is this just from age or is something else going on?

The ECU most likely just failed, as electronic parts do after time. You really can't say for certain though whether it was age or something else. Had you made any changes to the car recently?

two days before i just did new plugs and wires

it looks like something has shorted out in the ecm. the burn marks are pretty bad

Test alternator Before you replace ECM!
Test alt wiring. Sense Wire is good and plugged in tight?
Physically follow sense wire from plug for alt to splice in alt output wire.
Do a long test and make alt hot.

Or just replace alt... Cheap insurance.

If sense wire, plug in terminal, splice (S501), alt output wire, and/or regulator is bad then you have a bigger problem...

Sense wire name matters.... (Pin A on SI alt, S pin on CS alt) Very Long story, short on time.... Not in Cave... (electronic folk, think Remoter Sense on Bench Power Supply.)
Sense wire or regulator goes fubar then alt output can go into major over volt, even for a sec or two at a time, and unless you read dash gauge all the time, you can burn thing up.

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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 01-09-2011).]

I agree with Orge on that sense wire. You may to cut off the old and put a new connector on it and clean the connector on the alternator good.

Hmmnm, kinda looks like the ECM voltage regulator. A battery short to reference voltage can cause this.

(160)23266 is a driver chip. (Part # is not burn on image 3 above) I think it's IAC driver. Need U# (Think U16 in many ECM type) and EMC type to see what it drives to be sure.

If so then check IAC and Wiring harness to IAC very carefully.

------------------
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...)

TCC solenoid short

IAC or fuel pump relay short perhaps

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Scratch the TCC solenoid - PROM is for an 84 Manual Transmission

[This message has been edited by phonedawgz (edited 01-09-2011).]

Get ECM Diagrams here... http://web.archive.org/web/....cruzers.com/~ludis/

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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...)

Yes, that particular chip is the IAC motor driver. If I were to guess, I would say that the IAC motor chip failed internally. Like some amplifier chips, they can fail in a manor where it is attempting to put out two opposite polarities to the same two wires, effectivly shorting it out, and that should cause about that level of destruction. If the IAC's wires are shorted it could also do that. So definitely check your IAC wiring, and replace the ECM. Other then the alternator's diodes failing (which can cause the Alternator to pump a particularly nasty A/C waveform into the cars DC circuits) there isn't really much else that can cause the IAC driver to fry up like that.

Hopefully your Prom chip survived.

Ok thanks alot, this gives me somewhere to start looking i forgot to tell you guys that it's out of an 84 with about 160,000 miles on it. I was driving at around 75mph at just about the end of a 40mile drive when it failed. it was an automatic shut down. what caused me to look for the ECU was that when i was trying to get it restarted i noticed no sound coming from the fuel pump. then all of a sudden it turned on and would not turn off even with the key out of the ignition it was still pumping then that's when i noticed the dreaded circuit board burn smell coming from the console. And this is what i found.

so i got the new ECU in and as i was doing a pre-start inspection i noticed that the smaller wire at the positve battery terminal (there are two one large going to the starter and one small going to ???) was completely fried... apperently it has gotten so hot that it burned free from the terminal, melted the insulation on it's self and the wire loom covering it. What does it go to?

IIRC, it goes to the power block by the C500 behind the battery. This is where the red charging wire from the alternator connects. Also the fusable links, etc. I moved my battery up front and moved mine around so I'm a little rusty. Anyone else?

Sorry I don't know the name of it, but there is a small black unit, kinda looks like two black boxes near the battery. That wire bolts down just below that.

Edit: I now see that it's an '84... totally different beast when it comes to power distribution... sorry.

[This message has been edited by Bloozberry (edited 01-17-2011).]

quote Originally posted by fierofinder: Sorry I don't know the name of it, but there is a small black unit, kinda looks like two black boxes near the battery. That wire bolts down just below that.

His car is an 84, the starter motors stud acts as the main positive junction for the fuse-able links. It doesn't have the positive junction near the battery.

