I know there are several other threads here and dozens about the net regarding intermittent/random stalling and all the nightmares folks have gone through trying to kill the gremlin for good. Like others I went through the progression on on '97 4.0 GC, in the process replacing all the usual sensors and such, but as the problem progressed I became more and more convinced the problem was the PCM connections, that all the temporary fixes could be attributed to people plugging and un-plugging their PCMs. I had gotten down to the point where I knew that if I fiddled with the cables I could replicate the problem and I refused to do the "magic screw" repair or the tie-wraps because I believed both of them involved movement of the plugs and cables with temporary restoration only until such time that the cables relaxed to their normal intermittent state and the symptoms returned.
Though there doubtless are situations where the PCM is really bad, I had gotten down to the point where I absolutely knew that if the PCM was not bad it MUST be the cable connections. Having disassembled a PCM I found it hard to believe that the connection pins could have or develop bad solder connections to the mother board given the hermetic sealing involved, nonetheless I decided to order a re-furb from the folks in Davie, FL to rule out the PCM prior to tearing those three plugs apart. When I got the PCM two days ago on Friday I put it in and the car refused to start... no primary ignition at all and that unit was clearly a DOA doornail. Talked to their tech, who couldn't believe it at first because they supposedly check them all before they go out, but putting my old unit back in and starting right up in a flooded state confirmed the kill, so that unit went right back later in the day.
Meanwhile I noticed that my symptoms with the old unit were now even worse and I could recreate a stall event by moving almost any of the cables, so I decided that enough was enough and it was time to deal with the plug problem because it simply could NOT be PCM related.
Upon inspection I noted that the socket connections are NOT simple Molex female as I had been led to believe, but in fact a higher-grade version that uses two gold-plated fingers within the female pin socket shell, and virtually ALL those fingers were in a relaxed, retracted state. I know what these types of connectors look like when new and this was definitely wrong, so the moment I saw that I knew that this was the problem, and it explained all the maddening random behavior and false diagnosis that we all have been going through for so long. This was exactly the type of poor connection that can be affected by the slightest thermal and physical movement, but the question was how to fix it short of getting a brand new harness or three new plugs and splicing them in, or replacing all the pin sockets... a daunting prospect fraught with the threat of misplaced sockets upon reassembly.
I decided instead to reset those finger contacts, the method being to hone a dental tool to needle sharpness, put on my most powerful reading glasses and insert the tool between the socket shell and the contact fingers, one by one. If you are a dentist, watchmaker or have worked with electronics all your life (as I have) you will have the requisite hand-eye coordination and dexterity, otherwise I recommend you talk to your dentist or watchmaker.
Anyway, I did it (photos attached) and all the problems were instantly cured, including a bonus silencing of the constant PCI bus noise I have been getting in my AM radio for the past five years... and a smoother idle. I was having a similar stalling problem with my '96 RAM 1500, and occasionally rough idle, though much more random and I had not determined whether it was really the PCM or a random crossfire those Magnums have been known to have due to spark wire routing. I did the same restoration on that vehicle and not only did it cure the random miss but I got my torque converter clutch back... no more PO 740. My third vehicle is a '96 GC V8 has the PCI bus noise, so I will be doing that one as well when my daughter brings it home from college.
The whole process takes about an hour once you get the hang of it and see how the contact fingers are opposed to each other. Just don't ham-bone it... and make sure you get the right tool for the job. Dentists throw these things out all the time for one reason or another, so it really should not be a problem getting one. Failing that you could use a needle, perhaps a sprung-open safety pin but that would really prove an "all thumbs" operation. The other problem is that with the exception of certain sewing needles most pins have a rather blunt taper, and what you need is a gentle taper that allows you to get behind the finger and then just continue to push the needle in between the shell and the finger to spring it inward. The dental tool I used is gently tapered and due to the "hook" shape allows you to see what you are doing and maintain good control over your movements.
