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Some more background on the parts cannon diagnostics by the previous owner. I remind everyone that I consider the PO an able mechanic. Like most of us, he is likely much better at mechanical things than electronics.
Hurt my feelings when I became aware that he had purchased a rebuilt PCM off the net and paid, I believe, over $700. My '86 truck's ECM was listed at Advanced for $150. The PO was pretty sure he was dealing with an able and competent supplier. I asked if his supplier had asked about transmission and calibration code. PO confirmed he had. But a few days later a120 pin unit showed up.
I knew he had sent it back, exchanging for a different unit. I didn't realize until the other day that this truck was a 60 pin. Remember, I was pleasantly surprised because I had a 60 pin breakout box.
What I'm getting at is maybe the PO bought from a disreputable vendor. Maybe the PCM is incorrect and junk to boot.
I know the truck doesn't always shift gears correctly so I wonder if there is a E4OD vs 4R70W issue. My truck having the latter. Were '95s mostly 4R70W equipped?
I also know the PO's wife is the one who went to AutoZone to pick up the first ICM (actually, the truck was her's, a hand me down from her father)
How are the terminal ends at your coil connections?
How are your ground connections?
The coil connectors are dirty but corrosion free. I've unplugged and replugged many times during this quest. I'm sure of good connections.
The grounds? I cleaned and shined every ground I could find except I haven't serviced the main cable connections at frame and block. I should. I have checked for non harness ground problems as well. Pick up module to distributor housing. Housing to block. Everything does show <1 ohm resistance back to the battery (-)
I would like to think I have the grounds covered but I can't be sure. Can you suggest where to look for any of those stealth, not easy to find ground points?
I can put my hand on every ground wire, splice, connector and ground lug on my '86 EFI... Blindfolded!
Posts 6 and 7 here is where I'd look https://www.ford-trucks.com/forums/1...nd-points.html
Definitely clean the connections or replace that main ground cable.
I bought a ground cable off the shelf at a brick and mortar parts store, just for it's terminal ends. The connection at the face of the engine block on my '88 5.0 needed a certain shape terminal end.
I also use antioxidant on all my connections.
I put this on every electrical connection I make. (Whatever brand you want).
Posts 6 and 7 here is where I'd look https://www.ford-trucks.com/forums/1...nd-points.html
Definitely clean the connections or replace that main ground cable.
I bought a ground cable off the shelf at a brick and mortar parts store, just for it's terminal ends. The connection at the face of the engine block on my '88 5.0 needed a certain shape terminal end.
I also use antioxidant on all my connections.
I put this on every electrical connection I make. (Whatever brand you want).
@Soup bean you gotta look those new battery cables over good. A lot of junk for sale out there.
The negative and starter cable were store bought. They've been there since 2018.
I made the positive cable out of #2 THHN. Also in 2018. So far, so good. (EDIT: I made the starter cable too.)
Not sure if I reported or even checked this before but with current flowing,when the coil (-) is grounded the current stops. Unground and it starts again... "Most" times. If I poke at the coil (-) I can get the current to stay off... Sometimes.Note, grounding using test light.Bizarre.
That is the key symptom here. An incandescent test lamp is relatively low impedance. Whatever is being induced on the ignition system, RFI/EMI/your favorite acronym, should not be able to get past the shield around the key ignition signals.
The shield is a foil wrap around those key signals and is grounded at only ONE end. A lack of grounding or grounding at both ends reduces the effectiveness of that shield.
Below is a diagram of what I am referring to. Peel back the outer covering then verify that shield is grounded properly Somewhere someone may have a TSB related to this.
Not sure if I reported or even checked this before but with current flowing,when the coil (-) is grounded the current stops. Unground and it starts again... "Most" times. If I poke at the coil (-) I can get the current to stay off... Sometimes.Note, grounding using test light.Bizarre.
This is normal. You're forcing the coil to build up a magnetic field and not letting it collapse, because it's getting a ground, even through you're test light. If the magnetic field is not allowed to collapse, then you will get no spark. I can't explain why sometimes it starts up again and sometimes is doesn't when you poke it.
I take it you haven't tried disconnecting the PIP-in signal at the ICM.
That is the key symptom here. An incandescent test lamp is relatively low impedance. Whatever is being induced on the ignition system, RFI/EMI/your favorite acronym, should not be able to get past the shield around the key ignition signals.
The shield is a foil wrap around those key signals and is grounded at only ONE end. A lack of grounding or grounding at both ends reduces the effectiveness of that shield.
Below is a diagram of what I am referring to. Peel back the outer covering then verify that shield is grounded properly Somewhere someone may have a TSB related to this.
Interesting theory. But what in the circuit would be creating 68,000hz buzz? In my opinion, I believe the PIP in the distributer is faulty and is creating a very low voltage 68khz ripple that the ICM is seeing and amplifying.
That is the key symptom here. An incandescent test lamp is relatively low impedance. Whatever is being induced on the ignition system, RFI/EMI/your favorite acronym, should not be able to get past the shield around the key ignition signals.
The shield is a foil wrap around those key signals and is grounded at only ONE end. A lack of grounding or grounding at both ends reduces the effectiveness of that shield.
Below is a diagram of what I am referring to. Peel back the outer covering then verify that shield is grounded properly Somewhere someone may have a TSB related to this.
Thanks. Worth a try and on my list. I have experience with the shield on my 1986 truck. Intermittent signal loss due to PIP shorting to shield. Also, I am familiar with the TSB on this truck. I have wiggled the heck out of the harness in the problem area per TSB. It's a pain to open the aged, stiff harness but at least it should be easier on this truck. On my '86 the wiring is laying along the intake manifold getting engine heat cooked. Also, my base model '86 was delivered with no protective loom on any harness.
But what in the circuit would be creating 68,000hz buzz? In my opinion, I believe the PIP in the distributer is faulty and is creating a very low voltage 68khz ripple that the ICM is seeing and amplifying.
Very possible, but never saw one failing this way.
Very possible, but never saw one failing this way.
Me neither. But multiple ICMs are having the same problem. So I'm ruling that out. The ICMs job is to amplify the PIP's signal and SPOUT signal. The OP has pulled the SPOUT connector and it's still arcing, so it's not the SPOUT/ECU issue. The only thing left is the PIP.
Cold, wet and windy today so no hands on the truck.
Review: Truck does easily start and run. Did take it for a short spin but that did not go well. Truck lost ability to accelerate. I need to do this drive again to confirm the procedure that brought it back to life.
Idles like many of these trucks do. Smooth and proper rpm most of the time. Will go slow, almost die idle where it may correct on its own or with a pedal blip.
Spark does occur as one would expect. The ignition system seems to do what it is supposed to. The current flow is still always there in the background. This was tested by putting the spark test tool on the distributor cap coil post and watching spark while running. I could always see the current flow in the background.
I know I'm going to check the shield and its grounding. Probably tomorrow, weather permitting.
If I have missed or not acknowledged any suggestions anyone still feels is worthwhile, please remind me. Some of the ideas seem like a waste of time but are nevertheless easy enough to perform. Why not do them.
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