Hunting Gremlins and Misfires in my 86 Fiero GT (Page 1/2)
bootdsc JUN 09, 05:47 AM
*edit* Solved, the main problem was a failing pulsator, replaced with fuel submersible 5/16th hose and high pressure clamps.

I've learned a lot about this 86 fiero gt (automatic) in the last week of wrenching on her but these gremlins have me feeling like a noob.

The car was running on default/limp when purchased which i was unaware of or i would have drove the price down another grand, i have started to replace everything for the sake of having a nice tuned up reliable daily driver but also because of the chity chity bang bang spudder misfire it developed.

May be important to mention it was only 75-80 when i bought the car and has been 100-110 for a few days before the problems started.

First up replaced the O2 sensor that had broke in half and blown out the side of the manifold. Also while in the engine bay i reconnected the vapor canister. This took care of the code 13 and 44.

Few days later the temp gauge was a bit jumpy and when i parked to pickup groceries it overheated and spewed out coolant, there was a great deal of air in the system, i refiled it the correct way and no more heat issues and no air bubbling into the reserve tank.
Car ran fine for the next couple of days.

Now on another real hot day the engines running good for about 30 minutes until it starts misfiring, sputtering, idle jumping. My first guess was something overheating again so i let it cool down than limped it home, it ran ok but didn't have much power until getting up to speed and over 2500rpm it ran fine.

Started looking into what might be the cause and down the rabbit hole we go.
Everything i have done so far has not just been in the hopes of fixing this misfire but also for general maintenance and tune up. These were all done one at a time with some driving in between and ecm resets to see if there was any improvement.

I have replaced all of the soft vacuum lines and the hard lines look to be in good shape but next up ill do the spray test, i haven't bothered yet since the motor would just stall when turned on and left in park so its hard to check for rpm jumping when it wouldn't even stay on. i decided to move on with replacing stuff until it ran a little better.

Cleaned and reinstalled engine to body ground strap connections, installed second ground strap. This fixed the flickering and dim dashboard lights but had no other noticeable affect.
Replaced the air intake filter. I've never seen such an old and filthy filter on a car.

Spark plugs showed normal wear and no abnormal corrosion or build up but had signs of arcing over the ceramic.

Replaced with stock ac delco.
New spark plug wires from Napa, premium lifetime warranty set. idk who makes them.
New ac delco ignition coil.
Remanufactured distributor from napa, came with rotor, cap and icm. The original was rusted and corroded plus the coil pickup was falling apart so bad idk how the car even ran.

Did the timing the best i could, its like 10.25-10.50. This was difficult with the unstable idle but the engine did settle down after some time.

I'll revisit this as i think it might be making it run lean?
Replaced the starter motor, the repeated cranking while working on the car(mostly from doing the timing) smoked the old one pretty good.

It had that wonderful burnt coil coating smell and was starting to load the battery real hard with every start which was taking longer and longer, i even had to start jumping the battery.

Replaced PCV, old one still seems to be in working order but it had a lot of gunk built up.

Replaced the air charge temp sensor. I don't know if the old one was bad but it was covered in a thick layer of rust.

Replaced IAC and here's where i actually thought i had figured out the cause of my misery.

I unplugged the old IAC and like magic there was no more weak idle, no misfire and the engine wasn't dying while stopped in drive. RPM stayed at 1300 while stopped and would shoot up to 2500 while in park, if i turned the AC on while parked it would settle around 1500.

The car had all its power back and everything seemed great. the next day it was back to the misfire, spudder, idle dropping and not being able to accelerate or even get the rpm's over 3k.

Replaced the IAC (no ecm reset) and after a few minutes of driving got a engine light, stopped and checked it was 35 and 44. Reset the ecm and started trying to drive the car around to let it relearn everything but it was back to having little power and wanting to dye with low rpm every time i slowed down.

Eventually it started running decent so i took it for a long drive and it seemed like the ecm relearned its stuff and was driving pretty good.
Took it up on the freeway and within a few minutes loss nearly all power and had to stop. I unplugged the new IAC and like magic again there was almost no studder, only 1 misfire and no low idle problem.

This brings me to right now where i'm running out of ideas. I don't have a known good ecm to try out nor do i want to buy one and wait 10 days for delivery. The MAP sensor may need replacing but i wont bother until after i can properly test the vacuum lines and today i found my vacuum pump gauge is dead, probably a bad internal seal.

One other thing that idk if its useful info but besides running on limp when i bought it the fuel pump relay was bad and the car was driving with the oil pressure switch engaging the pump. I replaced the relay and now the pump turns on like it should.

