Misfire, where do i go from here. (Page 7/18)
Patrick FEB 21, 09:08 PM

quote
Originally posted by Dukesterpro:

...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.



Not really all that weird, as that's what the IAC valve's job is when commanded to do so. Something is triggering the ECU to give the command. The next time the engine appears to be idling at the correct speed, unplug the harness from the IAC valve and see what happens.

I took some pictures of my 84's distributor (which I'll post this evening), but have nothing conclusive to share at this point.

[This message has been edited by Patrick (edited 02-21-2023).]

Patrick FEB 22, 12:59 AM


That's a photo of my '84 parts car. I have no way of knowing for sure, but I believe this is the original distributor... and it's the "newer" style. I suspect all 84's came with this style distributor.


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

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.

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.



I'm still not convinced. Can you find a single picture online of an '84 duke "older" style distributor? If no Fiero ever "came from the factory" with the newer style distributor, there must be tens of thousands of the older style distributors still out there. Todd, I think your memory is playing tricks on you and it was actually "older" style distributors on 2.8 V6s that you're thinking of.

Dukester... in my image above, it's pretty obvious that this distributor has been tampered with (years ago by me). Where exactly was that unknown component mounted on your original distributor? On the outside of the body?

Online image of a Cardone '84 distributor...

[This message has been edited by Patrick (edited 02-22-2023).]

82-T/A [At Work] FEB 22, 07:48 AM

quote
Originally posted by Patrick:

That's a photo of my '84 parts car. I have no way of knowing for sure, but I believe this is the original distributor... and it's the "newer" style. I suspect all 84's came with this style distributor.

I'm still not convinced. Can you find a single picture online of an '84 duke "older" style distributor? If no Fiero ever "came from the factory" with the newer style distributor, there must be tens of thousands of the older style distributors still out there. Todd, I think your memory is playing tricks on you and it was actually "older" style distributors on 2.8 V6s that you're thinking of.



I love you man, you know that, but respectfully, you would argue about ice with an Eskimo. I'm not sure what the point is, this is the better design, and nearly all the new rebuilt distributors have this style. It's the one he should have and would want to get.


Dukespro, wish I could help, but honestly... you're missing the condenser... which is important for ensuring a clean signal to the ECM for timing. I used to have a 1984 Fiero Service Manual... I may still have it in storage if you feel like waiting that long. You might be able to find it online too... I just did a quick search and couldn't find it in PDF format. But this is it basically: https://www.themotorbooksto...175c90b69bdbe3d83819

It'll literally have the part numbers, exploded diagrams, and everything you will need to diagnose and identify the part that you're missing. The problem is that in 1984, it was basically the only year that Fiero had that configuration specifically like that. As I said though, if you can find a U-Pull-It or LKQ junkyard near you, you might want to check to see if there are other cars from that year... something like 1982-1984, either as a Chevy S-10, Pontiac Grand Am, Oldsmobile (whatever it was), etc... basically, anything with a Duke in it, and I guarantee to you that you'll be able to find the parts you're missing.


EDIT: I literally just ordered an original (reprint) of the service manual for my 1987 from that site. If you can swing it, it's worth the price. There's a lot of experience here on the Fiero List, but nothing beats the original service manual for things like this, especially with a 1984... which is probably my favorite year. I know it may not seem like it, but in 1984, the Fiero had a lot of little nuanced parts that none of the other years had (or were discontinued a few years after). Like the threshold name plates (I think, gone by 86?), or the headrest speakers (gone by 86), the one-year only black buttons (84 only), with several interesting seat combinations. They even had fleece seats, which were totally wild looking, last year of those was 1985. There was also a super-rare mirrored sunroof (not sure whether this was good or bad) in 1984. There were some issues too... but 1984 was truly a unique year. Man... I'm tempted to go buy one now.


Ok, just found part of it, go to page 107 (by looking at the pages, not the actual PDF page number):

https://www.fieroinfo.com/m..._Troubleshooting.pdf


It lists it as a "Radio Noise Capacitor"

When looking at Summit Racing, I see a list of possible options: https://www.summitracing.co...se-filter-capacitors


ALL the GM-style ones seem to be special order. I don't really see anything listed for L4/151, but it could just be because they don't seem to care enough to even bother to list it (I've seen this before).

[This message has been edited by 82-T/A [At Work] (edited 02-22-2023).]

Dukesterpro FEB 22, 09:13 AM
First I want to thank 87 and patrick. You guys have been wonderful.