Attached are photos, the first shows the tool being inserted behind a finger contact on a completely finished plug... note that you can see the pair of fingers in every socket. The second photo shows a completed plug next to a "before" plug... fingers visible on the gray one, none visible on the white one. After you do this you will note increased resistance when you plug the connector back in, kinda like snapping in as all those fingers part at once, and my advice would be to leave it plugged in there for the NEXT fifteen years.
For those of you who have been grappling with these random problems I have no doubt that this will be the last repair procedure you perform, and for those about to tackle these issues it should definitely be the FIRST.
A final note - Make sure you disconnect the battery before removing those plugs, and since that will reset the PCM you need to drive for a bit to be sure the problem is resolved... you could still have other issues as the root cause, but this one needs to be ruled out first.
Good luck to you all.
Last edited by InterpreDemon; 03-05-2013 at 06:45 PM..
Reason: Last sentence
Having disassembled an ECM I found it hard to believe that the connection pins could have or develop bad solder connections to the mother board given the hermetic sealing involved,
Nice work. Glad you got it figured out. The 100% solution to each individual problem will always vary. From your point of view, it may be "the real fix", but the work that has gone into figuring the solder joints out should not be ignored. The hermetic sealing is what causes the solder joints to weaken.
In addition to eyeballing the sockets to discern their serviceability, you can also use a Pamona 3561 test adapter as a gauge. If the socket does not hold on to the adapter, the socket is bad.
"The hermetic sealing is what causes the solder joints to weaken."
I don't know, ZeeJay, I have followed your many posts, read through hundreds of others and agree that there may be a chance the PCM could be bad for that or other reasons, but it seems to me that the very first thing one needs to do is rule out these relaxed pin sockets as the cause, and given that the repair takes but an hour or so and costs nothing I cannot see any reason one shouldn't start with this one and go on from there if no joy.
There are just too many reasons that any repair that involves moving, pressing, removing and reinstalling the plugs can cause a poor connection to become temporarily better, and it seems to me that until you rule out these connections as being the root cause everything else is going to be a fool's errand. The plugs in both my similar aged vehicles were in the same condition, doubtless they are on my '96 as well, and I have seen these types of problems in non-automotive environments... those gold alloy contacts lose their tension in a decade or so and until you tighten them up you're just going to be chasing your tail with any further diagnosis.
Might we assume that if the connections are originally at fault, the making and breaking of contact can and will affect the PCM components eventually ?
Semiconductors dont like dirty power. I Do know that the soldering jobs on some of the PCM suck too.
I'm also beginning to suspect the cheap batteries we can buy these days arent helping matters....and once a discreet component is screwed up, it never returns to it's original specs.
I agree, Kermit, which is why I opted to try a PCM before tackling those connectors. About a year ago, shortly before the stalling popped up, I had replaced the alternator and in a senior moment had started the engine up with the alternator and PCM ground (RF engine under coil) only hand-tight. Rather than first shut down I just put the wrench on it and the engine naturally stalled... had to cycle the battery/reset PCM to get it to start back up. For that reason I though there might indeed be some inductive junction damage... besides replacing the PCM was easier.
But if you can move those cables in any manner and cause the engine to stall or miss, my money is on the pin sockets. That 4.0, being a six instead of an eight, has more of a jack hammer idle, especially when loaded down in gear... the TC pulls and "creeps" more than the V8, and the old harness from the engine is not as flexible as it was sixteen years ago when the insulation was new and pliable, so it transmits those pulses to the PCM. That explains why the stalls are primarily at idle, or when putting into gear, in my case going into reverse could do it half the time because it engages it much harder and the engine rocks in its mounts.
... Which just reminded me of something else... I had had this problem much worse last summer before I replaced the customary cracked exhaust manifold. In my case I also had a busted stud I had to replace, but while I had it all out I noticed that my LH engine mount was shot, so I replaced that as well. Thinking back now, the improved performance I had attributed to replacing the manifold was more likely the engine not rocking around as much.
