark plugs like the newer TJs without distributors are. Bosch plugs don't work all that well but they wouldn't cause that problem.
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Old 06-21-2014, 09:22 PM
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Dont know if this is true, i read somewhere that when replacing both 02 sensors you must do the following, because your computer is used to the old ones and will adjust performance negatively based on the old 02 sensors.

Disconnect both sensors, start jeep and alow it to go into closed loop, the computer will search for the 02 sensor feedback and will obtain none, then shut off jeep and disconnect battery, leaving sensors unplugged for 12 hours. Then reinstall sensors and reconnect battery.

This info was on a post with a guy that had a stalling issue, he said after doing this he had no more stalling.

Sounds far fetched, make sense to anyone?
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Old 06-21-2014, 09:40 PM   #8
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Weak fuel pump? Have seen it happen to two of my wheelin buddies. One is a 2.5 auto and the other a 4.0 auto. Would recommend checking fuel pressure.
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Old 06-21-2014, 09:46 PM
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Weak fuel pump, i thought about this, but i put it on the back of the list because i get plenty of fuel on start up and for a while after. I can step on the gas and it will rev good and strong, hold it down and its good, no hesitation at all. Its only after engine is good and hot. Are these symptoms similar to your buddy's or did they have fuel issues cold, warm or hot?
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Old 06-21-2014, 09:47 PM   #10
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The fuel pump suggestion is sounding very good about now.
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Old 06-21-2014, 09:56 PM
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I will definitely check fuel pressure, but does anyone know if fuel pressure or pump can be affected by the engine being warm only and not cold?
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Old 06-21-2014, 10:08 PM   #12
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For both of my friends that had failures, it was with the engine warm. On the 4.0, he was actually able to drive it but he had to bleed some fuel off of the rail into a bottle and pour into the t-body to get it started, then was able to nurse it home.
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Old 06-21-2014, 10:14 PM
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Thanks, looks like ill be dropping the tank. I only had a couple more options, plugs and wires or fuel pump... After That maybe blow her up haha.
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Old 11-26-2018, 04:16 PM   #14
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Having the same issue. What did you figure out for the fix?

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