Bad EPROM or ECM???

[White93z34]

alright the water pump on my girlfriends 92' 3.4 Euro was failing in spectacular fashion yesterday, no big deal. I changed it out, refiilled and bled the cooling system down, I was letting the car idle for a good while to make sure the fans cycled properly, and at first they would come on about when they were supposed to but not shut off at all. Then they would come on as soon as the key was turned on but engine off (KOEO)

 

then things got really strange.

-The idle would drop to about 4-500, the lights would get dim as a result. and during this. I could unplug the IAC and TPS with no change in how the car acted.

-No rev limiter in park at all.

-Tried driving it, the speedometer did not function trans started in second gear all the time

-stalled often

-KOEO the ses lamp would come on briefly then go out, not stay on like it should

-no codes set at all

-both fans would run full tilt all the time

- if I shut the car down for a few minutes it sometimes would go back to functioning properly for a short while.

 

Finally I pulled the computer back out and if i tapped on it it would change how the car ran for better or for worse.

 

So I went and picked up a spare ECM I had from a 92' GP 3.4 auto car and put the whole thing in it. and the car ran instantly better and everything functions like it should now.

 

So because I am a packrat I do not want to throw something away that may still be good, and a 9396 ECM is always nice to have around, should I be suspect of the EPROM it had a AYxx code IIRC. and the new one has a code that starts with Bxxx. Or is it more likely that the ECM itself is bad?

[IRONDOG442]

I think the ECM is bad throw it away!

[RobertISaar]

honestly, it could be either... swap the MEMCAL and see if the problem follows it.

[Galaxie500XL]

Is it possible due to the location of the PCM relative to the water pump that antifreeze found it's way inside? If so, it may be possible to clean it with contact cleaner after it dries out.

[White93z34]

I doubt it. I didn't get any mess near it, and it is weathertight. She claims the car is running better now, so who knows maybe its been acting weird for a little while and me bumping it while doing the WP was the final brick in the wall.

[RobertISaar]

here's something i just made... may be useful to you, may not.

 

if there are no notes, assume it's just a run of the mill LQ1 + 4T60E

DF LQ1 interchang.txt

[White93z34]

actually that should be rather useful. I'll be saving that.

[GOT2B GM]

AUX terminal tight? I have a stock 91-93 LQ1 4T60E eprom kicking around here

[White93z34]

that is one thing i didn't touch. but the new ECM seems to have cleared up its issues with life.

[alec_b]

Sounds just like the symptoms I had on a customers base lumina 3.1. Swapped over the ECM (original prom) and it fixed all the problems.