Electrical Why does my fox body keep frying eecs

[brandyn200]

I have a 1990 mustang gt 5.0 with a 5 speed it had a chip in the eec but from my investigations I have found the the engine is stock

New distributor with pip and tfi only year old
new ignition coil with plugs and wires
new fuel pump
I have been having problems now for 2 years
The first time the car was still running and driving fine but I had codes that would not go away I ended up narrowing it down to the eec being bad

Replaced it car was great drove it as my daily all summer no problems until one morning go out to leave for work car wouldn't start had spark but fuel pump and injectors weren't working

I looked through all the wiring and couldn't find any shorts or bad connections looked at all the fuse able links.

I just put the eec back in after getting rebuild again I thought maybe the chip was causing it and tried running it without the chip and didn't even make it out of the garage and same thing fuel pump won't prime and injectors arent pulsing.
eec doesn't even seem like it's booting up since I'm not getting the CEL when I turn the key on.

Am I missing something obvious or do I really have to dig into this thing more.

Thanks

 

[JMG9350]

Have you checked the ECU ground wire near the battery?

 

[brandyn200]

Have you checked the ECU ground wire near the battery?

Yes it is intact and clean
I've also ohmed out all the grounds at the eec plug and they all come back with less that 1 ohm to the frame
Im thinking there has to be a short somewhere but it's not a dead short since the car was running but as soon as I drove the car even a couple feet it shorted out somewhere and fried it?
I just don't know where to start looking since it isn't consistent

 

[AeroCoupe]

Who did the repairs to the ECU?

 

[rednotch]

How or what is failing in the ecu will tell you more. I remember back when I had to explain when t5 swap cars would burn up 5spd ecu because of the wiring difference between the cars from the factory and people argued for years nah man it's works fine lol. Too many monkey see monkey due repair shops especially with these cars that will give you some stupid canned repair quote when all they did was recap the board and repair a broken trace or two.... Find out what's failing and look at the circuit.

 

[Mustang5L5]

Was this car always a 5-spd?

Two things I'd check. I'd physically look at the O2 jumper and verify it's correct for year/transmission. And then i would put a DMM on pin 46 and check for voltage to ground during key on, and crank. You can do this with the ECU unplugged.

 

[brandyn200]

Cardone rebuild the eec the last time I didn't get a report back on what was wrong. I'm going to send it out to ECU exchange this time so I know what component is failing or why it's not working

I can't see any physical damage to the circuit board or any of its components on any of the eecs that I've had problems with.
No burnt traces, leaking capacitors or anything that stands out so I'm not sure what is failing just the symptoms that I listed before

I will look at the car more tomorrow and check the things that have been mentioned

 

[brandyn200]

How or what is failing in the ecu will tell you more. I remember back when I had to explain when t5 swap cars would burn up 5spd ecu because of the wiring difference between the cars from the factory and people argued for years nah man it's works fine lol. Too many monkey see monkey due repair shops especially with these cars that will give you some stupid canned repair quote when all they did was recap the board and repair a broken trace or two.... Find out what's failing and look at the circuit.

I will mention that I'm not sure if the wiring was replaced or just repaired but it is labeled with a paint marker not sure if that could cause issues or not from what your saying sound like it could

 

[AeroCoupe]

Salvage yards typically mark parts with paint markers.