87 that book is going to be a tremendous help. That's really what I was looking for, and being new to this, I had no idea that existed. The big thing was identifying the name and part number. Which you did. I knew it wasnt exactly a condensor, due to it being fed on the solid 12 volt line. It had to be some sort of filter. I think that will help me get started.
Patrick, the part I am looking for it on bolted to the distributor, inside the housing, and wired in parallel to the purple and black wire going to the + pin on the 3 pin side of the ICM. Best thing that could be done is if you could carefully remove it by clipping the wire and measuring the capacitance of the filter so i match up an identical one from 87s provided material

[This message has been edited by Dukesterpro (edited 02-22-2023).]

Dukesterpro FEB 22, 09:18 AM
Ok after some research this is not my problem. All this capacitor does is filter noise out of the charging system to prevent feedback to the radio. Its not required to have the car run right if your radio has noise reduction built into it. (I have a touchscreen radio with all that jazz already built in) later Fieros apparently didn't have these filters when they went to the more modern pushbutton style radio. Damn

I'm back at square one. However, 87s reference material claims I should have a tach filter. Which I thought I didnt. I might need to go back and look harder.
82-T/A [At Work] FEB 22, 10:28 AM

quote
Originally posted by Dukesterpro:

Ok after some research this is not my problem. All this capacitor does is filter noise out of the charging system to prevent feedback to the radio. Its not required to have the car run right if your radio has noise reduction built into it. (I have a touchscreen radio with all that jazz already built in) later Fieros apparently didn't have these filters when they went to the more modern pushbutton style radio. Damn

I'm back at square one. However, 87s reference material claims I should have a tach filter. Which I thought I didnt. I might need to go back and look harder.




To be clear, the filter definitely ALSO does that, but it can also have an effect on the performance of the engine due to interference with the ECM. I'm not looking at the chart in front of me, but without that radio noise suppression filter, it's not grounding out a wire that otherwise should be ground. Again, I'm not looking at it, but that piece that comes out of the distributor has two leads going to it. One grounds out, and the other continues on, does it not? With it missing, are there not connections which are not being completed?

You do also want a tach filter, without one, the ECM may not be getting a good signal to adjust timing.
Dukesterpro FEB 22, 11:36 AM
That filter grounds out right there. From 12v purple and black to the distributor housing. 2 leads.


Im wondering if my tach filter is there and I just dont see it. Its starting to bug me that I know this harness has not been modified and yet I dont see a tach filter or evidence of one at all.

[This message has been edited by Dukesterpro (edited 02-22-2023).]

ArthurPeale FEB 22, 11:54 AM
I think that's a capacitor?

[This message has been edited by ArthurPeale (edited 02-22-2023).]

82-T/A [At Work] FEB 22, 12:15 PM

quote
Originally posted by Dukesterpro:

That filter grounds out right there. From 12v purple and black to the distributor housing. 2 leads.

Im wondering if my tach filter is there and I just dont see it. Its starting to bug me that I know this harness has not been modified and yet I dont see a tach filter or evidence of one at all.




Yes, ok... that's what I thought. So if I'm not mistaken, not having that plugged in or attached properly (or a failed one), is likely leading to a circuit not being completed. When you say purple and black, you mean black and purple as the 2 leads? I don't know what it does, but it's possible that maybe those two connect somehow within the radio noise suppression filter. So without it... it's not making that connection. You definitely want this.

Yeah, and there should be a tach filter... maybe it's serving as both? I don't know... it's kind of the same thing.
Dukesterpro FEB 22, 12:45 PM
Its a black wire with a purple stripe. Its sole purpose is to provide 12 volts from the coils 12 volt supply the ICM.

My nearly completed CET degree is making me think that this is simply a form of back-emf protection so you don't hear whining over the radio from the ICM's micros working.

This capacitor doesn't appear to make any connection, since its run in parallel to the plug. All that happens is you have a bit more noise in the electrical system. Further, when I plugged my old radio back in, it makes a whining noise it never used to. I did find a replacement capacitor just in an electrolytic flavor instead of ceramic. Its on the way so I guess I am going to have to put up or shut up.

Can't wait to do a bunch of more work and find out you were right all along. lol.

I ordered a scanner from OBDDiagnostics today. Its time to get serious. In the mean time, I'm am going to try to locate that tach filter. It has to be there, because the tach worked really really well when I first got the car.

I will keep everyone posted. Please keep feeding me ideas and information if you think of anything. This is been very informative and I feel that all these ideas, even if they weren't my solution may be a valuable resource to others in the future. Especially as the popularity of the 84 seems to be on a uptick. At least in my area.