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Unread 06-25-2013, 05:17 PM   #1
SpringhillJim1
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1996 WJ 
 
Join Date: Jun 2013
Location: Spring Hill, Florida
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Jeep Cutting out about 50 MPH

My 96 5.2 V8 4x4 Grand Cherokee runs fine then after it heats up and I am running about 50 mph It cuts out like the key was turned off the comes right back on. If I slow down to 45 it doesn't do it. It's not overheating( just replaced the radiator, water pump and hoses).
Does anyone have any ideas what could be causing this?

Thanks,
Spring hill Jim

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Unread 06-25-2013, 05:36 PM   #2
Will9119
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1996 ZJ 
 
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Location: Kingsport, TN
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Could be the crank sensor. I had mine replaced with similar symptoms except it would cut out at many different speeds. Could also be throttle position sensor.
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Unread 06-25-2013, 06:00 PM   #3
a70eliminator
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Mine did exactly what you describe, especially pulling my boat, sometimes I had to come to almost a complete stop and then proceed gradually, it got so bad I had to do something, it ended being the fuel filter, the guy asked me when it was last changed "never" I would have never quessed the engine was starving for gas.
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Unread 06-25-2013, 06:15 PM   #4
AaronButler
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1996 ZJ 
 
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I dont think it would be the TPS, but the Crank position sensor could be at fault. Or your computer. Does it start back up after it dies?
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Unread 06-26-2013, 08:12 AM   #5
SpringhillJim1
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Yes it starts itself right back up but makes a heck of a jerk. I have changed the fuel filter because it was about 5 years old, but that didn't help
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Unread 06-26-2013, 08:28 AM   #6
JS97ZJ
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Turn the key on and off 3x and leave it in the run position with the engine off. Codes will show up on the dash. Post what you get.
It sound like the CPS though.
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Unread 06-26-2013, 08:40 AM   #7
SpringhillJim1
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Location: Spring Hill, Florida
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I get a check engine and check gauges on the dash. I think I will run over to Autozone and get them to check the computer codes. Will the CPS show up if it is bad?
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Unread 06-26-2013, 08:46 AM   #8
JS97ZJ
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Not all the time. Getting the P codes is a more exact way of getting to the problem but you can also get them doing the key trick.
You always start troubleshooting with getting the codes.
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Unread 06-26-2013, 08:54 AM   #9
dellis
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Quote:
Originally Posted by SpringhillJim1 View Post
Will the CPS show up if it is bad?
Not necessarily.

But, I can't think (logically) of a reason why this would be the Crankshaft Position Sensor. Although a bad CKPS causes engine cut-offs, it makes little sense that it fails because the frequency hits a certain mark.

More likely, I would think, would be a fuel related problem - perhaps your pump. But, I'm curious first about the codes you get.
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Unread 06-26-2013, 08:57 AM   #10
SpringhillJim1
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Sorry I wasn't looking at the odometer. The codes are 12 21 55

Thanks
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Unread 06-26-2013, 09:25 AM   #11
dellis
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12 - Battery Power to PCM disconnected
55 - End of codes

21 could be one of several codes (it can be narrowed down with an ODBII scan tool), but all relate to the O2 sensors. If it were me, I would (a) put an ODBII scan tool on it to get the exact codes, and (b) change my upstream O2 sensor.
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Unread 06-26-2013, 10:39 AM   #12
SpringhillJim1
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The O2 sensor wouldn't make it cut out and jerk like that would it?
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Unread 06-26-2013, 11:03 AM   #13
dellis
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Quote:
Originally Posted by SpringhillJim1 View Post
The O2 sensor wouldn't make it cut out and jerk like that would it?
Perhaps. If an O2 sensor is not correctly reading the exhaust, then it could cause a too rich or too lean condition as the PCM compensates. For me, the first thing I would do is get the exact code from an ODBII scanner to help with diagnosis.

I'll admit that I am perplexed by the deep mysteries that are programed into the PCM's operation. But, our Jeep PCMs are not very robust when it comes to faulty sensor readings ... if the readings are off, the PCM does the unfathomable thing of allowing our engines to sputter, jerk, and die. If you read these forums enough, you will find that there are perhaps a dozen different sensor errors that can cause a Jeep's PCM to kill the engine (it has no "limp" mode). That, in my opinion, is very poor engineering.
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Unread 06-27-2013, 07:29 PM   #14
dusterdude
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My cps had a very weak magnet
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