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Daniel Wilson
Daniel Wilson,
Category: Jeep
Satisfied Customers: 4291
Experience:  Owner at DJ Wilson
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Grand cherokee: Chris, Working on a '97 Grand Cherokee

Customer Question

Hi Chris,
Working on a '97 Grand Cherokee 4WD, 5.2L that was towed in. Engine stalled while driving and would not restart. We were able to get it started after it cooled down by holding accel to the floor and cranking it. Once it starts to warm up the idle becomes erratic to the point it nearly stalls starts pinging badly. Left on its own it will eventually stall and not restart until cooled down again.
I have no communication with PCM and checked wiring from DLC to PCM, all ok. Also power and grounds ok at both DLC & the PCM.
IAC, seems to work normally.
IAT and CTS values test ok, grounds ok.
Disconnected heated o2 sensor.
Cut bus lines at PCM to see if anything else may be taking PCM down, no change.
Came in with reman PCM, have subsequently tried 2 more A1 Cardone reman PCM's.
We are primarily a Mercedes shop but am trying to help an MB owner that owns this as a second car.
Submitted: 5 months ago.
Category: Jeep
Customer: replied 5 months ago.
Forgot to mention fuel pressure 49 psi at all times.
Expert:  mike switzer replied 5 months ago.

out of curiosity when it stalls out what are your fuel trims. sounds like something is cutting fuel off.

Customer: replied 5 months ago.
How can I read fuel trims?
Customer: replied 5 months ago.
anyone there?
Expert:  mike switzer replied 5 months ago.

im sorry my system crashed and has just gotten back up. you will need a scanner to look at the data and look at the long and short term fuel trims.

Customer: replied 5 months ago.
Not to sound sarcastic but did you fully read my description of the problem? The whole reason I am having trouble diagnosing this is because there is no communication with the PCM.
Expert:  Tim Mohr replied 5 months ago.

Hi, my name is***** can help you with this, does the check engine light come on, for about 2 seconds when the key is first turned on?

Customer: replied 5 months ago.
Hey Tim, I don't know what happened to my reply to you, I just refreshed this and I see it didn't come up. Anyway, the check engine light was not on until we started disconnecting things so the pcm does see those missing inputs (iac, cts, o2s, etc) but for whatever reason I cannot communicate with the pcm via either my snap-on or launch scanners.
Expert:  Tim Mohr replied 5 months ago.

Yes, but does the light come on when you turn the key on, for a bulb check?

Customer: replied 5 months ago.
Comes on and stays on with key on.
Expert:  Tim Mohr replied 5 months ago.

If the light comes on, then you have all powers and grounds to the PCM, and you have a bad PCM, if all the wires have been ohmed out, then it can only be a bad PCM, A-1 cordones have more problems than there woth, have all the PCM been A-1 cordones?

Customer: replied 5 months ago.
When it came in it had a reman pcm from auto computer exchange (I think that was the company).
Expert:  Tim Mohr replied 5 months ago.

I would try a dealer PCM, we have nothing but problems with aftermarket PCM's on these,Tim

Customer: replied 5 months ago.
Well, couldn't get the owner to pony up for oem so I'm kinda stuck with the aftermarket but they are sending me yet another so I guess we'll see tomorrow when it shows up!!!
Customer: replied 5 months ago.
Third PCM and still no communication. Do you know if pin #7 (SCI transmit) on the data link connector should go to ground? I have 1.5 ohms to ground on that terminal with the PCM unplugged.
Customer: replied 5 months ago.
Expert:  bill replied 5 months ago.

hi i'm bill let me see if I can help one of the moderators messaged me to try and assist you, I have been with jeep since 1992 and still work at a Chrysler dealer

Expert:  bill replied 5 months ago.

can you send me the vin so I can pull some wiring diagrams, also we have had many issues with crank position sensors shorting and crashing the pcm if you unplug the crank sensor can you communicate with the pcm, the crank sensor connector is behind or VERY near the distributor you will find 2 connectors there 1 will go to the distributor pick up (cam sensor) and the other will go towards the right that's the crank sensor

Expert:  Daniel Wilson replied 5 months ago.

Hi Martin, My name is***** the crank sensor tests okay and the distributor and coil is okay verify the timing is still in specs and the engine has not jumped time. Click here for some schematics as well to assist in testing the circuits.

Diagrams/ Troubleshooting

Customer: replied 5 months ago.
Hello Bill and Dan and thank you for your replies. As I mentioned to the moderator, I was gone the first 2 days of this week and am playing catch-up. I will check the things you both mentioned as soon as I can and report back. Will likely be tomorrow at this point, though.
Thanks again,
Customer: replied 5 months ago.
Sorry, forgot to add the VIN, it's:1J4GZ78Y9VC565998
Expert:  bill replied 5 months ago.

it's rare to see a old school v8 to jump time, you MAY be able to pull codes with the old key cycle method used on pre 96 vehicles do you have all data r the like? if so there is a test for the crank sensor if not let me know and I will dig one up

Customer: replied 5 months ago.
Hey guys, well we pretty much figured out why it runs so bad - when we pulled it in the shop today we discovered there wasnt a drop of coolant in the radiator (it never once showed it was running hot on the gauge so we didnt even suspect that) and when we added water it was literally running out the tailpipe and thru several rust holes by the cat pipe and also coming out the front of the head. I think its a death knoll for this thing as I seriously doubt its even worth fixing.
Expert:  Daniel Wilson replied 5 months ago.

Thanks for the update Martin, Sorry to hear the bad news. Might be less money to do a used engine swap if it is decided to fix it. Hope you have a great afternoon.

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