Posting to this forum as this is an engine you guys know much better than the Fiero guys would - it's a speed-density 350 TPI running a '92 8262 ECM, essentially a 7730 w/$8D map. I built it 20 years ago and it's been sitting for about the last 10 years, and I've been trying to get it running properly again. it ran well as recently as three years ago and this happened suddenly while taking it out for a drive. It's not reporting any codes at the ECM, just flashing 12's. I know that generally points to an ignition problem. It starts up immediately, but has a rough idle and is sluggish to rev. It's drivable but is cantankerous at best, with backfires. I've recently put new cats in it and it just has bullet mufflers that shouldn't clog.

This is a TRUE DUAL EXHAUST with headers, dual cats and dual mufflers with ONE ACDelco O2 sensor on the front (odd) bank only.

First step - Replaced all injectors
Second step - drained fuel tank and refreshed with 5 gallons of premium
Third step - replaced distributor cap
Fourth step - new plug wires
Fifth step - look for vacuum leaks with propane torch. Replaced a few aged hoses around the cruise control, but no apparent leaks.

Since starting this thread, the following critical observation has been made:

Even (rear) bank (2,4,6,8) exhaust is blowing cold, fuel-saturated air, and warms up slowly.

Additional diagnostic steps performed in this thread:

6. Disconnected entire rear bank of injectors. Runs the same.
7. Checked plugs in rear bank. Good, but wet with unburned fuel.
8. Replaced ICM. No change.
9. Tested spark with spark tester at distributor. Tests good.
10. Ran compression check on rear bank. OK at 135-145 across all four.
11. Connected MT2500 scanner to ECM. Once going into closed loop, Integrator goes to 129 and BLM goes to 136, but the ECM otherwise thinks everything is fine on the front bank. No O2 sensor in rear bank.
12. Checked injector fuses, all OK.
13. Injector wiring tested. All red wires on injector harness tested good +12V to ground, and no shorts to ground on any injector harness dark green wires.
14, Verified plug wires match firing order.
15. Cleaned and re-gapped spark plugs to .035.
16. Ran compression check on front bank. OK, 155-175 across all four.
17. Removed and cleaned ECM, Moates adapter, CALPAK and flash EEPROM connections.

I have a replacement rotor for the distributor, but the original wasn't coming off and I didn't want to make it worse trying to force it, so I cleaned it up with some emery cloth and stuck with it for now.

Plugs are NGK R's and are properly gapped at .035.

None of these fixes has made any difference and the issue persists. I recorded a short video so you guys can see & hear what it's doing.


Suggestions for next steps welcome.

 

Additional info I forgot to mention on the fuel side, there is a new fuel filter, and there is a pressure gage on the fuel rail that shows the pump primes to about 42psi with the regulator vac line on, goes to about 48psi with it off (running), so I think that's good fuel pressure & regulator. I have a Snap-On scan tool that I can use to do live readings, but I don't know if I can do logs at this point due to cabling/connector issues.

 

does that intake have a egr valve? I had one stick open forever ago and it ran rough.


what intake is that? it seems to idle OK, does it just not Rev? can you watch the fuel pressure while revving it?

byond that, maybe check the timing bypass isn't unplugged? what computer is in and how's it tuned.

 

No EGR. S&P Ram-Port intake. Not idling OK at all, jumping back & forth between 800-900rpm. Timing bypass is not enabled. 8262 ECM custom-tuned in 2004.

 

I had to Google that ecm number. seems it's a newer Rev of what is normally a 7730 ecm. so should be a standard $8D map tune in it.

is the check engine light wired up correctly? I'm asking cause I'm guessing it's not a stock harness in there. if so, there's a way to check that the ecm is in "limp" home mode. it's been forever and my memory is bad. so you may want to search it. but if you click the key to on but don't start it, the fans kick on high and the check engine light doesn't so something, I don't remember what. maybe go out after it's check? the ecm isn't reading the tune off the chip and it is running off a very base map. but mine would actually idle and stay running even with bigger injectors.
​​​​​​I believe in this mode a scanner also can't connect to see live data either. which I should ask, do you have a scanner. if it's not in limp, data might help to know why it's running badly.

you may want to start a thread over in the DFI/ECM sub forum. might get more eyes on your post over there.

 

Correct, 8262 is newer 7730 with $8D map. Check engine light is wired up correctly and is indicating properly. Painless wiring harness FYI. ECM is not in limp-home mode. I have a Snap-on MT2500 scanner.

 

New video from scanner. Looks like it doesn't want to go into closed loop for some reason.

 

Went at it again today and have some new observations. It eventually went into closed loop after getting up to temp. BLM then went to 136 and integrator to 129. While the left side exhaust is hot and loud, The right side exhaust is blowing cold and quiet with slight bluish smoke when revved. It looks like the right side (rear bank) is basically not firing at all. I'm trying to figure out what would cause that to happen.

 

Pulled all four rear bank plugs. All four wet and gassy but otherwise properly gapped and fine. I can't figure out why this would happen, but it seems to point to the ICM. But would only one side of it fail?

