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Unread 08-04-2009, 02:56 PM   #1
sterlingmarlin3
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2000 WJ 
 
Join Date: Feb 2009
Location: canada
Posts: 4
4.0 hesitation, miss, after a few miles

starts up fine, 2 miles on the road it misses, hesitates, backfires then smoothes out works fine, if i shut it off and restart, hesitation is gone. new plugs, no codes, 270,000 any ideas?

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Unread 08-04-2009, 03:34 PM   #2
amonostereo
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1993 ZJ 
 
Join Date: Aug 2007
Location: Golden, CO
Posts: 334
did it start this after the new plugs went in, or was it this problem which prompted the new plugs?

does it do this at 2 miles every time you take it out? or is it just after a certain time running?
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'93 5.2L V8, Laredo, 242 TC swapped from a 249, 3" Coils up front and Front coils in the Rear, JKS Adjustable Track bar, K&N Cold Air Intake with Amsoil filter, Rear cargo area shelving, and KOR's Steering Gear Brace, IRO's Over-The-Knuckle Steering, Top Light Rail, Top Tire Carrier... for now...
OR If you prefer acronyms: 93 5.2 V8, 249>242, 3" FC, ~2" RC, JKS Adj. TB w/ KOR TB Bracket, K&N CIA w/ Amsoil filter, Shelves, KOR SB, IRO OTK HD steering
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Unread 08-04-2009, 03:50 PM   #3
newfieZJ
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1995 ZJ 
 
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It helps to know what you drive , fill out your info please

Sounds like the upsteam 02 sensor , if a 96 or newer
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Unread 08-04-2009, 05:05 PM   #4
SUfan
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1995 ZJ 
 
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Location: Syracuse, N.Y.
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It could be the egr valve. They tend to go bad after a while< just had the same problem with mine popping, missfire ect. changed it and it ran like new again.
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Unread 08-05-2009, 12:36 PM   #5
sterlingmarlin3
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it happens the same time each time about the 2 mile mark, warm or cold, platnum plugs were just routine, seems to happen more now
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Unread 08-06-2009, 04:12 PM   #6
newfieZJ
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Try unplugging the upstream (closest to the engine) 02 sensor . This will cause a engine light but does no damage if just doing the test . Drive it a few days . If the issue goes away , replace the senser with a Mopar unit . I'll describe the symptoms

Happens only within 3-5 minutes of starting , can be cold or warmed up .
Stumbling and backfiring lasts for approx 30-45 seconds , then , just clears up (backfiring most likely a result of trying to accelerate while this occurs)
Once finished it's little hissy fit , it will run all day without issue , provided it's not shut off .

If that's whats happening , skip the test , install sensor

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Unread 08-07-2009, 02:30 PM   #7
sterlingmarlin3
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thats exactly what its doing, many thanks
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