Trouble starting, then very rough idle and backfires (Page 2/4)
sleek fiero FEB 13, 11:25 PM
Check your fuel filter. that plug looks very lean and overheated. sleek
Patrick FEB 14, 12:57 AM

quote
Originally posted by WingsGT:

Image imbed didn't work...





The Upload Media tab works fine. Just make sure you're logged in before trying to post.

Many people here will disagree with your choice of plugs. Supposedly they don't work well with the 2.8's factory ignition system. The advice often given is to use standard ACDelco (or NGK) plugs, and not those highfalutin ones with tiny electrodes.
WingsGT FEB 14, 05:50 AM
Thanks Patrick. I had tried the image tags added with the button up top but alright, upload media next time.

I got these NGK before I knew much about the car and I had used them on previous vehicles. But from what I've read I'm convinced to get ACDelco next time. These seem like they might be okay for a little while more?

Could it be lean? I've always suspected the car was running rich. Replaced the fuel filter a while back as well. The one I took off looked pretty clean, maybe replaced not that long ago by the previous owner.
Patrick FEB 14, 06:07 PM

quote
Originally posted by WingsGT:

I got these NGK before I knew much about the car and I had used them on previous vehicles. But from what I've read I'm convinced to get ACDelco next time. These seem like they might be okay for a little while more?



I'm rather surprised that The Ogre (theogre) hasn't chimed in on this, but he's quite adamant that those plugs you're using will cause problems when installed in a Fiero 2.8 engine. I've never used them myself in a Fiero, so I can't confirm nor deny what he says about them.
1985 Fiero GT FEB 15, 04:49 PM

quote
Originally posted by WingsGT:


Checked TPS, I've got 0.35V closed and 4.56V at open throttle.



Going off of memory, isn't the TPS supposed to be 0.2v closed about 5v open, the open doesn't seem to bad, maybe a little low, but .35v closed on mine was enough to cause done of the problems you describe, I got check engine light, and throttle response was horrible, if I gave it gas to quickly, then it would seem to backfire a bit out the intake, and smelled bad. If I drove it, I'm sure mpgs would have been bad, it had a high, unstable idle, and was really easy to stall.
jelly2m8 FEB 16, 02:21 AM
Backfiring is an Ignition or valve timing issue.

Throw those plugs straight into the garbage and put standard Copper plugs in it, AC Delco preferable and start there.

Put a socket/ breaker bar on the harmonic balancer bolt and turn it back and forth and see how much free resistance (slop) there is before you feel the drag of the Camshaft / drivetrain. There should be very very little slop, anything more than just a hair you may have a worn timing chain and possible it jumped camshaft / valvetrain timing.

Fiero Pickup coils and ICM's generally either work or don't, but who knows.

Forget the TPS, The 2.8 injects fuel above the intake Valve where it pools ( when I say pools, I don't mean liquid gas, I mean the fuel/ air charge is there ready to go it} even under normal condition and does not get introduced to any combustion process until that intake valve opens. Ultimately The intake valve opening controls when the charge is is injected into the combustion chamber.


If it is backfiring continually as it's running, possibly it could be a burnt valve, that Spark plug pic does have a nasty gray color to it.

[This message has been edited by jelly2m8 (edited 02-16-2024).]

WingsGT FEB 16, 03:04 PM

quote
Originally posted by jelly2m8:

Backfiring is an Ignition or valve timing issue.

Throw those plugs straight into the garbage and put standard Copper plugs in it, AC Delco preferable and start there.

Put a socket/ breaker bar on the harmonic balancer bolt and turn it back and forth and see how much free resistance (slop) there is before you feel the drag of the Camshaft / drivetrain. There should be very very little slop, anything more than just a hair you may have a worn timing chain and possible it jumped camshaft / valvetrain timing.







This distance is 4 degrees right? Is that too much?
jelly2m8 FEB 18, 05:55 PM
That is quite a bit of slop, and that's not even without any load on that timing chain in which it probably stretches more.

A quick test would be to add a few degrees of ignition timing and see if that makes any difference in starting and or roughness. This isn't a fix but may help diagnose or confirm a timing issue.

Higher mile 2.8's always ran better with 12 degrees ignition timing just for this reason.

[This message has been edited by jelly2m8 (edited 02-18-2024).]

Patrick FEB 18, 06:31 PM

quote
Originally posted by WingsGT:

This literally happened overnight...



I think it's pretty safe to say the timing chain didn't stretch overnight.

I'm not suggesting there isn't any slop there, but I doubt that's the cause of your current issue.

Got WinALDL up and running yet?

Have you at least tried some regular spark plugs?
WingsGT FEB 18, 09:04 PM
I just found the ALDL connector I bought a while ago but never finished looking into WinALDL. Getting a little busier this week but I should be able to get that going in the next few days, and in the mean time I will be ordering the correct spark plugs. The instructions for the cable show it wired to a DB9 connector for RS-232 serial. I have an RS-232 to USB adapter and I saw some posts saying that should work, but is there anything tricky I might need to know to get it working right? If it's as simple as it looks that would be awesome but just in case you have any tips!

But I am worried about running it long enough to get a live readout or change timing. I know at some point I might have to start taking riskier troubleshooting steps, I just want to make sure it's as safe as possible. Maybe I should do a full compression test, but also if it's backfiring it seems like that might be conclusive enough that it would fail somewhere. Could I find valve damage from "just" taking the covers off? I've read that it's difficult with everything assembled. Some people saying they did it with the intake on and others saying they had to take the whole thing off, or just the upper plenum. I'm not super confident about maneuvering wrenches back there without clearing some space since I haven't done it before, and just changing the even number spark plugs is hard enough. Also not excited about trying to hook up the compression tester to those cylinders either but at some point I've got to get over that. If I was digging into it to check stuff, I would like to replace the fuel injectors and regulator while I'm there but I also don't want to introduce new problems while trying to find this one.

Engine has about 87,000 miles afaik. When I bought it the speed sensor was going out intermittently and then totally failed on the drive home. Amazing how that happens.

Would it be unreasonable to take the cylinder heads off and have them rebuilt, and replace the timing chain myself at this point? It doesn't seem like it would be a crazy amount of money since I found a place that said they could rebuild heads for $100 each, which I found kind of surprising considering other quotes I got in this area but I think they're legit. I really want to keep the cylinder heads in good condition for a 3.4L swap down the road. I've been trying to learn stuff gradually in the hopes I would be able to handle that swap comfortably by the time something major failed on the 2.8, but now here we are.