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85 GT Struggling for/Losing Power or Throttle not engaging? by CZSeventyFive
Started on: 12-12-2021 09:32 PM
Replies: 15 (219 views)
Last post by: CZSeventyFive on 01-14-2022 11:40 AM
CZSeventyFive
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Report this Post12-12-2021 09:32 PM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
'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?
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Patrick
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Report this Post12-12-2021 10:03 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
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).]

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CZSeventyFive
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Report this Post12-13-2021 05:40 AM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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MarkS
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Report this Post12-13-2021 07:47 AM Click Here to See the Profile for MarkSClick Here to Email MarkSSend a Private Message to MarkSEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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CZSeventyFive
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Report this Post12-14-2021 09:10 AM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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steve308
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Report this Post12-14-2021 03:30 PM Click Here to See the Profile for steve308Send a Private Message to steve308Edit/Delete MessageReply w/QuoteDirect Link to This Post
Sounds like mine a few years back......clogged converter was the issue.
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Patrick
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Report this Post12-14-2021 04:30 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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.
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CZSeventyFive
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Report this Post12-16-2021 04:08 PM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
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).]

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Patrick
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Report this Post12-16-2021 05:18 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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).]

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buddycraigg
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Report this Post12-22-2021 04:49 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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CZSeventyFive
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Report this Post01-07-2022 03:27 PM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
Got a guage to check the pressure at idle, at about 31. Not sure how much can be told at idle, revving it didnt change it really.

Its parked in a garage at the bottom.of a snowy, I'll plowed hill so I dont think I'll have much luck getting it up until some of it goes away. So I have this to start. I'll try to attach a picture to this post.
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Patrick
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Report this Post01-07-2022 03:49 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by CZSeventyFive:

Got a guage to check the pressure at idle, at about 31.


Unfortunately, that's below specs. What is an acceptable fuel pressure "range" for the V6? Should be 35-40.

How quickly does the fuel pressure drop when the engine is turned off?
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Skybax
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Report this Post01-07-2022 06:49 PM Click Here to See the Profile for SkybaxSend a Private Message to SkybaxEdit/Delete MessageReply w/QuoteDirect Link to This Post
Since your focus has been mainly on fuel delivery, nobody has mentioned ignition... I would suggest putting a new coil on it because its easy and cheap, a bad coil will often do what you describe (run but engine falls on its face when put under load). A good quality replacement coil is a Standard Blue Streak and they cost about $30, if it turns out to not be the coil, then you can keep your good old coil in the trunk as a backup. (note: be gentle with the connectors and wires going to the coil and make sure they are fully seated)
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CZSeventyFive
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Report this Post01-08-2022 12:42 AM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Patrick:

How quickly does the fuel pressure drop when the engine is turned off?


I would have described it as moderate to moderately quickly IIRC. If it's low at idle then I suppose driving it would have also been rather out of spec. Though I should still get those numbers too, when possible.

 
quote
Originally posted by Skybax:

Since your focus has been mainly on fuel delivery, nobody has mentioned ignition... I would suggest putting a new coil on it because its easy and cheap, a bad coil will often do what you describe (run but engine falls on its face when put under load). A good quality replacement coil is a Standard Blue Streak and they cost about $30, if it turns out to not be the coil, then you can keep your good old coil in the trunk as a backup. (note: be gentle with the connectors and wires going to the coil and make sure they are fully seated)


I'll look into it. A while back there was a point where when trying to start it the car it would turn for a couple seconds before going, but then that just stopped one day and hasn't occurred since.
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Patrick
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Report this Post01-08-2022 01:01 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by CZSeventyFive:

I would have described it as moderate to moderately quickly IIRC.


The pressure should hold steady for at least several minutes before dissipating. I suspect you've either got a leak within the tank (the flexible hose connection to the pump) or one or more of your fuel injectors are leaking.

I suppose it's also possible that the fuel pressure regulator diaphragm could be leaking. I haven't had experience with that myself, but I do recall reading here in the past how to check for that.

[This message has been edited by Patrick (edited 01-08-2022).]

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CZSeventyFive
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Report this Post01-14-2022 11:40 AM Click Here to See the Profile for CZSeventyFiveSend a Private Message to CZSeventyFiveEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Patrick:but I do recall reading here in the past how to check for that.



Maybe this thread? I'm reading through it and seems to be detailing a similar issue, plus what appear to be some testing methods. I suppose I'll try some of these. I will admit when I replaced the FPR shortly after I bought the car (on the suggestion of the previous owner, who thought it was causing a high idle, though in reality I think the idle was just due to bad gaskets) there was a troubled installation, likely due to my own inexperience (first car I've tried to really "work on," per say).

Namely, when taking the old one out one of the small torx screws stripped/broke, and I ended up drilling out the remains and widening the hole in the rail to accommodate a slightly larger screw (we didn't think we had much of a choice given how it was). Then I installed the parts in the wrong order (the circle plate went under the top hat shaped cap instead of over it, which of course is to hold it down. Pretty moronic, yes I know). I realized it pretty quickly and went back in to put the parts right, but I've since wondered if something else got damaged as a result or if the regulator simply hasn't worked since then (though again, I find it weird that it drove fairly effortlessly after a pump installation, but who knows). So really I may have broke it pretty early.

But I'll follow this thread I linked a bit and see what comes of it, if anything.
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