ZJ 6cyl runs bad after 15 minutes of driving? - JeepForum.com
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Unread 08-02-2009, 03:19 AM   #1
jeepspotter
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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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Unread 08-02-2009, 03:25 AM   #2
kwellzz
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1998 ZJ 
 
Join Date: Apr 2009
Location: Morrison, CO
Posts: 366
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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Unread 08-02-2009, 03:44 AM   #3
jeepspotter
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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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Unread 08-02-2009, 05:17 AM   #4
sidescrollin
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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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Unread 08-02-2009, 03:45 PM   #5
ratmonkey
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1997 ZJ 
 
Join Date: Dec 2006
Location: , Pennsylvania
Posts: 19,794
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.
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