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Mark, 22 Year Factory trained technician
Category: Jeep
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Experience:  Jeep factory training........25 years in the industry.
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I have a 96 Jeep Grand Cherokee with a crank but no start

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I have a '96 Jeep Grand Cherokee with a crank but no start situation. Here are the sordid details: Discovered the ground to the fuel pump and the power wire for the fuel guage shorted together- resulting in a dead fuel level guage, as well as a dead volt guage. Check engine light does not come on when turning on ignition. All fuses and relays check out okay. Is there another computer on this vehicle besides the under hood PCM? By the way, I've already replaced that as well (the PCM), and the vehicle still shows 214370 for mileage (same as old PCM) leading me to believe there is another computer on this vehicle. Help me please!!!
Submitted: 6 years ago.
Category: Jeep
Expert:  Mark replied 6 years ago.

Good morningCustomer my name is Mark

 

Seems like you have your hands full on this one. Do you have access to a scan tool? I think that would be most helpful in this case.

Customer: replied 6 years ago.
what other information would you like? As for the scan tool, no I don't have access to one. Is it possible to try to jump the two terminals like on GM's?
Expert:  Mark replied 6 years ago.

If your check engine light doesn't work then it won't flash any fault codes for you. You are going to have to test all the powers and grounds going to the computer. When you replaced the PCM, was this new or used.

 

One other thought, a shorted 5 volt sensor can cause the PCM to shut down. These include the tps, map and crank sensors.......and a few others. Try disconnecting these one at a time and see if your check engine light comes back. You can also test for 5 volts at these sensors and disconnect them one by one until the 5 volts returns. Hope that makes sense to you.

Customer: replied 6 years ago.
Two quick follow up inquiries- where would the crank sensor be? I looked at tthe front of the engine but couldn't find anything wire related that looked like it might be a crank sensor. Is it possible it's in the flexplate area between the trans and the engine? Also, I know there's another computer somewhere in the system, besides the underhood PCM. The reason I have cometo this conclusion is the fact that when installing the replacement, my odometer showed the same mileage as when I had the original PCM in it. By the way, it's a used PCM from a confirmed running crash vehicle. I heard the vehicle run. I'll check the sensors, but I feel deep down inside it's that secondary computer. I know if they get a dead short for even a split second, it can wipe the memory rendering them non-functional. I just need to know where that one is located.
Expert:  Mark replied 6 years ago.
The crank sensor is located on the bellhousing on the drivers side. The connector should be accessible at the rear of the intake manifold. The second computer you are refering to is the body control computer. It's under the dash on the left side but it is a BODY computer not an engine computer.
Customer: replied 6 years ago.
isn't that the computer that has the memory for the odometer, guages, etc? I have gone from one PCM to the other, and gotten the same mileage on the odometer, which leads me to believe that the second computer is the culprit. I have been told in situations such as mine, when the computer experiences a dead short, it can erase the PROM, rendering it nonfunctional. I looked under the left side of the dash and noticed the computer for the anti-lock brakes, but didn't notice any other computers. Is the body control module mounted high under the dash? You had also mentioned the crank sensor previously. The reason I haven't focused on that is the fact that multiple things are dead- fuel pump, fuel guage, volt guage, no spark, check engine light. You also mentioned that one of the sensors could be shorted. Would that in fact affect all of these items and NOT damage the computer? Sorry for being so longwinded, but this thing is driving me up the wall. I really don't have the money to take this to a professional mechanic. Or a non professional for that matter. Thanks again for your help.
Expert:  Mark replied 6 years ago.

Yes the BCM stores the mileage that is why it stays the same when you change the PCM.

 

Did you try disconnecting the crank sensor as I suggested and checking for the 5 volt supply voltage.

 

I understand you seem to be fixated on this "second" computer but unless the communication bus has gone down, it will have zero effect on your no spark, no check engine light.

 

A shorted sensor causes the computer to shut itself down so it doesn't get damaged......kinda a fail safe mode. Once the short is removed the PCM will be fine.

 

You stated you didn't have a scan tool but do you have a volt meter?

 

 

This is a PAY SITE so if I have answered your question to your satisfaction a simple ACCEPT would go along way. Feedback and Bonuses are also welcome.

Mark, 22 Year Factory trained technician
Category: Jeep
Satisfied Customers: 11273
Experience: Jeep factory training........25 years in the industry.
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