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Unread 03-21-2010, 06:46 AM   #1
SXMjeep
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1996 FSJ Cherokee 
 
Join Date: Jun 2009
Location: Sint Maarten, NA
Posts: 4
4.0 running erratically and quits

Hi there, my Jeep has been in the Caribbean a little too long maybe. So it quits after about about 5 minutes of running. Sometimes it idles at 1300 rpm, sometimes it has a very bad rough running/missing problem at idle. Shutting the engine off and restarting usually fixes this temporarily.

I have replaced, and had replaced by mechanic (their diagnosis):

(96,000 miles on motor)

Fuel pump, filters, relay
Crank position sensor (twice)
Throttle position sensor
distributor cap
both oxygen sensors

The head gasket had to be replaced and head was checked for warping after overheating some time ago. One mechanic said the PCM may have overheated.

Time for a new computer maybe or??? don't want to buy any more parts I don't need.

Thank you all.....regards.

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Unread 03-21-2010, 07:02 AM   #2
xjfever
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1995 XJ Cherokee 
 
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Location: north Ga.
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I would test the coil they are subject to thermal failure. Also how many miles on the plugs, wires, cap, and rotor? Cleaning the throttle body and IAC wouldn't be a bad idea either. The PCM can go out but it is very unusual.
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  2. Sold'99 WJ limited, 4.7L, 3" IRO lift. Bilstein shocks, JK rubicon wheels, 255/70/17's, carolina driveshaft, IRO adjustable control arms, IRO adjustable A-arm
  3. Sold '00 TJ, 4" lift, rusty's adjustable control arms, skyjacker shocks, rock krawler adj. trac-bar,rugged ridge SYE and RE driveshaft, soft 8's, 35" mud king xt's,XJ HP D30 w/aussie locker, 4:88 yukon gears, hella 500's, rock crusher diff covers
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Unread 03-21-2010, 08:20 AM   #3
SXMjeep
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1996 FSJ Cherokee 
 
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Location: Sint Maarten, NA
Posts: 4
Thanks! I tested the coil in accordance with the Jeep manual, and it checked out. Can they fail intermittently though? Plugs cap and rotor are all recently replaced although they put some different center electrode high performance plugs in. The plug wires, unknown. I will try this next. The throttle body was cleaned. Thank you again for your reply...

regards
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Unread 03-21-2010, 08:39 AM   #4
xjfever
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1995 XJ Cherokee 
 
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The coil can fail intermittenly. Best to test it when it is hot and acting up. Copper core champion plugs seem to work best in the 4.0L. The camshaft position sensor under the distributor cap is another item that can give similar problems.
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  1. '95 XJ country edition, 4" coils/3/4" spacers, HD leafs with extra main added in, Ironman adjustable control arms, rough country shackles, aussie locker, JK rubicon shocks, 35" mudder's, soft 8's, cobra cb
  2. Sold'99 WJ limited, 4.7L, 3" IRO lift. Bilstein shocks, JK rubicon wheels, 255/70/17's, carolina driveshaft, IRO adjustable control arms, IRO adjustable A-arm
  3. Sold '00 TJ, 4" lift, rusty's adjustable control arms, skyjacker shocks, rock krawler adj. trac-bar,rugged ridge SYE and RE driveshaft, soft 8's, 35" mud king xt's,XJ HP D30 w/aussie locker, 4:88 yukon gears, hella 500's, rock crusher diff covers
4. 04 Dodge ram 1500 quadcab, yes, it has a hemi.
5. '08 BMW X3, Mods in progress.
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Unread 03-21-2010, 08:48 AM   #5
cruiser54
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Plug wires should be a priority. They're a maintenance item anyway.
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Unread 03-21-2010, 08:54 AM   #6
tjwalker
It's the crank sensor!
 
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Is there a check engine light on or have you seen one? If so, you must pull the stored codes for guidance.
In the absence of codes, if this were my vehicle, here are some things to consider:

1. You mention the throttle body was cleaned. It is very important that the "idle air control" is thoroughly cleaned and also clean throughly where the IAC seats in the throttle body. Very important to idle quality. If you haven't done this, doing so is a must.

2. Test your camshaft position sensor. Located inside the distributor. It is responsible for fuel injector timing as well as other things. Gotta rule it in or out in this troubleshooting process. Will need a meter and a manual and as you said you tested your coil, sounds like you have both of these.

3. Although the spark plugs are not likely the cause of your intermittent problems, I'd get some plain old copper champions installed. Replace plug wires for sure.

4. Test coil when symptomatic as already mentioned.

5. I can't recall for sure but I think that on a 96, the fuel pressure regulator is part of the fuel pump so am assuming that was replaced. However, it never hurts to actually verify fuel pressure at the schrader valve on the fuel rail. Can't assume anything and proper fuel pressure is a data point that must be taken.

Good luck and let us know what you find!
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Unread 03-22-2010, 08:29 AM   #7
SXMjeep
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Thank you! I am working on it, I am suspecting the Cam position sensor and will test it first. When the engine runs rough or quits sometimes it acts exactly as if "something" is out of time (violent miss, dieseling, smoke), the injector timing would explain that, ....when it's running, the motor idles and accelerates very smoothly........I will let you know~ your help is truly appreciated.
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Unread 05-04-2010, 06:29 PM   #8
SXMjeep
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1996 FSJ Cherokee 
 
Join Date: Jun 2009
Location: Sint Maarten, NA
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Ok guys ....well here is what the problem was. I see others have solved this the same way...it was the screws in the cover of the PCM ...cut them in half and they stop touching the circuit board and killing the motor. The 4.0 is happy again. Incidentally, the PCM has a "rebuilt" sticker from Mopar on it, the first one probably had the same problem. Thanks to all for the help!!
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