Misfire, where do i go from here. (Page 6/18)
zkhennings FEB 19, 09:24 PM
Tach filter is on the white wire coming off the gray plug on the ignition coil for the duke. The other wire coming off the same plug is a thick red/pink wire. Both wires go to the C500 connector in the engine bay. The tach filter is a little metal cylinder that cleans up the signal from the coil. Square component that was messed up in your dist I believe is the pickup, so with that malfunctioning your ICM/ECU will not know where the timing actually is.

My wiring info is for an 85 2.5, but imagine they stuck with the same colors on the wires.

[This message has been edited by zkhennings (edited 02-19-2023).]

Patrick FEB 19, 09:36 PM

quote
Originally posted by 82-T/A [At Work]:

... you'll definitely want the newer style, it's significantly better than the older style with the tabs. Later GM-style distributors went with this style of pickup, and is why they switched.



I guess what surprises me is that it appears (but not absolutely confirmed) that the '84 duke only ever came from the factory with the "newer" style distributor, whereas the later made '85-'88 2.8 only ever came from the factory with the "older" style distributor... which as pictured below is still available rebuilt.
Dukesterpro FEB 20, 02:08 AM
Hello everyone,

I was away this weekend, part of the urgency to fix this car was a 400+ mile road trip that I had been planning to take in the Fiero. However, considering the fact that I am having consistent and worrying idle and misfire issues, I decided to do the sensible and mature thing and take the car anyways. I am happy to report that she did very well on her trip with no notable change in performance. As long as I stayed under the half pedal, she cruised at 85mph / 3000 rpm with no issues.

Here's a fun Fiero-themed tidbit from my trip. The instigator is the one on the ground. I haven't put it on a pike quite yet.



Anyways back to the topic at hand. Bouncy tach and mystery distributor. I am lucky to have a good relationship with the previous owner of the car and all of the paperwork for the absolute bare minimum amount of work that had been done on it by a dealer. He did all the other work himself. The distributor I pulled is the one that it was delivered to him with. Right from the factory. The replacement I bought from rock auto is visually identical to the original one. The only difference is that it does not have our red component, it expects you to move it over.. The old distributor is stamped Delco Remy. Patrick, does your distributor have anything wired in a similar location. If it does, maybe we can find out the specifications of what it is, and I can try to create a generic version of it.




Something of note. My car does not have an external silver tach filter can. According to the previous owner, it was never removed. He never did any ignition work to the car in the 40 years he owned it except for spark plugs and spark wires.

What do we think that red piece does? If not a tach filter what? Please refer to the little diagram I made to see how it was wired.

[This message has been edited by Dukesterpro (edited 02-20-2023).]

82-T/A [At Work] FEB 20, 12:24 PM

quote
Originally posted by Patrick:

I guess what surprises me is that it appears (but not absolutely confirmed) that the '84 duke only ever came from the factory with the "newer" style distributor, whereas the later made '85-'88 2.8 only ever came from the factory with the "older" style distributor... which as pictured below is still available rebuilt.





No, that's definitely not the case. I bought a 1984 Fiero 2m4 back in the day (mid 90s) that was 100% all original. I also had a 1985 Fiero 2m4 that I bought at auction that was also all original. I've probably futzed through at least ~100 Fieros in the junkyard, and I can pretty confidently say that all the Fieros that were sold, came with the original style of "pickup" rotor as you posted in that image. The newer one with the triangular points within the ring is definitely the newer style.

But it's worth mentioning that the 84 distributor is just different anyway from the 85+ models. The condensor (to answer dukesterpro) is internally mounted within the distributor in the 1984, where as the 1985+ had it mounted externally (from what I remember). In this case, he should just spend the $114 and get the new / rebuilt distributor that comes with everything already.

More on the 84/85 stuff, things were not so cut and dry in 1985, because many many thousands of 1985 Fieros were using parts from 1984s. The 1985 Fiero that I had was a very early-production 1985, and it still had flat-tappet lifters, and a bunch of other things that were 84-Specific (and the VIN matched)... where as they switched to roller-lifters. There were even some 85 Fieros that came with 84 Fiero harmonic balancers.


EDIT: But back on the distributors... to be perfectly clear... no Fiero ever "came from the factory" with the distributor that has the star of David pattern. They all came with the one that looks like little points sticking up. But the "star of David" design is a NEWER design. As I mentioned, if you really want the older style (originality, concourse restoration?)... you can still find them rebuilt. But almost everyone has gone to the newer style because it's better and less likely to foul.

