85 GT Struggling for/Losing Power or Throttle not engaging? (Page 1/3)
CZSeventyFive DEC 12, 09:32 PM
'85 GT.

Issue I've been having for a while, could still be fuel pressure or oil pressure? Anyways, I have an '85 GT that seems to be struggling for power, namely when you get to around 3k RPMs or if you just flat out hit the pedal to the floor (it lurches, essentially). What it feels like is that when you reach a certain point with the pedal, the throttle (?) seemingly disengages and no further power gets sent to the car, like the engine audible shuts off(ish) and chokes a bit. If you release the pedal, you can feel the moment that the engine re-engages, and if you're slow with the pedal you can kinda creep past it, although it will inevitably begin to choke again, at which point the gas pedal seemingly turns into another brake pedal.

Similar happening have been going on for a while, and initially it seemed like a fuel pressure issue. Gaskets were replaced, new fuel pressure regulator (which admittedly was installed wrong the first time then reinstalled correctly), some O2 sensors and a fuel filter, and ultimately the fuel pump. After the pump the Fiero ran great for a couple months before getting to the same old. I started to think it was electrical or related to a sensor or the computer. Eventually the alternator showed notable signs of failure, so a new alternator and belts were installed, and due to seeing arcing between the spark plug wires, new wires were installed as well. It seemed to run a better for about a day, with highway speeds once again achievable. Since it seemed like an issue with the throttle, I ran a couple theories by a mechanic friend (who suggested the spark plug wires replacement), and we theorized that a new TPS was due. So I installed and spliced that in, but it didn't improve much of anything.

I'm about to get it into an actual mechanic shop maybe (either for just a diagnosis or a diagnosis and repair), but I'm still trying to figure out what I can do myself. The only repairs that seemed absolutely necessary were the fuel pump for the bad pressure and the alternator since the battery wasn't charging. It's a bizarre jigsaw puzzle, for sure lol. Just thought I would have figured it out by now.

Open to any and all suggestions. I'm thinking it could still be electrical, but is that the correct avenue of thought or am I looking down the wrong rabbit hole?
Patrick DEC 12, 10:03 PM
You appear to have thrown a lot at a fuel supply problem, but I haven't seen any mention made of the actual fuel pressure readings.

[EDIT] Looks like we've been down this road previously.

[This message has been edited by Patrick (edited 12-12-2021).]

CZSeventyFive DEC 13, 05:40 AM
Oh yah. Forgot about that one. I'm not sure why I said I had a pressure guage, afaik I dont have one.

I havent checked the actual numbers during this bout, yet. I get pretty scattered time to work on this, hence the apparent gap here.
MarkS DEC 13, 07:47 AM
May be I missed it but did you replace the fuel filter? I had a similar issue with my 86 2.8. Turned out to be a rusted tank. You could replace the fuel filter and it would run OK for a bit then the filter would clog again and the same symptoms would reappear.
CZSeventyFive DEC 14, 09:10 AM
Yah, once before the pump was replaced and once after which I only did to see of it was something like you described. I'm not sure how much you can see by just looking in the filter but checking then out after they didn't seem gunked or anything.

This week I'm gonna try to get a guage again and post some pressure numbers, see what I get.
steve308 DEC 14, 03:30 PM
Sounds like mine a few years back......clogged converter was the issue.
Patrick DEC 14, 04:30 PM

quote
Originally posted by steve308:

Sounds like mine a few years back......clogged converter was the issue.



I agree with that possibility (as I once had the same symptoms/problem)... which is why I'm surprised so much effort has gone into a fuel supply issue when no fuel pressure readings were ever taken.
CZSeventyFive DEC 16, 04:08 PM
I took readings before the fuel pump was replaced. I never wrote them down, but we discerned what we got were bad and so I replaced the pump. This was like a year ago. Except for an experimental fuel filter I was looking more at electronics like the sensors and cables (and really I suppose the alternator wasn't worth mentioning as that was a different issue entirely). I probably haven't presented a very good timeline here.

[This message has been edited by CZSeventyFive (edited 12-16-2021).]

Patrick DEC 16, 05:18 PM

quote
Originally posted by CZSeventyFive:

I took readings before the fuel pump was replaced. I never wrote them down, but we discerned what we got were bad and so I replaced the pump.



I understand, but it's important to rule out the possibility of fuel pressure still not being adequate. I'm not saying that lack of fuel pressure is necessarily the issue here, but it wouldn't be the first time that a brand new fuel pump was faulty... or that perhaps a lower pressure duke fuel pump was installed instead of the one required for a V6.

[This message has been edited by Patrick (edited 12-16-2021).]

buddycraigg DEC 22, 04:49 PM
did you ever replace the fuel filter? It could be flowing enough at lower engine speeds, but clogged enough that it can't keep up with higher speeds.