ZJ 6cyl runs bad after 15 minutes of driving? - JeepForum.com

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post #1 of 5 Old 08-02-2009, 02:19 AM Thread Starter
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1995 ZJ 
Join Date: Aug 2009
Location: Western Oregon
Posts: 3
ZJ 6cyl runs bad after 15 minutes of driving?

After chasing a bunch of little problems with my 95 ZJ 4.0 6 cyl that I just bought, the last engine issue eludes me....

The engine runs strong and clean when my jeep has been sitting for a while...until I drive it for 10-15 minutes, out of nowhere, starts to sputter and studder like mad. It is still driveable at this point, but runs horribly and makes awful noises (perhaps misfiring or bad fuel)

If I let it sit for a couple hours to cool back down, it will run perfect for another 10-15 minutes till it warms back up again. Im stuck, any suggestions on this?

No throwing any codes AFAIK, and I haven't been able to find anything like this searching the forums. Any related posts?

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post #2 of 5 Old 08-02-2009, 02:25 AM
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1998 ZJ 
Join Date: Apr 2009
Location: Morrison
Posts: 410
how many miles?
Seems like it is related to the engine going into closed mode once warm. Have you searched for 02 sensor symptoms?

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post #3 of 5 Old 08-02-2009, 02:44 AM Thread Starter
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1995 ZJ 
Join Date: Aug 2009
Location: Western Oregon
Posts: 3
155xxx miles.

Why symptoms should I look for in a bad O2 sensor?
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post #4 of 5 Old 08-02-2009, 04:17 AM
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1950 M-38 
Join Date: Aug 2009
Location: Key West
Posts: 44
You aren't really giving alot of information.

So after a while it starts misfiring and wanting to quit??? after you have driven it a while...could be a number of things. what it reminds me of is the fuel pump on a disco I had. So it could be your solenoid overheating and then not feeding enough gas to the car.

It could be a bad o2 sensor and is making different reading and causes you to run rich or lean and stutter.
Is your MAF clean?
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post #5 of 5 Old 08-02-2009, 02:45 PM
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1997 ZJ 
Join Date: Dec 2006
Posts: 19,793
disconnect the upstream o2 sensor and drive it around for a while. it will throw a code but if it doesn't do any of the symptoms you're experiencing you've found your bad part.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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