95 GT PCM issue?

weendoggy · Jan 2, 2025

95opal said:
Before you go hog wild on a PCM issue. Did you pull the codes? What you describe sounds like a vac leak or possible TPS issue.

I think the EEC-IV isn't as good as the newer systems. You can't "pull" codes from them. It's a lot of backtesting circuits and the like. To do it a bit better, you need a Break-out-Box that you probed with jumpers and read voltages etc. I used one with my OBDI OTC tester and doing KOEO and KOER tests and the infamous, wiggle test. One thing on the ECU is the capacitors go bad, especially with age. Again, not saying the ECU is bad as most arent'. You really have to know the system and diagnose it the old way.

RatFink · Jan 2, 2025

New distributor made no change today. Removed the PCM and pulled it apart. Found 2 capacitors that had leaked out. Had to buy a pack of 50 to get 2. I'm going to try replacing the bad onesandd see what results I get. If this doesn't fix the problem, I'll more than likely order a Megasquirt system. I'll probably order one either way, I'm just hoping this buys a little time.

RAU03MACH · Jan 2, 2025

exact reason why i am hanging on to the EEC STAR TESTER
when i brake that thing out people are tripping
you would not believe how much that old unit brings in and how many people have that old system

RatFink · Jan 2, 2025

RAU03MACH said:
exact reason why i am hanging on to the EEC STAR TESTER
when i brake that thing out people are tripping
you would not believe how much that old unit brings in and how many people have that old system

Probably a good call!

RAU03MACH · Jan 2, 2025

back in the day that was the shit for keeping up with ford engines
i got one of those handed to me at ford quite a few years back as a tech

RatFink · Jan 16, 2025

Thought I'd update on my situation. Finally replaced the capacitors in the PCM and got it to fire back up. After this it would barely idle. It was like it was "searching for the idle" but couldn't figure it out. Replaced the TPS and that resolved the issue. Went for a drive and still have crazy loud popping from the exhaust. I'm afraid the PCM may have damage other than what was visible. That's the only logic I can come up with. 2 distributors, nearly every common sensor replaced, quadruple checked timing, etc. I will say, when I pulled the PCM I was able to check out the "tuner" I previously mentioned and it looks to be a Bama. I guess there's a chance that's what giving me issues?

GTamas · Jan 17, 2025

RatFink said:
Thought I'd update on my situation. Finally replaced the capacitors in the PCM and got it to fire back up. After this it would barely idle. It was like it was "searching for the idle" but couldn't figure it out. Replaced the TPS and that resolved the issue. Went for a drive and still have crazy loud popping from the exhaust. I'm afraid the PCM may have damage other than what was visible. That's the only logic I can come up with. 2 distributors, nearly every common sensor replaced, quadruple checked timing, etc. I will say, when I pulled the PCM I was able to check out the "tuner" I previously mentioned and it looks to be a Bama. I guess there's a chance that's what giving me issues?

Have you checked for vacuum leaks with a smoke machine?

RatFink · Jan 17, 2025

GTamas said:
Have you checked for vacuum leaks with a smoke machine?

I have not.

ttocs · Jan 17, 2025

backfiring would mean too much fuel though wouldn't it?

RatFink · Jan 17, 2025

Another update. I removed the chip from the PCM and the backfiring stopped. It also idles with a more consistent "chop". I'm finding now the car wants to surge in O/D and wants to die when I put it in gear. I have to drive with 2 feet to get it rolling. I can stop and go ok, but the initial load from P to D kills it without both feet. I'm assuming the tune the chip contained helped offset the cam. My thoughts are to order another PCM since I put bandaids on this one, and just have another file made to a new chip. I realize this is primitive, but I'm a primitive guy. Thoughts and input are welcome.

ttocs · Jan 17, 2025

your running it now with no chip in it?

RatFink · Jan 17, 2025

I drove it a few miles without the chip and have not put it back in.

ttocs · Jan 17, 2025

leads me to think it is in the tune. I got one from bama YEARS ago after a HCI swap and it ran horribly from them. I limped it to a dyno and got it tuned and it ran great from then on.

RatFink · Jan 17, 2025

Assuming you've read the thread and are familiar with all the problems I posted, do you think I'm on the right track with replacing the PCM with a fresh one and having a tune written on new chip? I really can't wrap my head around what caused so many failures at once. I get the car is old, and maybe it's just that. But to go from a perfectly running car to a bad distributor, bad TPS, and a PCM with bad capacitors is just kind of odd.... or at least it's odd to my somewhat simple brain.

RAU03MACH · Jan 17, 2025

id say new pcm for sure
and a tune that is possibly burned up as well and it was tuned for whatever mods have been done

ttocs · Jan 17, 2025

I would try a new tune before I did the pcm.

RatFink · Jan 17, 2025

I appreciate the replies and input from everyone. I'll post updates as I progress. Who knows, maybe it'll save someone some headache down the road.

RatFink · Feb 25, 2025

I know this post has sat idle for some time, but I thought I'd post an update. I got the new PCM/ECU installed. Tried running it without the piggyback tuner and was having some very odd idle issues like being stuck around 700 rpm's and sounding like an old carberauted truck to jumping to 1500 and holding there. Another issue was driveability stuff like the transmission shifting funky. Finally, I pulled the ECU and put the piggyback back on. Idle is strong, and holds steady around 1k. It's funny that with the tuner the cam sounds much bigger (very choppy) than without. Only issue now is it will occasionally stutter, jump rpms for a second, and then go back to a steady idle. Overall it's nearly back to normal, I just have trust issues with it at the moment.