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Unread 08-06-2012, 02:49 PM   #1
s_staples35
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1995 ZJ 
 
Join Date: May 2012
Location: Goffstown, New Hampshire
Posts: 5
1995 Grand Cherokee 4.0 losing spark when hot.

My 95 Grand Cherokee is losing spark when hot..

The engine starts and runs great when cool. I can drive it for about 25-30 miles before it cuts out. I usually have to wait about 45 minutes to an hour before it will start again. Also noticed it is much better on the highway.

I think it is the PCM is telling ADS relay to kill power to the coil and injectors.

While it is "shutdown mode" with the key in the on position. I have recently noticed a buzzing sound in the transmission (possibly governor solenoid) Not sure if this is telling the PCM to kill it or not, since this doesn't have a separate Trans control module.

ADS relay,TPS, and Fuel Pump, are all fine.

Prior to discovering this I have change the crank sensor (twice), cam sensor, coil (twice), distributor cap, rotor, all plugs and wires.

Today I noticed after it dies if I unplug the crank sensor and plug it back in the ADS relay clicks, and will sometimes start right back up. I have just ordered a new crank sensor from the dealer this time. NO MORE aftermarket electrical parts for me.

I've got my fingers crossed. However-If anyone has any advice it would be greatly appreciated.

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Unread 08-06-2012, 05:01 PM   #2
johnt671
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1998 ZJ 
 
Join Date: Nov 2011
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Posts: 98
I'm not a real experienced Jeeper, but on one of my cars I've had for 15 years your problem is a sign of a bad ignition module.
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Unread 08-06-2012, 07:27 PM   #3
JasonStebbins
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1997 ZJ 
 
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Crank Position Sensor. Or the ignition coil or bad connection at the distributor/cap. Wiggle the three PCM connectors while running, any change in idle is bad.
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Unread 08-06-2012, 09:42 PM   #4
Uniblurb
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1996 ZJ 
 
Join Date: Jan 2012
Location: Central, Ohio
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My guess would be crank sensor and I had 2 new aftermarket ones which never did work right. A Mopar one fixed my problems.

Also make sure your grounds are good/clean, especially your engine grounds. The cranks sensor is grounded through the PCM and the PCM is grounded to the block. I lost my PCM due mainly to bad engine grounds and bad grounds cause havoc with sensors.

BTW. You may want to change your profile to where it just reads "1995 ZJ". XJ = Cherokee, ZJ = Grand Cherokee.

Good luck.
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Unread 08-07-2012, 05:20 PM   #5
s_staples35
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1995 ZJ 
 
Join Date: May 2012
Location: Goffstown, New Hampshire
Posts: 5
Thanks All,
I have narrowed it down to a problem before the coil. The 95 only has one connection at the PCM and I have wiggled it and every other connection on the harness. No changes weather running or not.
Also, I have gone through the entire thing and cleaned up all connections and grounds without any change.
Hoping the new Mopar CPS is the key.. just picked it up today.

Thanks Uniblurb, didn't realize my Jeep type was wrong on my profile.
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Unread 08-07-2012, 10:14 PM   #6
Uniblurb
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No problem s_staples and welcome to the forum!

Hopefully the Mopar crank sensor will fix your problems.
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Unread 08-09-2012, 04:20 PM   #7
s_staples35
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1995 ZJ 
 
Join Date: May 2012
Location: Goffstown, New Hampshire
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Thanks,
Finally after a few years of dealing with this problem I believe it is fixed!
I am convinced that was exactly the problem. I put the new factory sensor in and haven't had any issues since.
Apparently Jeep PCM's don't like aftermarket sensors. I had put two new Borg Warner crank sensors in prior to this, and neither of them ever worked properly, and they were not much cheaper.
All Mopar electrical parts from here on for this Jeep and my new '99 Grand Cherokee.
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Unread 08-10-2012, 12:43 AM   #8
Uniblurb
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Good deal and glad you're back on the road!

Those faulty aftermarket sensors are something most of us have dealt with and we have also learned our lesson to go with Mopar.
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crank position sensor , intermittent , no spark , stalling
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