Misfire, where do i go from here. (Page 10/18)
Patrick FEB 24, 04:28 PM

quote
Originally posted by Dukesterpro:

Do remember this is one of the safest non airbag cars ever built. Stronger than strong subframe.



When the Fiero came out, it was rated #2 in crash tests. Only Volvo beat it out of top spot. There's a reason why the doors on a Fiero are so freakin' heavy!


quote
Originally posted by Dukesterpro:

My dad taught me to drive like everyone is out to get me. He mercilessly beat that notion into my head to stay away from everyone. Saved my bacon more times than I can count now.



Over the last half-century that I've been driving (and half of that with one Fiero or another), the only assumption I ever make about anything is that other drivers can't see me. I don't know how many times when entering an intersection (where I have the right of way) that I've seen the other driver look right at me... and then pull out into my path! Always be prepared for hard braking and/or evasive measures.

[This message has been edited by Patrick (edited 03-21-2023).]

maryjane FEB 24, 08:20 PM

quote
Originally posted by 82-T/A [At Work]:
This is very suspect. Can someone verify for me here if this is correct or not?

My V6 Fiero typically runs 42 PSI, and ~38 when running.

13-PSI to me seems extremely low, but to be honest, I never remember checking fuel pressure of my 4 cyl Fieros when I've owned them. I know that 4-8 PSI is pretty normal for a carbureted application (with like, a pusher pump), but 13 PSI just seems a little low. Now that I think about it, I don't even remember where to measure fuel pressure on the 4 cyl since there isn't a fuel rail (just a TBI). How are you measuring that fuel pressure?
13 PSI might be normal, I know it's not for a V6.... but that could be your issue.

I also know that sometimes the tube that goes between the fuel pump and the pickup can get crushed and collapse if it's not replaced when you replace the fuel pump.




13 pi is correct for the 84. Pressure regulator is built in at throttle body.
Saw where you replaced fuel pump 9 months ago. Pressure and flow are inexorably related, with more flow required upon acceleration. Did you check pressure using the procedure outlined to squeeze off the r eturn line slightly?
I had an '84, that would start and run fine at idle, even under light throttle, but bogged down and bucked upon throttle demand, such as getting up on an on ramp. It would eventually get up to speed but test showed 9psi fuel pressure..

To test FP on an 84 duke, you can either rent a test kit from AZ or another parts store and hope their adapters mate up to your decades old engine or do what I did and just make your own out of stuff I had around anyway. (<20psi ain't no high pressure gig anyway)


I did not read thru all the posts, but I did see the picture of the mystery device. The tach filter on all of my 84s was in the wiring harness away from the distributor bit.
Kinda taped up in the wiring bundle near the thermostat housing and left of the coil.

[This message has been edited by maryjane (edited 02-24-2023).]

Patrick FEB 24, 09:09 PM

quote
Originally posted by maryjane:

The tach filter on all of my 84s was in the wiring harness away from the distributor bit.
Kinda taped up in the wiring bundle near the thermostat housing and left of the coil.



I'm going to have to take a closer look at the two 84's I have here!


quote
Originally posted by maryjane:

I did not read thru all the posts, but I did see the picture of the mystery device.



Well, come on Don... it's the "mystery device" we want to know more about! lol

[This message has been edited by Patrick (edited 02-24-2023).]

Dukesterpro FEB 25, 12:32 AM

quote
Originally posted by maryjane:
13 pi is correct for the 84. Pressure regulator is built in at throttle body.
Saw where you replaced fuel pump 9 months ago. Pressure and flow are inexorably related, with more flow required upon acceleration. Did you check pressure using the procedure outlined to squeeze off the r eturn line slightly?
I had an '84, that would start and run fine at idle, even under light throttle, but bogged down and bucked upon throttle demand, such as getting up on an on ramp. It would eventually get up to speed but test showed 9psi fuel pressure..

To test FP on an 84 duke, you can either rent a test kit from AZ or another parts store and hope their adapters mate up to your decades old engine or do what I did and just make your own out of stuff I had around anyway. (<20psi ain't no high pressure gig anyway)


I did not read thru all the posts, but I did see the picture of the mystery device. The tach filter on all of my 84s was in the wiring harness away from the distributor bit.
Kinda taped up in the wiring bundle near the thermostat housing and left of the coil.






