Question about 1994 Jeep Grand Cherokee

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1994 Grand Cherokee, 5.2 V8 shuts off when hot. Cool for an hour or 2, starts up ok for a half hour or so, then dies again. No trouble codes except 12 and 55; I pulled fuses to check them, hence the code 12. When it dies, check engine light dies with it- turn key on, no check engine light. Car won't start untill the check engine light works again; after cooling off for 1-3 hours. Also, tachometer goes to zero immediately, as though it's losing the TD signal- coasting, engine still turning, but no tachometer. Swapped out coils, no help. Checked pcm connections, seem ok.

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  • philsbmw Oct 07, 2010

    @Kevin- That's the current theory- I'll pick up another PCM tomorrow and give it a try. I'm driving now on the original pcm I repaired, which mysteriously seems fine now...but I don't trust it, it's quit since the repair, just not recently!
    Another post summed it up very well- when you've had a computer problem with your jeep, confidence is the key word!
    I'll post results as they develop-

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  • Jeep Master
  • 1,453 Answers

Your engine computer is bad. It's a good thing that you mentioned about the check engine light dying also, as this is a classic sign of a bad ecm. I have repaired more than one of these Jeep computers, replacing the three power capacitors located inside the computer, and they have worked for years afterwards. If you don't have the skills or knowledge to repair the ecm, get yourself a rebuilt ecm unit and swap it out.

Posted on Sep 28, 2010

  • 3 more comments 
  • philsbmw Sep 30, 2010

    Replaced the 3 caps, but it didn't solve my problem- symtoms are unchanged. I guess I'm looking for a salvage pcm- let me know if there's anything else I should be looking at. I'll post my results step by step til it runs.

  • philsbmw Oct 01, 2010

    Swapped out the pcm. Now the check engine light seems to behave normally, and the car starts up every time- but dies after a few seconds. No fault codes but 12 and 55. I have jumped both the fuel pump and asd relays, it still stalls after a few seconds.
    Any opinions? I'm stumped!

  • Kevin Daniels Oct 05, 2010

    Make sure the pcm you got didn't come from a vehicle with factory security(unless your vehicle also has factory security). That might cause the few seconds after start-up shutdown you're describing.

  • philsbmw Oct 07, 2010

    @Kevin- the security compatability problem is the current theory. The salvage yard has come up with another pcm, I'll try that and see what I get. For now, I'm driving it locally on the original pcm that I replaced the caps in, but I have no confidence in it; this box has stopped me since the repair, and could do so again anytime.
    I'll post results as they come......I can find no reference to a part number or any way to identify pcm's with/without security, so I think it's a **** shoot at this point. Nice work, Dodge. :(

  • philsbmw Oct 07, 2010

    For the record, my original pcm is a 56028112, and the car does not have the factory security system. The replacement pcm, which starts and runs for 2-3 seconds every time, then shuts down, is a 56029302. This is from a salvage yard, it's unknown if the donor car had the security option.
    If it'll help anyone with the same problem, I got the pcm repair procedure from http://www.jeepforum.com/forum/f13/fixin...
    which also has great pictures of the process, as well as the part numbers of the replacement capacitors required- many thanks to the poster, gomes512.
    Off to pick up another pcm, I'll let you know how it turns out.

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1994 Grand Cherokee, 5.2 V8 shuts off when hot. Cool for an hour or 2, starts up after a half hour or so, then dies again. No trouble codes except 12 and 55; I pulled fuses to check them, hence the code...


NOTE: With the jeep cherokees. the Check Engine light if continuously driven with it on for more than 25 minutes whilst still traveling will engage the "PCM self protect" usually around the 27minute mark,and shut down the vehicle, and yes it takes 90 minutes to reset,

you might find that you will arrive ok, at your destination with this issue... pull up, and then it wont start again a few minutes later, this is the PCM Shutdown protection.....when the check engine light is on means the PCM is reset,found the error and why you can only run the car with the check engine light for about half an hour.

"You can however drive and turn the car off and coast in neutral and turn on the vehicle again to buy yourself more time with the "Check Engine time limit shutoff"

happened to me in mine, the error codes never showed up for the crankshaft position sensor
either...

i replaced the crankshaft position sensor under the transmission case, and it got rid of the issue this crank sensor is a common cause of the cherokees , it could no longer read the speed of the crankteeth. and can't get a reading the car is still running hence the shutdown, also you will find it also controls the PCM to engage your second fan on the radiator because it cant tell the vehicle is still running, and causes the PCM to get confused and wont let the rest of the engine function properly ie: coolant sensors, and Thermostat sensors, and you will find it overheats and needs to cool some times...which is why the PCM shutsdown the car.....try the crankshaft position sensor replacement under the transmission it's usually the cause of this on all cherokees "makes no difference if its a V8 or not by the way, same thing happens on 4.0 straight six engines also" .

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sounds like a bad pump, filter or both. Do some testing before replacing though, a bad crankshaft sensor can do pretty much the same thing! Parts are not cheap...testing is very important!!!

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Check the fuel pump, make sure it is putting out proper pressure if not then change the fuel pump

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My car starts and then dies


sounds like a security issue they installed a factory security system which will prevent the vehicle from running unless its reset go to passenger door lock turn key twice it worked for me after chasing other problems for a few hours

Dec 03, 2008 | 1995 Jeep Grand Cherokee

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