i own a 1984 Fiero with the iron duke in it and i had what at first taught was a fuel pump problem, the car would not start and the pump would not prime with the key on the on position, so i changed the pump and relay, which didn't fix the problem. after some observation i noticed that there was no intial injection from the injector when the key was turned to on (hence no 12v on the green/white wire to the relay) but the gas pump would prime when the engine was cranked. to make the car start i jumped the g terminal on the ALDL to prime the pump and poured some gas into the throttle body and the car started and remained running. after checking the forums for some info, i found out that the ECM controlled the priming sequence and the initial injection, so i order an ecm online and changed the one that was in the car. i opened that ecm and found that some parts of it where burnt, thinking i had finally found my problem i put in my new ecm with my Fieros Prom chip and i still had the same problem, the car still started with gas down the TB though and ran fine but when i did start it the first time with the new ecm, smoke was coming out of the cabin from the ecm and guess what it burnt exactly where the old one had.

here is a picture:




so what i want to know is what causes the ecm to burn out like that and whats on that circuit?
and where can i get the parts to fix up the ecm

thank you

The burnt part is a varistor. It operates by shunting to ground voltage spikes. So the reason that part is burning out again and again is that your alternator is putting out too much voltage, and/or your battery is quite dead or perhaps disconnected.

It shunts (shorts) large short term over-voltages to ground. Yours experienced a long term over voltage. The part itself is only the over voltage control for the ECM. So if you have fixed the problem so the electrical system doesn't over-volt, and if the ECM is still good, you could pull the varistor off of the board and the ECM should run. However if the overvolt lasted too long or was too high it could have taken out the ECM also. Sounds like that is what happened with ECM #1. #2 might be salvageable. You can pull that varistor off of most 80's and early 90s ECMs.

[This message has been edited by phonedawgz (edited 11-18-2013).]

so to test if the alternator is surging i check at the battery if there is above 13v right?

Yeah, that kind of damage is going to start at something like 18v. Did you notice the dash/other lights being quite bright also when the engine was running?

no not at all but i wasn't looking either so i wouldn't be able to tell you for sure

Sadly is 84...
alt and/on wires to alt could kill ECM etc.

why? See my Cave, Alternator Sense
Just a loose starter + terminal can cause very big headaches.

Not just 84 Fiero... most GM cars used same wiring before ~85.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 11-19-2013).]

I burned out my ECM due to a spark plug wire hitting the exhaust.

The car would run very erratic until finally it stopped working and would not run. I had it towed to a shop and was told that the fusible link was burned out and the mechanic "fixed" it by replacing it with a regular wire. Car ran for a few days and started to act up again, finally would not run. Had it towed to another shop and they found that the ECM was bad. They replaced the ECM and I drove the car for a few days. I was looking at the motor and then I noticed that the spark plug wire was partially melted where it was touching the exhaust. So neither mechanic really fixed the real problem. If your ECM is burned out, I would look at your spark plug wires; maybe that is the real problem.

It might be possible that the alternator is the problem. What voltage are seeing? High voltage is also caused by a weak battery that cannot hold a charge.

My ECM burnt up the same way your's did.

I found that the NEG wire going to the starter was fraid and that only a few strands where left. So just like the other guy said, "A loose connection can cause this"