Well, I'll be dipped. I didn't even think to look that far back for the tach filter. I will check it out in the morning.

I was not aware of the whole pressure test routine. I just hook a pressure gauge inline after the fuel filter and revved the engine up to 4500. Held pretty stable at 13.

Im gonna go deeper into the harness, everyone said it was bolted to the engine right near the distributor so I didn't think to go that far back. Maybe we are on to something.

Thank you for the information MaryJane.


I did identify that mystery part a few posts back, it's a radio filter. According to some GM documentation, it is there for cars with older non-pushbutton radios that don't have a filter built into them. Without it, you get a whirring noise in your stereo that revs with the engine. I still want to replace it, but I would like to find someone who has a good one so I can verify its capacitance and source some new ones from digikey. You can guess and over shoot its capacitance but you loose filtering efficiency the more off it is. Too little capacitance and pop go the weasel.


Thanks again everyone, we have to be drawing near a breakthrough
Patrick FEB 25, 01:05 AM

quote
Originally posted by Dukesterpro:

I did identify that mystery part a few posts back, it's a radio filter. According to some GM documentation, it is there for cars with older non-pushbutton radios that don't have a filter built into them. Without it, you get a whirring noise in your stereo that revs with the engine. I still want to replace it...



Well damn, I don't know why we're worrying about it then. I thought there was perhaps still some belief that maybe it was required for "optimum" performance of the ECU.
maryjane FEB 25, 01:52 AM

quote
Originally posted by Patrick:

Well damn, I don't know why we're worrying about it then. I thought there was perhaps still some belief that maybe it was required for "optimum" performance of the ECU.



Since you and Todd went off in the weeds about the distributor, I'm gonna throw a wrench in the works.............



I understand it's there for a purpose, (RF suppression) but don't understand what it's doing in this particular harness....... It's gonna make you go
Patrick FEB 25, 02:11 AM

Wow, where'd you dig that image up from?
maryjane FEB 25, 03:10 AM

quote
Originally posted by Dukesterpro:

I did identify that mystery part a few posts back, it's a radio filter. According to some GM documentation, it is there for cars with older non-pushbutton radios that don't have a filter built into them. Without it, you get a whirring noise in your stereo that revs with the engine. I still want to replace it, but I would like to find someone who has a good one so I can verify its capacitance and source some new ones from digikey. You can guess and over shoot its capacitance but you loose filtering efficiency the more off it is. Too little capacitance and pop go the weasel.


Thanks again everyone, we have to be drawing near a breakthrough



I'm pretty familiar with the "whirring noise" from ignitions (and from charging systems). Cut my mechanical teeth on Flat heads with 6 and 8 volt systems using a generator that weighed nearly 30 lbs. Anything with points will drive you crazy on a long trip if not 'RF' suppressed. Early electric wipers also caused the same noise, especially on the old AM radios.


maryjane FEB 25, 03:18 AM

quote
Originally posted by Patrick:


Wow, where'd you dig that image up from?


Remember, Fieros were at least partly built from "off the shelf" parts to save $$$.
They used that same RF capacitor as other vehicles before and after the 84.
The one in the picture, is in a wiring harness for the AC Delco D1515B Twilight Sentinel Headlight Switch For 1985-1990 Olds 98

That isn't nearly the only application or year that GM used that same device,but, no Olds 98 for those years came with the Mighty Duke.
(You can buy that one off ebay for $138.88)

https://www.ebay.com/itm/185205560638

[This message has been edited by maryjane (edited 02-25-2023).]

Patrick FEB 25, 04:17 AM

quote
Originally posted by maryjane:

The one in the picture, is in a wiring harness for the AC Delco D1515B Twilight Sentinel Headlight Switch For 1985-1990 Olds 98



Maybe I should've asked you how you dug up that image! What led you to that particular Headlight Switch(!) harness which has the same "mystery" capacitor as the one we've been fretting over for the last few days?

[This message has been edited by Patrick (edited 02-25-2023).]