PCM shorting

Jomax · Jan 7, 2015

Early 99 truck 280k 7.3 4x4

Truck was converted to a dpc-422 pcm family when 250/100% injectors were installed. Truck ran great for 10k miles, so I don't think it was was installation.

First chip was a dp F6, second one was a F5

Truck died driving to CA with the first chip and pcm, cut out and died like a cps. Chip light went out. After unplugging the chip truck still wouldn't start. So I had my brother bring me my spare pcm same pcm family. Installed it and drove it 60 miles home on stock splitshot tuning...

Truck sat over the new years week and i just installed the chip this tuesday. Drove it 500miles and now the second pcm and chip are shot same symptoms..
Sucky part is those pcms are hard to find...

Anyone have this kind of problem? Any schematics of the wiring for the pcm? What values should I be seeing?

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Arisley · Jan 8, 2015

Sounds like a bad chip killed the PCM.

Jomax · Jan 8, 2015

But two bad chips in a row?

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Arisley · Jan 8, 2015

I see what you are saying now. I would check the PCM relay, they go out like that sometimes. One of those relays in the under hood fuse box. Swap with the blower relay for testing.

dzldoctor · Jan 8, 2015

I would check the EBP sensor I have had them take down the 5 volt reference acting like a bad PCM.

Jomax · Jan 8, 2015

But why would swapping in a new pcm fix it? Sorry, i suck at electrical. But if the ebp was bad or a relay. Wouldn't installing a new pcm do nothing?

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Arisley · Jan 9, 2015

When relays go bad, they will sometimes work after removing power to them. They typically fail intermittent.

Sometimes you can make them work by unplugging them and plugging them back in. I carry a spare relay in my glovebox, right next to my CPS.

dzldoctor · Jan 9, 2015

Jomax said:
But why would swapping in a new pcm fix it? Sorry, i suck at electrical. But if the ebp was bad or a relay. Wouldn't installing a new pcm do nothing?

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Technically yes, but if it relaxed or was an intermittent thing maybe enough time went and the "new" pcm fixed it for a bit. Does it communicate with scanner?

IdahoF350 · Jan 9, 2015

If you eliminate the relay and EBP, I would also check the switch and wiring between the switch and chip, if there is a fault, internal short, or short to ground in either of those there is a possibility it could kill both the chip and the PCM simultaneously.

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Jomax · Jan 9, 2015

IdahoF350 said:
If you eliminate the relay and EBP, I would also check the switch and wiring between the switch and chip, if there is a fault, internal short, or short to ground in either of those there is a possibility it could kill both the chip and the PCM simultaneously.

Sent by my right thumb!

New wire was put in with the new chip and pcm. I'm looking into it tomorrow. I'll let you guys know what I find

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Jomax · Jan 9, 2015

dzldoctor said:
Technically yes, but if it relaxed or was an intermittent thing maybe enough time went and the "new" pcm fixed it for a bit. Does it communicate with scanner?

Does not communicate with the scanner.

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Jomax · Jan 10, 2015

Well, swapped in a new relay and she fired up... now the first chip did fry so maybe this was coincidence that this happened right after.

I don't thing a relay could fry and pcm or chip.

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mikes02ls1 · Jan 10, 2015

For it not communicating with scanner check to see if ur cigarette lighter fuse is burnt out. They run off the same fuse

Jomax · Jan 11, 2015

Relay fixed it. I'll know 100% it was the relay after I hit the 1,000 mile mark, till then, everytime I drive it, i worry it'll die. I hate electrical gremlins.

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Arisley · Jan 11, 2015

Good deal on the relay.

Jomax · Jan 11, 2015

If it were really a short, it should've started, correct? Is it possible the IDM is an issue?

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Jomax · Jan 12, 2015

Well, I'm about to light this thing on fire, died on me again. Now stuck on the side of the freeway. Pcm not getting power again... it has to be a contact loosing contact or something...

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Arisley · Jan 12, 2015

I had that issue for a while. Clean the contacts where the relay plugs in. I used contact cleaner and a trimmed up emery board. Use a little pair of needle nose to tighten the contacts back after cleaning.

IdahoF350 · Jan 12, 2015

Also check you main, engine, IDM and PCM grounds.

Sent by my right thumb!

Jomax · Jan 13, 2015

I think I found my issue, two cut wires, no idea how though... after connecting them, pcm and chip powered on. Weird part is, if I disconnect the wires, pcm and chip are still on. It's almost like it takes the pcm a while to notice thus turning off after 80 miles... wires are coming out of the middle right plug (four plugs on fender liner coming from chassis and splitting off) soldering them back and hoping for the best. Fingers crossed!

Also, no codes after it powered back on...