With apologies to Dukester for this slightly off-topic divergence, I think I've resolved the disagreement between 82-T/A [At Work] and myself.
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Originally posted by 82-T/A [At Work]:
...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.
Sorry Todd, but it turns out you are absolutely wrong. According to information I've dug up, '84 dukes indeed "came from the factory" with the "newer" style distributor... which is what I've suspected all along.
I had to use the Wayback Machine, but I found a site Here with some pertinent information on Fieros. He apparently had an '85 duke. In his distributor rebuild section Here, the fella says something pretty interesting!
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I’d replaced my old distributor with one of a better design. I’d thought that was a ‘new and improved’ design, but it turns out that it was the design that was used in ’84, which was replaced the next year with a cheaper, flimsier design. No wonder GM went with a distributorless ignition in ’87.
When I read that, I was inspired to do an online search for an '85 2.5 distributor, and bingo... the "older" style duke distributor.
So... what's it all mean? It means that '84 Fieros came from the factory with the "newer" style distributor. The '85-'86 dukes then came from the factory with the "older" style (probably because they were cheaper to make)... but because they were also flimsier/inferior, many (but not all) replacement distributors for the '85-'86 duke incorporated the superior aspects of the '84 distributor. (They're not exactly the same distributors.)
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Originally posted by 82-T/A [At Work]:
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...
Todd, the "point" was that I wanted the truth of the matter to come out. Now that it has, we can find something else to disagree on.
[This message has been edited by Patrick (edited 02-24-2023).]
But without knowing its actual uF and V ratings...
I had earlier linked to a site Here that discussed Fiero tach filters. At that site was a link to a schematic.
Keep in mind that it's a schematic of a tach filter for a 2.8 V6... but would one for the duke necessarily be any different?
[EDIT] The more I dig, the more I'm finding out. Here's something interesting from Rodney Dickman's tach filter page...
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A direct replacement on ALL years of the 2.8 V6 and the 84-86 2.5 L4 Fiero motor.
Looks like you can just wire one of Rodney's tach filters in and you're all set! If in doubt, contact Rodney and explain the situation. He's a knowledgeable guy.
[This message has been edited by Patrick (edited 02-24-2023).]
I don't mind the off topic divergences at all. Its good information and now its there for everyone to have.
While that's good information to build a tach filter. 82-T/A's documentation shows that my assumption this was related to the tach was wrong. The tach filter is on the white wire after the ICM. This doodad is on the 12V purple and black wire before the ICM. I might just give it the ole leroy jenkins treatment and throw something on there to see if it helps. Start at 47uF and go from there.
With apologies to Dukester for this slightly off-topic divergence, I think I've resolved the disagreement between 82-T/A [At Work] and myself.
Todd, the "point" was that I wanted the truth of the matter to come out. Now that it has, we can find something else to disagree on.
I don't think this is the silver bullet you think it is... but I will admit when I'm wrong, and you've converted me. I believe you, and I apologize! Hahah... damn you!
I would like some additional information on this, because I really want to correct my webpage with some better information. I do think the "new and improved" one that we now think came with the 84 is still a better design, and I'd like to emphasize that. But just want to be clear on it.
After all this pain and suffering, I still would recommend this car.
Its never run perfectly, but it always runs.
Its never not delivered me to work, nor failed to shuttle me home.
As long you and her have the patience to deal with these quirks. Go for it. She will never forget it.
Just teach her good defensive driving. Stay away from everyone always.
As an added bonus the iron dukes guarantees[i] that she will never get a speeding ticket.
**** **** **** !!!
I just bought another Fiero... damnit... haha... what the hell is wrong with me.
Here it is in all its glory... now I need to bring cash and make the 3 hour trip...
I'm such an idiot... lol. I literally already have a Fiero that's not running.
But truth be told, this is for my daughter. I swear, when I told my wife this, I was not making it up. I had this car up on the screen, feverishly looking up distributors so I could prove Patrick wrong (just kidding), and I had it on the screen. My daughter came in and was like... Ooooh!!! I like that car, and then commented on the pop-up headlights, and how she liked that it was small. So I told her... would you like this for your first car? You'll have to earn it, but we can work on it together... and of course she said yes.
So I put in a low-ball offer of $4,000... but told the owner that I'd had many Fieros in the past. And he accepted while thinking about it overnight.
What a lovely little ride 82-T/A! I'm sure you daughter is going to love it. Lots of a good bonding to be had over these funny little buggers.
Always make sure to stress defensive driving. When you are in one of these cars, every thing else on the road is the enemy. Its better arrive alive driving like a grandma away from everyone.
What a lovely little ride 82-T/A! I'm sure you daughter is going to love it. Lots of a good bonding to be had over these funny little buggers.
Always make sure to stress defensive driving. When you are in one of these cars, every thing else on the road is the enemy. Its better arrive alive driving like a grandma away from everyone.
