Infamous stalling problem identified, temporary cure 1997 grand Cherokee - Page 2 - JeepForum.com
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post #16 of 888 Old 10-09-2010, 10:21 AM
JensGCherokee
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Quote:
Originally Posted by ZeeJay1997 View Post
That's a new one on me. Never heard of oil gauge associated with stumble. Not sure how it works on a 95, but on a 97, the oil pressure sending unit feeds the PCM, PCM feeds the instrument cluster on the CCD bus. In the mean while, the BCM monitors the PCM output and turns on the low oil pressure light if the pressure goes too low.



Does the tach seem to follow what the engine is doing, or does it go rogue?
It goes with what the motor is doing.. Same with the oil gauge. I checked the oil level which is good, and also ran another oil pressure gauge (temp) & it didnt agree with the one on the cluster. The Tach on the other hand, reads exactly (+/- maybe a few RPM) of a temp gauge.


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post #17 of 888 Old 10-09-2010, 11:01 AM
ZeeJay1997
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Quote:
Originally Posted by JensGCherokee View Post
It goes with what the motor is doing.. Same with the oil gauge. I checked the oil level which is good, and also ran another oil pressure gauge (temp) & it didnt agree with the one on the cluster. The Tach on the other hand, reads exactly (+/- maybe a few RPM) of a temp gauge.
This could be indicative of a bad ground or shorting across circuits within the ECM. Have you tried tapping the ECM and wiggling connector?


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post #18 of 888 Old 10-09-2010, 11:22 AM
Canyon411
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.... It sounds like this "stumble/surge" issue is quite common to grand cherokee's. I have been dealing with the same issue on my 95zj and I was tempted to replace alot of the usual suspects such as the idle air control or throttle position sensor. I even considered coil, plug wires, etc. The thing that bugged me the most about the stumble/surge issue was that it was never consistant. I would go three months and never have an issue and then it would start again.

Generally when a sensor goes bad, it creates a consistant problem, not an intermidant one. That is why I have held off replacing the above components and kept looking for a possible cause that would support the intermidant nature of the problem, and the underhood environment where the pcm lives is constantly bombarded with temperature changes, moisture fluctuations, and viberation. It all kinda makes sense so the next opportunity I have, I will be pulling the coolant recovery tank and unplugging the wiring harness connectors to the pcm for inspection of corrosion and loose pins/black marks from shorting or loose connection. A good cleaning with contact cleaner and some fresh dielectric grease hopefully will excersize the stumble deamons from my zj
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post #19 of 888 Old 10-09-2010, 12:19 PM
JensGCherokee
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Originally Posted by ZeeJay1997 View Post
This could be indicative of a bad ground or shorting across circuits within the ECM. Have you tried tapping the ECM and wiggling connector?
I have not tried that yet. I will be doing that tonight. Wiggiling it at first.. I am dropping my daughter off at my fathers for the night, so the short 15 min drive there hopefully will turn over a stone, if not.. Un-plug it & clean everything, refresh the dielectric greese, & see how it runs tomorrow when I pick her up.

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post #20 of 888 Old 10-09-2010, 12:42 PM
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Quote:
Originally Posted by JensGCherokee View Post
I have not tried that yet. I will be doing that tonight. Wiggiling it at first.. I am dropping my daughter off at my fathers for the night, so the short 15 min drive there hopefully will turn over a stone, if not.. Un-plug it & clean everything, refresh the dielectric greese, & see how it runs tomorrow when I pick her up.
If it runs good for 3 warm up cool-down cycles, then starts acting up again, start hunting an ECM.


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post #21 of 888 Old 10-09-2010, 11:20 PM
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One of my customers with a '96 ZJ 4.0L had this stalling problem. We initially installed the zip ties, as per ZeeJay1997's photo, but the problem returned after about a month and a half. We designed and installed a metal bracket to replace the zip ties, and so far (4 mos, 8K miles) the stalling problem has not returned. If anyone is interested, I'll post photos (which I'll take the next time this customer's ZJ is in my shop).
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post #22 of 888 Old 10-10-2010, 07:26 AM
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post the photos, wouldnt hurt to get another idea!!!
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post #23 of 888 Old 10-10-2010, 01:51 PM
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Quote:
Originally Posted by tireworlddave View Post
One of my customers with a '96 ZJ 4.0L had this stalling problem. We initially installed the zip ties, as per ZeeJay1997's photo, but the problem returned after about a month and a half. We designed and installed a metal bracket to replace the zip ties, and so far (4 mos, 8K miles) the stalling problem has not returned. If anyone is interested, I'll post photos (which I'll take the next time this customer's ZJ is in my shop).
Yes, please take photos when you can, I'm starting to have a stalling issue (about once/week) and I may do that, before I start spending $$ replacing other items.

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post #24 of 888 Old 10-13-2010, 09:58 AM
JensGCherokee
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ZeeJay,

Nothing changed. Wiggled it, got maybe 5 mins from my house & it started up like usual.. Got home, unplugged it, looked the connectors over and seen no blackening or corrosion but still cleaned them, plugged it back in & left it sit over night. Took it to pick my daugter up, and again started right back up. Now, as i mentioned (or at least thought I did) this issue did not happen before the Crank sensor was replaced. Everything worked fine before it died. Could it be possible that i got a faulty crank sensor? I didnt know they can intermittenly cut off for a second.. I thought if they go, they go..

