Mopar MPI rough running issue -
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post #1 of 7 Old 09-03-2013, 08:35 AM Thread Starter
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1982 CJ7 
Join Date: Jul 2013
Location: Vershire
Posts: 9
Mopar MPI rough running issue

Hi All!

I have the Mopar MPI injection on my CJ and it has started to run poorly, it started out somewhat intermittently but now happens consistently. It starts right up, runs smooth for a few minutes and then goes to crap. It runs really rough, more than just one fouled plug type of chugging, its more like a rumble strip on the side of the highway type shuddering... its "seems" to come out of it with RPM, as when I am going down the road and I get on it is seems to go away, or I cannot feel it any more at least. If I leave in gear (standard) when going down even a slight grade it will back fire. It smells of unburned fuel badly. I have checked fuel PSI, its around 40, I have changed plugs, cap, rotor, wires, and coil, with no improvement. Might it be a crank sensor? I don't think its mechanical (timing chain) because it seems to run ok for brief amounts of time esp when I first start it.

For a little while shutting it off and restarting it seemed to help.. (clue?)


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post #2 of 7 Old 09-03-2013, 08:58 AM
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1984 CJ7 
Join Date: Sep 2007
Location: Sarasota, Florida
Posts: 109
I have the same set up. It could very well be the the crank sensor. You can get those locally at the parts store for cheaper. I had mine go bad. It is not uncommon, it the first thing I would replace.

Good luck.

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post #3 of 7 Old 09-03-2013, 10:46 AM
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1985 CJ7 
Join Date: Jun 2008
Location: Chicago area
Posts: 3,549
Take it down to Auto Zone and borrow a scanner and find out what the real problem is then address it. Otherwise you will be throwing parts at it.
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post #4 of 7 Old 09-03-2013, 07:59 PM
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1982 CJ7 
Join Date: May 2007
Location: Chino Hills, CA
Posts: 136
Any codes come up on check engine light? read this near the end
If all else fails, ask Hesco
tombstne is offline  
post #5 of 7 Old 09-03-2013, 08:23 PM
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2003 TJ Wrangler 
Join Date: May 2007
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still sounds like a coil break down, just went through it myself. aftermarket coils are junk (surprise ! ). there's a good thread on the yj board from the past about coil problems with the 4.0. goggle search it.
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post #6 of 7 Old 09-10-2013, 07:21 AM Thread Starter
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1982 CJ7 
Join Date: Jul 2013
Location: Vershire
Posts: 9
problem solved

Thanks for all the great advice, I though coil too, but when I found the #1 injector "running" all the time, I knew something else was up. The long and short of it was the wiring harness to the ECM was just a bit too close the the exhaust at the rear of the engine. When it warmed up the ground wire to the #1 injector would short to the exhaust and make the injector run all the time. As I learned the injectors have power anytime the key is on and are grounded at the right time to open. when mine grounded it just flowed fuel constantly. Once I got the harness out where I could fix it, Bam! it ran great again! (Yea!)
thanks again for the help folks!
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post #7 of 7 Old 09-10-2013, 10:19 AM
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1986 CJ7 
Join Date: Nov 2009
Location: California
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Thanks for coming back and letting us know what was wrong and how you fixed it. This will help others who find this thread later.
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