[This message has been edited by 82-T/A [At Work] (edited 02-20-2023).]

Dukesterpro FEB 20, 01:06 PM
I already bought the new distributor. It didn't have the condenser.

Id have to rewire to use the later style distributor with the plugs on the outside right? Besides, it still doesn't change the fact that apparently this car needs that piece. Im lost as to what you guys think i should do here?
82-T/A [At Work] FEB 20, 01:13 PM

quote
Originally posted by Dukesterpro:

I already bought the new distributor. It didn't have the condenser.

Id have to rewire to use the later style distributor with the plugs on the outside right? Besides, it still doesn't change the fact that apparently this car needs that piece. Im lost as to what you guys think i should do here?




Honestly, it should have come with it, it's an integrated part of that distributor, and the one on rock auto when I looked showed it in there. My guess is someone bought it, "borrowed it" and then returned it, possibly. Either way, Call the Fiero Factory, or the Fiero Store... see if they have the piece that you need. Make sure you tell them you have a 1984... there were a lot of one-off things in 84, and early 1985.


Fiero Factory:
https://thefierofactory.com/

The Fiero Store:
https://www.fierostore.com/
Patrick FEB 20, 11:03 PM

quote
Originally posted by Dukesterpro:

Patrick, does your distributor have anything wired in a similar location. If it does, maybe we can find out the specifications of what it is, and I can try to create a generic version of it.



I've had a busy last couple of days. Hopefully tomorrow I can do some Fiero related stuff. I have two '84 Fieros here that I've owned for 20 years. As far as I know, they both have their original distributors. I'll do some digging and report back.
Dukesterpro FEB 21, 10:10 AM

quote
Originally posted by 82-T/A [At Work]:
Honestly, it should have come with it, it's an integrated part of that distributor, and the one on rock auto when I looked showed it in there. My guess is someone bought it, "borrowed it" and then returned it, possibly. Either way, Call the Fiero Factory, or the Fiero Store... see if they have the piece that you need. Make sure you tell them you have a 1984... there were a lot of one-off things in 84, and early 1985.


Fiero Factory:
https://thefierofactory.com/

The Fiero Store:
https://www.fierostore.com/




Well its not technically apart of the distributor so there is no way someone removed it. Its a piece of the wiring harness that happens to bolt into the distributor. if it wasn't broken it would have been permanently soldered in parallel with the pink and black line coming from the coil.

I will definitely give them a call and see what they have. It seems like this is the only fiero to have this capacitor or resistor or whatever. lol.

I eagerly await your response patrick.

82-T/A [At Work] FEB 21, 10:15 AM

quote
Originally posted by Dukesterpro:
It seems like this is the only fiero to have this capacitor or resistor or whatever. lol.



It is, definitely... 1984, and maybe a run of 85s. But that said, it does not mean it's the only GM car that has them. I would suspect there are other GM cars from say, 1982-1984 that also used that same distributor. I'd guess if you took a look at the 1984 Pontiac Grand Am with the 2.5, you'd probably also see the same distributor in there. GM tended to use all of these things across multiple car lines over the years. Like... the ESC that was used in the 80 Corvette also found its way into the Trans Am, Camaro, and even pickup trucks.

EDIT: I would guess that GM changed this for the 1985 model year because of reliability issues. I'd have to assume that having it mounted inside the distributor caused premature failure.

[This message has been edited by 82-T/A [At Work] (edited 02-21-2023).]

Dukesterpro FEB 21, 05:44 PM
Something interesting happened. I was looking at another Fiero for sale and my 84 was idling, high, 1600 rpms, when I got in and took off. It stumbled a bit for the first time tripped a code. Code 42.

I stopped the car and when to look in the back. Nothing seemed wrong. Still idled strong just high. Code went away after a restart. Oddly enough the engine idled correctly, at regular temp for the first time in a long time for about 30 seconds. I was standing there watching it. When all of a sudden it climbed right back up to 1600 rpm. Like someone lightly stepped on the throttle. No one was in on or near the car. Weird Weird Weird.

Fiero Factory doesnt know what Im talking about regarding that capacitor/resistor and I cant get fiero factory to pick up.