Oh mine wasnt so nice to me. It stalled at 10, 20, 30, 40, 50, 60, or 70 MPH. On an overpass...with trucks on my arse and no road shoulder to pull onto. It stalled in Friday afternoon rush hour traffic in Houston and on Dallas-FW freeways. It stalled in the most dangerous intersection in my home town.
And people wondered why I had heart surgery, knowing I was always so cool and calm when others around me were freaking out.... It was my beloved ZJ !
That's funny I did the same thing last week. After 3 cardone PCM's and no fix I suspected the plugs. pulled them off and did the same thing curved dental pick and all. I've done about 70 miles now and no hiccups yet.
Ten years, 230k miles. Also have a '96 V8 I've owned for 13 years and a '96 RAM pickup for nine years. First Jeep was an '86 Laredo I bought new and kept it going for 14 years, and that was the crappy AMC version... new u-joints every other year, GM V6 that had a loose bottom end from the time it was new. Thankfully some kids stole it and threw a rod a couple blocks down the street, so I was able to buy it from the insurance company for salvage, blue-print up a nice Chevy S-10 truck block replacement from the junk yard and run it for another dozen years before getting the '96.
Do all my own repairs, as I have since I was fifteen. I've experienced most of the usual problems... front u-joints, cracked manifolds & studs on the 4.0, replacing intake plenum plates and bearing inserts on the V8's, electrical gremlins, tranny gremlins and such. No job too big or small, but this one was definitely the most baffling. Was almost at the point of throwing in the towel as so many others have... wife *****ing at me about her bad back and what would happen if she got rear-ended and such. Problem is that she, I and my daughter just love these mid-90s Limiteds.. . really great cars and the parts are dirt cheap. The only thing that will kill them is rust or a collision, and we're all good drivers. Haven't had a car payment since 1990 and I want to keep it that way.
I really didn't want to get rid of the '97 because that is a 2WD that I bought specifically for highway driving... simple drive train that will run forever and nice, light steering like my old BMW. Just love that car, and it would have been a shame to toss it but for a few poor connections.
Last edited by InterpreDemon; 03-03-2013 at 07:40 PM..
Reason: sentence added
The reason I asked is that I had the same theory as you when mine started acting up after 12 years. The PCM connectors had never been disturbed.
The theory that vibrations and multiple matings of the connectors could cause the contacts inside the sockets to spring back is a valid one. It is even mentioned in the FSM, that's why I did exactly what you did when i started having problems and it didn't fix it. I even installed a donor harness for the outboard connector. This is also why I now test each socket when I have an occasion to remove a PCM connector.
I know of at least three more cases with same or similar results. I can give you a line on some new sockets if you need it. Some of the others on this forum will probably send you some of theirs if you ask nicely.
Originally Posted by ZeeJay1997
The hermetic sealing is what causes the solder joints to weaken.
Sorry, let me qualify this statement. The theory is that in some cases, the thermal effects inside the engine bay causes the hermetic sealing to expand and retract, which in turn flexes the board and attributes to the failure of the solder joints . This problem may be exacerbated by a cracked exhaust manifold overheating the engine bay. Also, it is a known fact that some vendors for Chrysler electronics had quality problems.
Originally Posted by InterpreDemon
But if you can move those cables in any manner and cause the engine to stall or miss, my money is on the pin sockets.
Well, time will tell. Like you, these plugs were never touched until recently, at least not since 2003 when I bought the car, and the stalling problem didn't rear its head until last year. All I know is that when I go from replicating the problem by gently moving the cables about, to not being able to cause the error even if I twist them into a pretzel, I consider it progress.
In any event it certainly is the first thing to check, especially if you are getting no codes. The fact that this cleaned up several unrelated issues on two vehicles at the same time tells me all these connections are suspect and gives me great hope, but we'll see what the Gods have in store for me over the coming weeks. I'll keep the thread updated.