PCM issues
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Cross-Country
Joined: Jul 2021
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Status remains the same: no fuel pump activation and ignition is present only when the SPOUT connector is removed.
The engine runs with the fuel pump manually grounded and the SPOUT connector removed.
We are on the 5th PCM and we now have a 104-pin breakout box.
Pins 55, 71 and 97 all have power and all of the grounds are good.
The only thing found bad in the wiring was the wire from the DPFE sensor was broken in the middle and was providing only intermittent connection.
This issue started on Sept 13th. Thank God it wasn't a Friday. >8]
ADVthanksANCE for any hint of something to try to figure this out.
-Jack (refusing to get accustomed to not having a truck)
The engine runs with the fuel pump manually grounded and the SPOUT connector removed.
We are on the 5th PCM and we now have a 104-pin breakout box.
Pins 55, 71 and 97 all have power and all of the grounds are good.
The only thing found bad in the wiring was the wire from the DPFE sensor was broken in the middle and was providing only intermittent connection.
This issue started on Sept 13th. Thank God it wasn't a Friday. >8]
ADVthanksANCE for any hint of something to try to figure this out.
-Jack (refusing to get accustomed to not having a truck)
Logistics Pro
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If you cannot use a DVM, I doubt a breakout box will help.
What is the status of wire/pin #36 when SPOUT is plugged in?
Is it shorted(power/ground) or open?
What is the status of wire/pin #36 when SPOUT is plugged in?
Is it shorted(power/ground) or open?
Last edited by wwhite; Nov 1, 2021 at 04:19 PM. Reason: correction, wrong PIN number 36 not 50.
Mountain Pass
Joined: Dec 2020
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Regarding the photo of the damage on the board of the original PCM (in reply 19), something very catastrophic happened - multiple components were completely destroyed: over (or reverse) voltages and high currents hit all of those components. It would seem unlikely that that wouldn't take something else out in the truck. Since higher than normal currents had to flow to cause all that, have you checked _all_ of your fuses (ctrl-F of this thread has no hits on 'fuse')?
Careful study of that old PCM board and what all got fried might be traceable to one (or more) of the PCM's connector pins, which would be pretty indicative of where downstream to also look. With that PCM destroyed, there's no more harm possible in now pulling the board out so that you can study both sides. Pictures of it posted here would allow us to look at it too.
Where'd you get the 104-pin break out box? Those things are usually pretty expensive.
Careful study of that old PCM board and what all got fried might be traceable to one (or more) of the PCM's connector pins, which would be pretty indicative of where downstream to also look. With that PCM destroyed, there's no more harm possible in now pulling the board out so that you can study both sides. Pictures of it posted here would allow us to look at it too.
Where'd you get the 104-pin break out box? Those things are usually pretty expensive.
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Cross-Country
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BWNG, thanks for the update.
I found the breakout box on eBay, and figured that if my repair guy doesn't want it, I could re-sell it pretty easily.
I'll get the old PCM apart and post images of the carnage.
Kodak plant burns to the ground. No film at Eleven. >8]
I found the breakout box on eBay, and figured that if my repair guy doesn't want it, I could re-sell it pretty easily.
I'll get the old PCM apart and post images of the carnage.
Kodak plant burns to the ground. No film at Eleven. >8]
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Cross-Country
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Also, there's a new clue: the engine will start with the SPOUT out, and continues to run after the SPOUT is plugged in.
The engine will NOT start with the SPOUT in.
All of this is with the fuel pump relay manually grounded.
The engine will NOT start with the SPOUT in.
All of this is with the fuel pump relay manually grounded.
Logistics Pro
Joined: Aug 2014
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Cross-Country
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I only have three remaining, the original and 2 replacements.
Both of the replacements are the 2nd ones from each vendor, as their initial offerings showed all of the symptoms I still have.
Since they both have warranties, I cannot remove the covers to inspect the insides, as this will void the warranties.
I'll see if I can find one for a '96 in a local junk yard to get pictures of the insides.
Both of the replacements are the 2nd ones from each vendor, as their initial offerings showed all of the symptoms I still have.
Since they both have warranties, I cannot remove the covers to inspect the insides, as this will void the warranties.
I'll see if I can find one for a '96 in a local junk yard to get pictures of the insides.
Mountain Pass
Joined: Dec 2020
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Those black clips are holding transistors or such against the metal frame (so that the frame becomes a heat sink; these transistors are probably there to be able to drive something external with more power than the logic circuitry can output) - they're blocking the view of these transistors. Remove these black clips and inspect these hidden components in that fried corner. Can the board be removed from the frame?
The goal is to try and figure out if any of the fried components have a trace that goes to the PCM's connector; poking around with sharp probes on a continuity tester might help with this. The board might have layers of traces sandwiched in between insulating layers, which would complicate achieving this. Can you tell if the board has more than two layers of metal traces - i.e., does it have any layers of metal other than the ones on the top and bottom? You can usually just look at the thin side of the board and tell.
The goal is to try and figure out if any of the fried components have a trace that goes to the PCM's connector; poking around with sharp probes on a continuity tester might help with this. The board might have layers of traces sandwiched in between insulating layers, which would complicate achieving this. Can you tell if the board has more than two layers of metal traces - i.e., does it have any layers of metal other than the ones on the top and bottom? You can usually just look at the thin side of the board and tell.
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Fleet Owner
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From: Easton,Ks
They are for grounding the device they are hooked to.
The only output from a PCM is the 5 Volt reference voltage for sensors.
More than likely the transistors were wired to shorted wires to full battery voltage in the harness or water in the PCM connector.
Mountain Pass
Joined: Dec 2020
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They do not output any power.
Power, 'P' (in watts), equals Volts X Current - https://en.wikipedia.org/wiki/Watt
They are for grounding the device they are hooked to.
Such a transistor could be switching the (power consuming) device's positive terminal to some positive voltage (V) or switching it's negative terminal to ground (or even to some other voltage, like V/2 or -V) - it doesn't matter - it's still the thing that is driving the power to the switched device.
Fleet Owner
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From: Easton,Ks
If they weren't handling power then they wouldn't need a heat sink.
Power, 'P' (in watts), equals Volts X Current - https://en.wikipedia.org/wiki/Watt
Power, 'P' (in watts), equals Volts X Current - https://en.wikipedia.org/wiki/Watt
In other words there is no power leaving the PCM except for the 5V DC reference voltage for sensors.
That was the point I was making.