Computer repair advise

sammie9271 · Jul 28, 2025

Im trying to help my neighbor get a mustang going he inherited from his buddy after passing away. The car died one day and never started again. KOEO the check engine light never comes on. When the diagnostic port is jumped the check engine light come on and stays on (never flashes). I verified power and grounds at the ecm were good. I pulled the computer out and opened it up to find what I belive is a blown resistor that connects to the first mosfet closest the the failed component. Any suggestion on if I should do for repair would he appreciated and hopefully somebody knows what this part is so I can order a new one. Thank you for your time!!!

91AOD5.0LX · Jul 28, 2025

Home - ECU Exchange

ECU Exchange specializes in the re-manufacturing and repair of engine control modules.

www.theecuexchange.com

thatblackfoxbody · Jul 28, 2025

Have not seen a PCM fail like that before. A short somewhere could have done it. Got a picture of the bottom of the board to see the resistor component legs? Swapping the computer for a refurbished one may be a good move, but a repair could be cheaper if you already have the tools.

Shakerhood · Jul 28, 2025

Mine has been getting rebuilt at ECU Exchange, just got the report and tracking number for its return earlier today, it had a lengthy list of failed components needing replaced according to them.

sammie9271 · Jul 28, 2025

I have good soldering equipment and feel comfortable replacing anything recommend just to try but I see one leg goes to the closes mosfet but the other leg i can't see any connections making me think this board has two layers... I took a picture of the backside and pointed a pen at each leg. I guess start by removing and testing the mosfet?

sammie9271 · Jul 29, 2025

thatblackfoxbody said:
Have not seen a PCM fail like that before. A short somewhere could have done it. Got a picture of the bottom of the board to see the resistor component legs? Swapping the computer for a refurbished one may be a good move, but a repair could be cheaper if you already have the tools.

I posted the response below on the thread hopefully that works.

General karthief · Jul 29, 2025

Do you have the ability to test the computer components (and the knowledge)?
Just send it off to the Exchange and they will check out all the stuff and update needed components.......easey peasey.

Noobz347 · Jul 29, 2025

It looks like either a hard short or the EEC got a polarity reverse.

Either way, I would send it in. Replacing components is one thing and the ability to test it afterward is another.

sammie9271 · Jul 29, 2025

Noobz347 said:
It looks like either a hard short or the EEC got a polarity reverse.

Either way, I would send it in. Replacing components is one thing and the ability to test it afterward is another.

Any recommendations on somebody I can sent it to that has a quick turnaround time?

Noobz347 · Jul 29, 2025

sammie9271 said:
Any recommendations on somebody I can sent it to that has a quick turnaround time?

91AOD5.0LX said:
Home - ECU Exchange

ECU Exchange specializes in the re-manufacturing and repair of engine control modules.

www.theecuexchange.com

We've had lots of dudes send their EEC to these guys and so far, so good.

When I find my round-tuit, I'll be sending mine in for a refurb and to my knowledge, there's nothing wrong with it.

gkomo · Jul 29, 2025

+1 on ECUExchange. I've said it throughout many threads, but nothing was seemingly wrong with my ECU, car ran fine, no issues. Sent it out to ECUExchange just for piece of mind (since unknown condition of ECU and they are old now) and they found many things 'wrong' with it and fixed the issues they found. I'd send a Fox ECU in even if I had no discernable reason to.

sammie9271 · Jul 29, 2025

Noobz347 said:
We've had lots of dudes send their EEC to these guys and so far, so good.

When I find my round-tuit, I'll be sending mine in for a refurb and to my knowledge, there's nothing wrong with it.

Your the man! Thank you for your help

pats91 · Jul 29, 2025

I'll throw in my recommendation for ECU Exchange. The turn around wasn't too long.

General karthief · Jul 29, 2025

sammie9271 said:
Your the man! Thank you for your help

Ahhhhh, I've sent a half dozen of them to EcUExchange, maybe more, how many laptop or desktop computers are still in use in original condition? Fones too for that matter.
Diodes, transistors, transformers have all evolved, bigger, better, faster, more.

crappy pic but those are computers from 1999 thru 2015. Now you have a computer in your hand, our junk is the FIRST generation of automotive computer control.
send it in, piece of mind.

revcor · Jul 30, 2025

gkomo said:
+1 on ECUExchange. I've said it throughout many threads, but nothing was seemingly wrong with my ECU, car ran fine, no issues. Sent it out to ECUExchange just for piece of mind (since unknown condition of ECU and they are old now) and they found many things 'wrong' with it and fixed the issues they found. I'd send a Fox ECU in even if I had no discernable reason to.

If you don't mind sharing, what specifically were the issues they found and corrected? The idea of issues that were physically present, but hadn't yet manifested in how the engine runs, perhaps because they become relevant only under certain conditions not yet experienced, or were caught when their effect on running was so slight it wasn't yet noticeable, etc. etc. is very interesting to me. It's like finding and treating a health problem in a human that'd been silently waiting to kill ya

91AOD5.0LX · Jul 30, 2025

revcor said:
If you don't mind sharing, what specifically were the issues they found and corrected? The idea of issues that were physically present, but hadn't yet manifested in how the engine runs, perhaps because they become relevant only under certain conditions not yet experienced, or were caught when their effect on running was so slight it wasn't yet noticeable, etc. etc. is very interesting to me. It's like finding and treating a health problem in a human that'd been silently waiting to kill ya

This is what they sent me via email when my computer was repaired a few years ago.

Shakerhood · Jul 31, 2025

91AOD5.0LX said:
This is what they sent me via email when my computer was repaired a few years ago.

Mine had quite an extensive list of items they had to repair, including the power supply like yours, its been about 3 weeks since I shipped it and its due back here on Saturday.

rednotch · Aug 1, 2025

Keyworksecu in VA only place I'd recommend for stuff I'm not willing to do myself. No canned generic, we replaced something that doesnt exist replies. He has plenty of videos repairing old ford eec iv's, many others wouldn't or couldn't fix. More know for the trucks ecu's though, he charges $150 for the fox body ecu's View: https://www.youtube.com/watch?v=R7sQrWtes8I

That's usually an over voltage issue, I'd check for more issues than just that if you plan on repairing it yourself, betting its not the only failed component..

Parauno · Aug 2, 2025

sammie9271 said:
Im trying to help my neighbor get a mustang going he inherited from his buddy after passing away. The car died one day and never started again. KOEO the check engine light never comes on. When the diagnostic port is jumped the check engine light come on and stays on (never flashes). I verified power and grounds at the ecm were good. I pulled the computer out and opened it up to find what I belive is a blown resistor that connects to the first mosfet closest the the failed component. Any suggestion on if I should do for repair would he appreciated and hopefully somebody knows what this part is so I can order a new one. Thank you for your time!!!

I would contact Fox Mustang Restoration in Locust, NC. They specialize in ECM rebuilds.

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