Those two fuse-able links supply power to the whole car. If something fry's in the electrical system that is not connected to the fuse panel, it will fry the link instead. When the computer fried, it would likely cause the link to fry. The ECM has no fuse for its power, but it does have a fuse for the signal to tell the computer to power on. I'm not surprised that you found one fried at all.

The burned part in the second picture posted is a Metal Oxide Varistor, which is there to protect the ECM against overvoltage transients on the +12 volt supply. Varistors are sacrificial in operation, but they will still last a long time protecting against fast, short-duration voltage spikes. It seems pretty likely that whatever happened involved a prolonged high voltage condition on the car's +12 volt bus. The most likely culprit would be that the voltage regulator in the alternator failed, shorting +12 volts to the field winding. Even "12 volt" automotive alternators can produce well over 100 volts under such conditions if the engine rpm is high enough. A prolonged +12 volt overvoltage would also explain the fried voltage regulators in the ECM.

Any chance that you ran the car with the battery disconnected? That can do it, too.

[This message has been edited by Marvin McInnis (edited 01-17-2011).]

quote Originally posted by awestfield: so i got the new ECU in and as i was doing a pre-start inspection i noticed that the smaller wire at the positve battery terminal (there are two one large going to the starter and one small going to ???) was completely fried... apperently it has gotten so hot that it burned free from the terminal, melted the insulation on it's self and the wire loom covering it. What does it go to?

Leave that wire off but hook up everything else. Then see what doesn't have power. Then post what isn't powered on here, and I will return a post with what is powered by that wire.

Before doing that you need to take a look and make sure that wire isn't melted into the other wires of the harness.

You said the fuel pump came on by itself. That really indicates the melted wire cut into other wires. You NEED to pull your harness apart and pull the melted wire and replace it and fix any insulation of other wires before you power things back up.

Unless you really want to light your Fiero up.

[This message has been edited by phonedawgz (edited 01-17-2011).]

quote Originally posted by Marvin McInnis: The burned part in the second picture posted is a Metal Oxide Varistor, which is there to protect the ECM against overvoltage transients on the +12 volt supply. Varistors are sacrificial in operation, but they will still last a long time protecting against fast, short-duration voltage spikes. It seems pretty likely that whatever happened involved a prolonged high voltage condition on the car's +12 volt bus. The most likely culprit would be that the voltage regulator in the alternator failed, shorting +12 volts to the field winding. Even "12 volt" automotive alternators can produce well over 100 volts under such conditions if the engine rpm is high enough. A prolonged +12 volt overvoltage would also explain the fried voltage regulators in the ECM. Any chance that you ran the car with the battery disconnected? That can do it, too.

A few weeks earlier i was having issuses with a bad ground. when i wouild hit the brakes i would loose so much voltage that the radio would turn itself off till the alt caught up with the power drain... This was the main ground wire coming from the battery.... this condition went on for about 2 - 3 weeks till i could finally find the problem.... this has been my daily driver for the past year at about 80 miles a day

ok got the new ecu in.... i traced the burnt wire back and it lead to the alternator.... i disconnected all wires from the alt. went to start and the injector started dumping mass amounts of fuel. as played around with it more i realized that any time the vehicle is on the injector opens with no cycle so it is spraying anytime the fuel pump is on.... once loaded with gas the car will run until all the gas is burnt off (fuel injector disconnected of course) any ideas?

Test alt and alt wires very carefully...

See cave. Alternator Sense in charge & start section. article is new.... See help if it won't show up.

84 has a major wiring change is an understatement by far....
Where you blow fuse link A, the alternator run in major over volt condition can fry ECM, Radio, etc. It's not just Fiero "problem," Most GM vehicle before 85ish models have same issue.

1. Fix burn up wiring and any exhaust leaks if any.
2.Trace/Fix ECM wiring harness
3. Move wire goes between A and S501. Make it look like 2nd image in alt sense article. You can move to alt's output directly.

"New" ECM maybe bad. Injector signal, ECM switch to ground on injector. Most likely? Short in wiring, short in injector, or bad ECM.

------------------
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 01-30-2011).]