Infamous Stalling Problem - The REAL fix
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