Thank you... absolutely. My wife is really pissed because she thinks the care is insanely unsafe and that she's going to get T-Boned by someone in a "Tampa truck" (one of those huge Ford F-250 pickups with the lift kit). I told her, it's really no more unsafe than any other car, but she might be right, and I am a little concerned. I do know that being in a small car is often safer than being in a big car because you can get away from stuff and better avoid things.
But, we'll see... I'm making arrangements to pick it up next weekend.
Originally posted by 82-T/A [At Work]: Thank you... absolutely. My wife is really pissed because she thinks the care is insanely unsafe and that she's going to get T-Boned by someone in a "Tampa truck" (one of those huge Ford F-250 pickups with the lift kit). I told her, it's really no more unsafe than any other car, but she might be right, and I am a little concerned. I do know that being in a small car is often safer than being in a big car because you can get away from stuff and better avoid things.
But, we'll see... I'm making arrangements to pick it up next weekend.
Its a justified fear.
Do remember this is one of the safest non airbag cars ever built. Stronger than strong subframe. But those stupid trucks tend to go up and over these cars.
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. If you daughter is mature and gets the message, I wouldn't be concerned about any danger.
Plus she will never end up with a drug addiction, because the Fiero parts will make sure she can't afford any 😂.
We welcome her to the Fiero Family
------------------ My girlfriend said she's is gonna leave me if I buy one more car, I sure am gonna miss her.
While that's good information to build a tach filter. 82-T/A's documentation shows that my assumption this was related to the tach was wrong. The tach filter is on the white wire after the ICM. This doodad is on the 12V purple and black wire before the ICM.
Every Fiero 2.5/2.8 engine (except the the distributorless '87-'88 L4) apparently requires a tach filter. I wouldn't completely dismiss the idea that this "doodad" isn't a tach filter for the '84... because if it isn't, then what is and/or where is the tach filter on an '84?
I don't think this is the silver bullet you think it is...
"silver bullet"? I have no idea what you're referring to.
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Originally posted by 82-T/A [At Work]:
I do think the "new and improved" one that we now think came with the 84 is still a better design, and I'd like to emphasize that. But just want to be clear on it.
There was never any disagreement on that. For both the 2.5 and 2.8 engines, the "newer" style distributor (which in reality was the older original style) is superior.
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Originally posted by 82-T/A [At Work]:
I will admit when I'm wrong, and you've converted me. I believe you, and I apologize! Hahah... damn you!
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!
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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).]
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).]
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!
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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).]
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
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.
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
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.
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)
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).]
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?
Googled the 7 digit GM part # and found a cross reference for it
[This message has been edited by maryjane (edited 02-25-2023).]
Googled the 7 digit GM part # and found a cross reference for it.
I think perhaps I was too fixated on T8349, but even when I now do a search for 1987569, I don't seem to find anything of any relevance. I'm impressed by your google skillz!
"silver bullet"? I have no idea what you're referring to.
Well, "I" believe you, I was just looking for something a bit more concrete like a picture of an original duke engine so I could include it on my page for reference.
I haven't updated my website in a long time... like, a decade really except for two pictures I added. Half the images are broken because I went from a Windows-based hosting to a Linux-based hosting... but I do want to start updating it again.
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.
Shoot. My radio works fine, but if I use a Bluetooth transmitter I get that whine. Probably because it's in the cigarette lighter and shares the same circuit.
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
I wanted to bump this again... just because the Pontiac Service Manual (for the 1987 Fiero) arrived at my house this morning. I am blown away... I don't even want to touch it for fear I'll put fingerprints on it. I almost wonder if I should buy another because it's so awesome... and I want one for my bookshelf and one for the garage! hahah...
Anyway, the books are absolutely FANTASTIC. The 87 comes as two books. There are no page numbers because they go by sections, but I'd have to assume that each book is about 700 pages. They are each enormous. It literally covers everything you could conceive of.
I am not sure if they are originals, or if they are reproductions... because the cover and everything is exactly like the originals from what I can see; however, some of the fine print... like the Brake Diagnostics Chart gets a little grainy. It uses some small print which is clear everywhere else, but on a couple of the charts it gets just a tad fuzzy... which leads me to beleive it was a scan. Still, it's 100% legible, and only looks perhaps 10% degraded from everything else in the book which is completely clear and pristine (as if printed directly from text, and not a scan).
The books are fantastic. I may even end up buying one for my 1985 since I just bought another Fiero. If you can swing it... I definitely recommend it. 1984 is the craziest (but one of the coolest) years, in my opinion.
My TPS is reporting 1.2V at a fully closed pedal, which seems a bit high. lol. It looks like I got a bad TPS right out of the box. Gonna to find me a good delco unit.
Does anyone know what good O2 Sensor readings should be. Mine seems to bounce around a lot.
My TPS is reporting 1.2V at a fully closed pedal, which seems a bit high. lol. It looks like I got a bad TPS right out of the box. Gonna to find me a good delco unit.
With the presumption that your throttle is closed as far as it should be... try adjusting your TPS. No, don't bend the tang. Watch/listen to the way the fella in this video does it. (Jump to 2:49) He rotates the TPS. If your TPS isn't slotted, break out the Dremel...