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post #25 of 888 Old 10-18-2010, 09:46 AM
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Well, I think my issue is solved... I was checking the fluids (as I always do) & I had no trans fluid at all!! Which I think is weird since I did check it prior to it going down. Since last year, I have only put 1,000 on it! No spots under the Jeep where it sits, but noticed the trans pan gasket is shot, and it's leaking around the bell housing. Just gives me an excuse to put a better trans in.

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post #26 of 888 Old 10-18-2010, 08:41 PM
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Loose PCM plugs seem to be a common problem. I like the zip-tie method for holding the plugs in place. I used a couple hose clamps connected together but mine had a bad plug on the outside. I may go get some of those industrial sized zip-ties and replace the hose clamps. Then again, I have been running almost two years with the hose clamps without a return of the problem so maybe I'll just leave it alone....don't want to jinx it.

I also have replaced the crank angle sensor (not the problem), and the cam angle sensor. The cam angle sensor (inside distributor) was definitely bad and caused random stalling and misfiring. This occurred prior to the problem with the PCM connector.

The main symptom of the loose connector was the idle speed would drop to below 700rpm whenever I slowed down or stopped. The engine would spit and sputter and idle speed would not come back up, after a few seconds it would stall.

See post #11

http://www.jeepforum.com/forum/f13/9...lp-plz-858230/
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post #27 of 888 Old 01-22-2011, 09:36 PM
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I'm going to try the hose clamp fix myself. I have been struggling with stalling for about a month now. As a matter of fact, my PCM looks just like the one with the hose clamp. Connector C1 (black) missing the locking tab. I have tried the magic screw repair and zip ties. Screw worked for a day and zip ties worked for about a week and then I had a hiccup followed two days later by a full blown stall. Now it's stalling about 4 to 6 times in a one way trip to work (11 miles).
I was able to procure a clamp tonight and got it installed. When I go home we'll see. I was throwing a P0351 code with a code 43. This is an aggravating fault to be sure. I am an aircraft electrician by trade so and thanks to the volumes of people who have had this problem I have been able to do some really good fault isolation.
It exists either in the C1 connector for me or the PCM. Initially I changed the TPS and then found found C1 ready to fall off the PCM (Thus the zip ties).
Later I found that even though zip tied wiggling the harness could duplicate the fault. So another zip tie around the harness to pull tension on the connector. The fault returned. I also took a rubber mallet to the computer while the engine is running and duplicated the fault as well.
At this point I'll try the hose clamp and see how that works out. Either I don't have a good connection on C1 or the male pin 7 in the computer is a problem. Since I have an obvious defect in the locking tab on the C1 connector I'm swaying towards that.
I want to talk a little system knowledge here courtesy of a guy who posted on CNet.
1. P0351 is a coil code. However:
a. The coil receives a signal from the PCM connector C1 Pin 7 to "fire".
b. There are only two wires at the coil, signal wire from the PCM pin 7 and a ground wire.
c. In order for the PCM to throw code P0351 the PCM had to fail to send the proper fire signal. Of course this assumes that you have a known good coil, clean ground and no breaks in your wiring.

2. A multimeter checks continuity not integrity. The average 18 gauge wire has 22 individual copper conductors(wires) inside the insulation. You can have 21 broken strands and still read full continuity through that single strand of wire. But that single strand of wire will not be able to handle the signal being sent to the coil (load). A load light will always check integrity AND continuity. A weak light means not enough current going through the wire and a strong light means good wire integrity.
3. So with this said, In order for P0351 to set, the computer has to give an erroneous signal to fire. Pin 7 is an OUTPUT. Now is this caused by a bad computer? Possible. A bad connection? More likely.

Let's face it computers will fail, but in my 22 years of electrical experience bad/loose/dirty connection points are the weakest link. A cold solder joint on the PC board in the computer? Yes, however this will generally show up shortly after the vehicle rolls off the assmbly line. Not 13 years later!
As for the "screw" fix. I read a post from an engineer who scraped all the resin out of the PCM to see what was on the board. The long screws go to a NYLON nut on the board. But does not come near the current path of the PC board.
Attached Thumbnails
PCM.jpg  

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post #28 of 888 Old 01-23-2011, 05:40 AM
ZeeJay1997
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Flyboy, your almost exactly where I am on this problem. Stalling when tapped is a dead giveaway that the PCM is bad. Mine does not stall when tapped. For me it's toss up between the connector and the PCM. Someone on this forum has sourced the pins for the connector. That may be my next move if I cant isolate it to the PCM. I installed a reman PCM in March of last year. It ran great until about a month ago.


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post #29 of 888 Old 01-23-2011, 06:37 AM
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for the record, I have the same issue as the OP. my 97 runs fine then stalls randomly , try to start it and It runs like crap if it does start. all the same codes show up as well ... all I do is now go out and wiggle the PCM and it's connectors and its good to go. well, temporarily that is.
I know it is probably a bad soldier joint but the PCM is Hermetically sealed and I did not dig into the rubberized crap that surrounds the BOard. I inspected the connectors well and sprayed them with electronics cleaner as well as the proper dielectric grease. I know when my son own this jeep he had replaced just about all the sensors till I REALIZED that I could create and or stop the problem by tapping on the connectors/PCM .

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post #30 of 888 Old 01-23-2011, 06:41 AM
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We need someone to manufacture new pcm's. Like that will happen. My last one was installed month and a half ago. Starting to act up. So I guess I need a stack of reman pcms to keep the Grand. Maybe I could install some sort of vending device like in a candy bar machine. I drop$200 in the slot and another pcm falls into place. LOL,try a pcm bar with its nice gelatinous center.
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