The ECM, from what I hear, RARELY goes bad.. So I ignored the ECM and spent the whole week chasing wiring down in the car with no results. In frustration, I plugged in an ECM from a '90 S-10 and my problems go away. Here's what the old ECM is doing..

The fuel pump does not come on via the relay when I turn the key on but the oil pressure switch will turn it on and I can jumper the pump to make it run. There is 12V from the ECM to the relay when I turn the key on (and does not drop to 0V after 2 seconds) UNTIL I actually plug the wire into the relay, at which point it drops to 0.7V - not enough to close the relay and turn on the pump.

The ECM also runs in low voltage mode, causing it to idle at 2000 RPM. According to the scan tool, the ECM thinks it's got 12.2V when I measure 13.9 across the battery terminals.

So the solution is obviously to find a new Fiero ECM and hook it up, but what made it go bad? I've got 2 ohms of resistance between the fuel pump wire and ground at the relay. I don't know if this is too little resistance, pointing to a short in the pump or a bad pump that's frying the ECM - in which case, I should fix the problem rather than throw ECMs at it.

I've owned the car for 13 or 14 years and the problem has been going on for so long, I don't even remember when it happened. BTW, it's an '85 SE V6 but I doubt that matters. I did have to take out the door ajar dinger many many years ago because it wouldn't shut off, but I can't find a short in the system.

Any opinions on the cause of the damaged ECM before I fry a replacement?

And, BTW - a jumper between the cig lighter and terminal G in the ALDL makes the pump run fine. I popped the Fiero ECM open and there are no apparent burns on the circuitry, although the tracings on the board are all wrinkled. Guess that means it must be old?

I've read here that the '85 ECM is different than other years. Does that mean an '86 V6 ECM won't work? What if I wind up with a 4 cyl. ECM - can I just change the EPROM and CALPAK?

Check the green wire at the fuel pump relay for +12v when you turn the key in the run position.

There will only be power there for 2 or 3 seconds untill the engine starts up.

I've seen several 2.8 ECMs burn up the transistor in the fuel pump circuit.

The 4 banger and V6 ECM are not interchangeable, but a 85 V6 ECM will work on your 86. Just use the EPROM and CALPAK that come with the 85 ECM.

[This message has been edited by jelly2m8 (edited 09-06-2003).]

Thanks, Jelly. The green wire at the relay has 12V when I turn the key on, but it's constant as long as the key is on and the relay is disconnected. As soon as I connect that green wire to the relay itself, the voltage drops to 07.V...

Do you know the location of this transistor on the board? I could just replace it and see what happens. Transistors are cheaper than a new/used ECM.

quote Originally posted by jelly2m8: The 4 banger and V6 ECM are not interchangeable, but a 85 V6 ECM will work on your 86. Just use the EPROM and CALPAK that come with the 85 ECM. [This message has been edited by jelly2m8 (edited 09-06-2003).]

Hey Jelly, did you mean to say 86 V6 ECM will work on your 85 and to use the chips from the '85? I have an '85 SE, not an '86.

With the ECM reporting 12.2 V in addition to this problem, I'm really wondering if it isn't a short in the system causing this. Anyone know which wire into the ECM is used to read the battery voltage? If I could test that one, I could verify if the problem is inside or outside the ECM.

Jelly2m8,
I did not know the ECM was different on some years. From what I read in this and other threads, the 85-86 V6 are interenchangable and 87-88 V6 are interchangable. Now I wonder what is different. I had a spare V6 out of an 85GT that I stuck in my 87GT so I could drive the car while refreshing the 87 V6. The 85 motor runs great except runs rich. I assumed it's because it's an old engine with 153k miles. So the question is are the engines affected by the different years? Should I also be doing the same as STINKIN_V8 and switch to a 85GT ECM? That's interesting.

bump to keep it alive for viewing by others.

I've got the exact same problem('86GT), i'm waiting on my new ecm to arrive(should be here saturday), i'll let u know if it works, i have replaced everything else(relay, fuel pump-which went bad, ..jim

Forget who posted this the first time but when your done go to file and save as, save to your hard-drive.
http://www.cruzers.com/~ludis/fieroprom.html

HTH

Have you checked the dk grn/wht wire from ECM to Terminal A on fuel pump relay for a short to ground? it appears when you hook the green wire back up to terminal A, it loads down the ECM. I must say however, that your ECM swap pretty much proves the ECM is bad.

------------------
Tim
Red 88 Formula Auto
Stock 2.8 100K+ Miles
Hypertech Thermomaster
NoCat NoEGR

As stated above, i had the exact same problem, i just swapped out ecm's, and the problem is fixed!!! Hope this helps..Jim('86GT)