What i can't figure is why it'll run fine all day than suddenly start the misfires one day but another it'll be right when it starts up, its all very random. It does seem like i've been dealing with multiple problems. Grounding is fixed, 02 sensor fixed, ICM grounding bolt fixed, weak spark fixed, fuel pump relay fixed.

In between this intermittent problem the motor runs great, the cars so ****ing fast and fun to drive, i can quickly accelerate up a steep incline without issue. I've got the rear sway bar kit sitting in the living room waiting to be installed.

This is one sweet ride and i've just got to figure out this last problem it has. The fiero forum isn't terribly useful since most posts are over 10 years old and few people ever bother to post the solution or maybe they just gave up? Idk but if any of you have bothered to read this whole thing and have a solution that fixes my engine ill buy you a six pack.

I'll be reposting this in all the fiero forums and maybe some other reddit subs so maybe it'll be seen by someone who knows.

[This message has been edited by bootdsc (edited 06-21-2020).]

Gall757 JUN 09, 08:30 AM
You may want to break that post up into a few paragraphs that more of us can tackle at our own pace. Its easy to get lost in all that text..
fierofool JUN 09, 10:51 AM
I have the same misfire problem. Sometimes it does. Sometimes it doesn't. Watching
theogre JUN 09, 11:14 AM
pull tack filter when trying to fix problem(s) w/ HEI.
See my Cave, HE Ignition and Ground "Myth" notes

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

fierofool JUN 09, 01:13 PM
I couldn't get those two links to open. Computer just clocked on both.
Patrick JUN 09, 02:35 PM

quote
Originally posted by Gall757:

You may want to break that post up into a few paragraphs that more of us can tackle at our own pace. Its easy to get lost in all that text..



Agree 100%. No disrespect to the OP, but I don't even bother to try and read something that long with no paragraphs to facilitate easier reading. Just go back and edit your post by using the Enter key a bunch of times!


quote
Originally posted by fierofool:

I couldn't get those two links to open. Computer just clocked on both.



I have the same problem when trying to access the Ogre's Cave. First noticed it a couple of days ago.

[This message has been edited by Patrick (edited 06-09-2020).]

Notorio JUN 13, 12:59 PM

quote
Originally posted by Patrick:

I have the same problem when trying to access the Ogre's Cave. First noticed it a couple of days ago.




Try again today (13th). The Cave links worked for me this morning.
Notorio JUN 13, 01:05 PM

quote
Originally posted by bootdsc:
In between this intermittent problem the motor runs great, the cars so ****ing fast and fun to drive, i can quickly accelerate up a steep incline without issue ...



It's safe to say that even the v6 version is rarely described as 'fast'. Something to keep in mind is that a previous owner may have done some upgrades that you are not aware of, not that that helps in the present circumstances. Now that the links are working check Ogre's Cave. My thought was perhaps the EGR is misbehaving.
Patrick JUN 13, 05:01 PM

quote
Originally posted by Notorio:

Try again today (13th). The Cave links worked for me this morning.



The various links to Ogre's Cave now seem to eventually work, but they each take about ten seconds to open... which in this day and age of instant internet access, is an eternity!
bootdsc JUN 15, 05:16 AM
Blame the formatting on copy paste, fixed it well enough.
I'll have a look at that ground reference wire thanks. The cave has already been a big help in figuring out everything.

Okay so there has been some progress made.

EGR tube was snapped clean in two and certainly the main problem I've been having. Made a temporary fix using a combination of jb weld exhaust pipe repair kits. I'll get a new one from fierostore.

The battery I bought from autozone wasn't rated for high enough cranking amps, my fault for not checking and going off what their system recommended. Swapped it out and I'm able to start it reliably on the second try.

There's still some idle hunting and misfires but I'm pretty sure it's just another small vacuum leak from a rubber block that connects 4 vacuum lines, it's right by the thermostat housing. I haven't found a suitable replacement so I'm just going to build one.

Tomorrow I'll replace the map and water temp sensor, that'll only leave the oil pressure sensor to replace later down the road.

There's one last thing I haven't found a answer to, there's 1 random black wire that's broken off of something in the same area of the map sensor and I just can't find where it goes. I'll post up a picture later, maybe one of you fine sirs will know.

The previous owner kept good records and they did more maintenance than I'd expect from anyone but the car was garaged for 2 years and it hasn't had anything replaced in the last 8 years, don't know how much of that time it spent on the road.

She seems to be in good shape overall, besides the not so fun part of fixing random **** I'm getting ready to build some 2" fender flair's in the rear and 1" in the front, I hate calling it a widebody mod. It's going to be painted hugger orange and I'll leave the silver trim stock.

Any good reason to not use wheel spacers with the Fiero? I really like the stock wheels and I don't want to replace them just to get the offset I need

[This message has been edited by bootdsc (edited 06-15-2020).]