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Unread 02-24-2013, 02:37 PM   #1
JCarroll89
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4.0 Bucking and stalling after continuous driving

Hey guys, looking for a little advice here. She has no trouble starting or running from cold but after about 20-25 minutes of highway driving she starts sputtering, bucking and loses power. After I let it sit for a bit and she drops down below operating temperature she'll run for a little bit longer and then the same thing happens. Seeing as this seems to be related to the issue prone o2 sensors that's what I'm planning on atleast cleaning if not replacing but is there anything else I should try before that? Thanks, cheers

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Unread 02-24-2013, 02:43 PM   #2
JCarroll89
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No check engine light either
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Unread 02-25-2013, 11:29 AM   #3
Jonny Jeep
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I doubt it's O2 sensors. I'd suspect something overheating. Prime suspects would be crank sensor or coil. I've heard of pouring cold water over the crank sensor before to cool it down and get driving again sooner. It's only a temporary help though as once the crank sensor fails fully you'd be going nowhere. Overheating coils can cause the same sort of driving issues.

If you do suspect the O2 sensors, it's only the upstream one used for fuel mix. You can run with it disconnected, which may bring on the CEL and trip a code, and if the symptoms remain the O2 is not the problem.
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Unread 02-26-2013, 01:43 AM   #4
oakmckinley
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When my crank sensor went, it wouldn't bog down at all-just stall.

Not sure if a engine temp sensor would cause this? Could be off and the engine is trying to compensate for it not knowing its at temp.
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Unread 02-27-2013, 09:15 AM   #5
JCarroll89
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I don't think it's the temp sensor, she doesn't overheat at all and coolent is circulating when it opens. I put a new crank sensor in yesterday but haven't gotten to test it out yet. I'll let you know how it goes.
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Unread 02-27-2013, 01:11 PM   #6
oakmckinley
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There is more than one temp sensor.
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Unread 02-27-2013, 06:13 PM   #7
JCarroll89
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Well I replaced the crank sensor and o2 sensors but its still happining. After a cold start with no problems cranking, had no problems driving 5 miles down town on city streets, took it on the highway for about ten miles with no problem, took the same highway back and while on the off ramp it started bucking and cutting out. If I put it in neutral and coast to a stop it will idle rough and if I hit the gas while idleing it will maybe make it to two grand and then almost stall out. Turned it off let it sit for a few, started it back up, cranked fine (it has a hard time cranking if I try to start it right after turning it off after it bogs out) and only made it about 50 ft before buckin and boggin. It doesn't completely stall out if I let off the throttle and drop it in neutral as soon as I first notice it, and it idles fine once we get over to the shoulder as long as I stay off the throttle. After inching my way back home I just let it idle for about 10 minutes and my friend came over to ride along and see if he could figure it out, ran fine for 5 miles of city driving, not even a mile on the highway and it started ****tin the bed. After it starts, it will continue doing it. The longer it sits the further it makes it after starting it back up.
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Unread 02-27-2013, 06:46 PM   #8
FarmerinVA
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Have you replaced the spark plugs? I have this problem. Cleaning the throttle body, MAP, and IAC helped but did not solve it entirely, and OBDII shows no code issues. I was told on this forum that I should next try changing the plugs to Autolite XP985 plugs. I haven't done that yet (I'm not driving it this month, so I just haven't put them in yet), but I did look at one of my plugs and found that the gap, which was originally supposed to be 0.035 spec, has worn out of spec to about 0.050. The plug looked to be original, meaning it's got 120k miles on it (I'm the third owner).
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Unread 02-27-2013, 07:10 PM   #9
JCarroll89
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Just picked up 6 of them today and a new cap. Would one bad plug cause something like this though? It almost feels like once it starts acting up hitting on the throttle feels like its flooding the engine.
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Unread 02-27-2013, 07:15 PM   #10
FarmerinVA
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One bad plug could definitely cause it. It's basically a misfire. But my bet is that if I have one bad plug due to wear, I have several.
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My do-it-yourself install thread for a TrueTrac in the rear, upgraded shafts, and a PowerTrax No-Slip in the front:

http://www.jeepforum.com/forum/f9/ex...hafts-1234745/
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Unread 02-27-2013, 07:37 PM   #11
JCarroll89
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Ok, I'm gonna swap the plugs and cap, clean the MAP with some map cleaner and run it with the upstream o2 disconnected tonight
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Unread 02-27-2013, 07:43 PM   #12
JCarroll89
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Just out of curiosity, would a fuel pump issue cause something like this? I wouldn't think so since it has no problem cranking and runs like a champ through town
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Unread 02-27-2013, 08:02 PM   #13
karik
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had exactly the same problem. unfortunately i threw a lot of things at it at the same time to make the random stall and hard start go away. like you i never had a problem with a cold start, only a stall or hard start at normal operating temp. no MIL, no codes on the scanner.

replacing coil, replaced tps, cleaned throttle body and idle air control. took apart every connector, cleaned with contact cleaner and re-assembled with di-electric grease, shortened screws on PCM, swapped PCM. NO EFFECT ON STALL.

Here's the killer. Heard rubbing noise one morning when it was -30, sounded like rotor was rubbing inside the distributor, so figured i'd go to the scrap yard and grab a core for re-build. dissasembled core, cleaned everything, new cap, rotor, cam sensor (pickup). at the same time i bought a new crank sensor and upstream o2 sensor. put all that in and STALL GONE.

you've replaced crank sensor and o2 sensor, cam sensor is cheap and extremely easy to replace. take cap off, and it's right there under the rotor. worth a shot.

99 TJ with 4.0 and automatic.
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Unread 02-28-2013, 02:04 PM   #14
JCarroll89
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How did your distributor cap look when you took it off?
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Unread 02-28-2013, 04:02 PM   #15
karik
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hopefully the pics work, you can kinda make out the schmutz on the cam position sensor magnet.
thunder-bay-20130228-00633.jpg   thunder-bay-20130228-00632.jpg   thunder-bay-20130228-00634.jpg   thunder-bay-20130228-00635.jpg   thunder-bay-20130228-00636.jpg  

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