In regards to your O2 sensor, the reading is supposed to bounce around... but hopefully someone else can provide further details on its proper operation.
[This message has been edited by Patrick (edited 03-21-2023).]
My TPS is reporting 1.2V at a fully closed pedal, which seems a bit high. lol. It looks like I got a bad TPS right out of the box. Gonna to find me a good delco unit.
Does anyone know what good O2 Sensor readings should be. Mine seems to bounce around a lot.
The factory service manual says that the TPS signal will vary from less than 1.25 volts at idle to 4.5 volts at WOT. I'd infer that 1.2 volts at idle is ok.
The O2 sensor should be bouncing around 0.45 volts if the engine is running at stoichiometric air fuel ratio. Look at the integrator reading these should be bouncing around 128 if everything is normal. The integrator is the short term fuel trim and is responding to the O2 sensor. The long term fuel trim (BLM) should also be around 128 if everything is normal. The BLM values are adjusted by the integrator to try to keep the integrator around 128.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
[This message has been edited by sanderson231 (edited 02-28-2023).]
Resistance in the ground circuit from the TPS to the ECM could cause the TPS to read high at idle. Make sure the connections are clean.
Without going through this entire thread again, I've also been wondering if grounds have been addressed. Lack of proper ground(s) can cause all sorts of issues.
Although the following thread is directed at the 2.8, a lot of it certainly applies to the duke.
After adding the grounding wire, the Fiero was transformed from a stumbling starter to the Magnificent Beast God intended it to be! I also lost 5 pounds, added another inch to the stickshift, and got a smile from the secretary who lives next door. Who knew a piece of wire could make such a difference!
[This message has been edited by Patrick (edited 02-28-2023).]
I have not checked grounds. Probably a good idea since this engine has been in and out 4 times.
I did notice that BLM stays pretty consistent at 128 when "idling" but as soon as you tap the gas it bumps to 140 and stays there.
Its currently raining, wet and depressing out right now. Hopefully signing a lease on a new shop today. Then I can get to work on the grounds. Will keep everyone posted.
Here are the basics of how the fuel injectors are controlled and how the system self tunes. This is for part throttle operation where the system is in closed loop. The fuel injectors are controlled with pulses of 12V. The wider the pulse the more fuel flow. This is known as pulse width modulation (PWM).
There are 16 BLM cells arranged in a grid. Which cell the ECM is in depends on the rpm and MAP (manifold absolute pressure). So at idle the ECM is in a certain BLM cell. As the engine rpm's move up and MAP increases (less vacuum) the ECM moves to a different BLM cell. The BLM value provide for feed forward control. They give a starting point for the fuel injector pulses as the engine moves to different rpm's and MAP.
The O2 sensor provides for feed back control (closed loop). The sensor reads the O2 in exhaust and outputs a voltage signal which goes to the integrator. If the O2 sensor sees a lean condition, the integrator will add fuel injector pulse width and the integrator value will be above 128. If the O2 sensor sees a rich condition the integrator will subtract fuel injector pulse width and the integrator value will be below 128. The longer the O2 sensor voltage deviates from 0.45V the more the integrator will increase or decrease (hence the name integrator).
If the integrator values average 128 the BLM values will not change. If the integrator stays above 128, the BLM value for the BLM cell will slowly increase. Since the BLM is now adding fuel, less fuel addition is need from the integrator. The BLM value will continue to increase until the integrator is averaging 128. So with a BLM value of 140 it means that at that particular rpm and MAP, the integrator has had to bias up the BLM value. This indicates that the something is not as expected and the ECM has had to compensate. It could be a partially plugged fuel injector, low fuel pressure, vacuum leak and other things. As long as the integrator and BLM values stay with their control range (IIRC 108 to 154) the engine will run at stoichiometric air fuel ratio (about 0.5% O2 in the exhaust) while in closed loop. So to get a good picture of what might to causing the ECM to compensate, the ECM needs to be datalogged over a range of operating conditions
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
Pretty sure the Tach filter is to smooth out the signal going to the tach needle itself so it does not jump around, seems like the other cap is to smooth the signal to the ICM?
When you set timing, did you jump the pins in the OBD connector? Timing will be wrong otherwise.
Can you hook your TPS up to an oscilliscope and make sure it isn't jumping as you rotate it?
Does your dist have any play? Is there play in the shaft? Play in the rotor? Is the spring loaded pin in the distributor cap working properly? Have had that one cause all kinds of issues. Have you checked plug wires to make sure none are arcing?
Check power to the ECU, there are two pins that splice together into one wire that goes all the way to the junction block below C500 on an 85. There is a single pin connector inline at the junction so you can reset the ECU. This line went bad on me and caused all kinds of weird intermittent problems.
Check your C203 for corroded pins, I found a couple there.
Hook up a fuel pressure tester before the TBI, you can rent at Azone, and point a gopro at it while you drive.
To me, backfiring is an indication of timing getting messed up, but it could also be TPS related. A lot of brand new off brand components just don't work right out of the box.
I have no idea what you're referring to.
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.
