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Unread 04-20-2011, 09:01 AM   #1
IBIUIRIKIE
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1993 ZJ 
 
Join Date: Mar 2011
Location: Davison, Mi
Posts: 16
ZJ limited warming up problem?

Alright guys Im to the end of my rope.. I have a 93 jeep grand cherokee with the 4.0. When i leave the jeep overnight and start it in the morning it runs very bad when warming up. I can start the jeep it runs fine till it just gets over 100 degrees and then it bucks and acts like its not getting fuel. the rpms will go down to like 200 and then back up to normal. and sometimes it backfires thru exhaust. When the jeep hits 140 degrees and up it seems to run fine, and then i can drive the jeep all day. I can shut it off wait a few hours and still drive fine. just when it is left for an extended period of time like overnight, thats when i seem to have the problem.

Here is what i have done so far. Fuel pump, fuel pump connector has been removed and wires solderd together. fuel pump relay, idle air control valve, MAP sensor, spark plugs (had platnium, i then removed them and put the champion coppers in), cap, rotor, plug wires, and ignition coil. Have changed the Air Temp sensor, and the Coolant temp sensor, Oxygen sensor also. checked all fuses, i have even disarmed the alarm just in case it was somthing to do with it. I also have looked at vacum lines and have found nothing cracked, and canister seems to be fine.

I have NOT changed the the Fuel presure regulator, or the TPS. these are my next to change.

Im hoping someone else has been having an issue and could maybe point me in the right direction.

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Unread 04-20-2011, 09:36 AM   #2
speedbucket
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i believe on the 5.2 there are 2 coolant sensors on the front base of the intake manifold. one controls the gauge and one gives feedback to the computer. not sure about the 4.0 but maybe you changed the wrong one?
have you checked all your wires at the computer for corrosion or anything loose?
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Unread 04-20-2011, 09:51 AM   #3
Myetball
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I had an identical problem with my 98 ZJ. Turned out when I changed the crank sensor I installed it a fraction of an inch too far away from the sensor ring. By loosening the reatining bolt and moving it closer to the sensor ring the problem went away.

Since it doesn't look like you've replaced the crank sensor, maybe now would be a good time to check into it and/or check the connectivity between the sensor and the PCM.

ASD relay is another possibility.

Search though this thread for alot of good information and additional links for possible solutions:

http://www.jeepforum.com/forum/f13/i...rokee-1112078/
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Unread 04-20-2011, 10:40 AM   #4
IBIUIRIKIE
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Yea i have looked for the other coolant temp sensor but dont see one. The one i changed was a two wire which I believe to be the one for the computer not the gauge.

Also I did change the Crankshaft sensor, i did it twice actually because i thought the first one was defective. Its a single bolt crankshaft sensor and there is no room for adjustment. Sorry i forgot the mention that, it was the first sensor i changed.

I have also swapped relays. Really stummped here. Maybe a TPS, i have not changed that. I get NO codes at all. any ideas would help. Thanks
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Unread 04-20-2011, 10:53 AM   #5
speedbucket
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Any chance of an objectors acting funny at a certain temp range?
* injector, dam Droid auto correct
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Unread 04-20-2011, 11:22 AM   #6
MaintMech
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The 4.0 has two Oxygen sensors. One on the exhaust manifold by the engine and the other by the cat. I feel that if you change one you should change the other.
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Unread 04-20-2011, 11:33 AM   #7
IBIUIRIKIE
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I checked for another oxygen sensor, do not see two, i only have one before the cat. 93 I believe only had one. and i am not sure about the injectors. After the morning issue of it spit and sputtering to the point that i can not drive it till it warms up. I can then drive where ever, and let the motor cool, and then drive away just fine. it just seems to be an issue when it sits over night.

Thanks for the ideas though i will check just to make sure.
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Unread 04-22-2011, 12:03 AM   #8
Jeepin2637
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Here's a good way to know
  • <<1995<< OBD1 (only one O2 senor before cat)
  • >>1996>> OBD2 (one O2 sensor befor and Meet DOT Emission Standard).
You only have one, get a mopar 02 Sensor. Hase the O2 sensor ever been changed?? If you already replaced it whats the brand??
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Unread 04-23-2011, 06:42 PM   #9
IBIUIRIKIE
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Yea i have already changed it. But it was not a mopar part. It was actually an AC Delco part. I know its not GM but at least it wasnt a autozone cheapy. But if it was the O2 i would think the jeep would act up everytime i started the jeep when it was cooled back down. i may be wrong. But i have know idea what else to look at. I just changed the TPS, just incase, I noticed when i cheacked the old one that at open throttle it would only read 3.8, never up to 4.8 volts, not sure if it is the problem.
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Unread 04-24-2011, 12:04 AM   #10
Jeepin2637
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Hmm, now I wonder if those have to be adjusted. On my laser it had to be adjusted by my dsm link. Hmm dunno what you could use to fix it for a jeep. I bet some on here know's the answer to that question. No need to spend more money on a misdiagnostic if it can save you in the long run.
Check it out because it's common problems on DSM's when you change them.
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