 

I would have to look up wiring diagram. I seem to remember the 7730 ecm only had one injector driver and opened all 8 in a batch fire ground side. but I think there was 2 different postive wirings? if you have a noid light you can check to see if the back injectors are flashing right, not stuck on it off?


unless you just don't have spark, but with a distributor. I can't think of anyone half the plugs get power and other half doesn't.

 

Right side exhaust is cold and gassy. The rear bank just doesn't seem to be firing at all

Replaced ICM. No change.

 

Because it's on one side, I don't think it's anything ignition related. Ignition uses 1 p/u coil, 1 ICM, 1 coil, 1 rotor, 1 cap....I doubt that you have 4 good wires/plugs and 4 bad...all on one side or the other.

I'd start looking at mechanical issues. Pull that rear valve cover and watch the rockers rock.

You can visually check spark, too, on that bank. One blown injector fuse would make one bank be dead....but that flies in the face of "wet and gassy". I'd still check it.

EDIT: Check the harness for the right (rear) bank injector to ECM wire short to ground.....could be flooding the bejeezus our of the rear bank.

 

LOVE the V8 Fiero GT, BTW. LOVE it!

 

I tried disconnecting all four rear bank injectors and it ran exactly the same. Uploaded a video of the rockers moving while cranking here.

 

Seems like you need to focus in on that right injector bank. Power, ground signal through the ECM.

 

Fuel delivery doesn't seem to be the problem as much as spark, or the complete lack of it.

 

Yeah? You tested spark? And had none only on one side of the engine?

 

Yes, and very much mistaken. Spark tests good on the rear bank.

 

Copy. That makes more sense. Thanks for clarifying. Haven't checked both inj fuses yet?

 

Also check the pinning in the harness. I believe the later SD harness may have also had separate negative wiring back to the ECM, even though there are tied AT the ECM.

 

Yes check the injector fuses because it's simple and easy to do and makes sense to do.

If you have enough slack in the fuel injector wiring harness flip flop them by swapping the back & front bank harness and seeing what happens.

If the back bank starts working and the front bank quits working then you know the back bank's injectors are working and the problems is somewhere between the injector connectors on the harness back to the injector driver on the ECM.

If the problem stays the same with the fuel injector harness swapped front to back then you have some kind of problem on the back bank.

10 years ago the engine did run and I assume it ran on all 8 cylinders. Then it sat for 10 years. Rodents could have chewed on the wiring. Corrosion could have grown on connections and in the wiring harness. Maybe by some chance all 4 injectors on the back bank locked up. The inlet screens on the 4 back injectors could be clogged up with dead ants. LoL

 

Fuses test good.

 

As my memory of everything has been coming back to me on this situation, it actually ran well as recently as 3 years ago. This happened suddenly in June 2021.

Not enough slack to swap the injector wiring front to back.

I found my compression test gauge and can run a comp check on it. I feel like that's the logical next step, but it would also be strange to find low/no compression on an entire bank.

 

The odds of all 4 injectors being bad or all 4 cylinders having something wrong with them on the same bank are slim to none.

The odds of a mouse chewing through a wire on the injector harness for the back bank of cylinders, a wire that got pinched or cut in two, loose connection/bad connection, or corrosion on connections or in the wire is way better odds.

 

While I appreciate your suggestion, I have no idea how to translate this into a plan of action with this configuration

 

Ran a compression test on the rear bank.

Results:

#8: 145
#6: 140
#4: 135
#2: 135

Test performed removing 1 plug at a time, cranking for 2 seconds and checking results. I know it's not ideal but I'm doing it solo and don't want to mix up the plug wires.

So, that's a huge relief.

 

Your plan of action is trace every single wire related to the rear bank of fuel injectors from the fuel injector connectors on the harness to the pins in the ECM and inspect them for any kind of damage. You're going to need a Digital VOM and eyes, knees, back, and neck of a teenager. Wouldn't hurt if before you started all that you had a noid light test set and could test to see if the injectors are even getting fire.

PITTSBURGH AUTOMOTIVE Noid Light and IAC Tester Set 11 Pc - $29.99

AMES INSTRUMENTS DM600 Compact Digital Multimeter - $42.99

 

I'd amend the recommendation about "tracing every single wire", though. They're all tied together on each side.





All you really need to do is check for power w/key on, at any or several of the female pins on 2/4/6/8 at the inj plugs that correspond w/the pink/black wires...they should all have power, all the time, key on.

THEN, using the meter, test for shorts to ground, or an open between pin C11 on the ECM, and any of the injector plug pins that correspond with a dark green wire.

Since all the powers and all of the grounds are tied together, if any of them are open or shorted to ground (or shorted to power), then all of the injectors on that one side, will be.

 

All red wires on injector harness tested good +12V to ground.

No shorts to ground on any injector harness dark green wires.

Looks like that can be ruled out then.

 

noid light would be worth checking.


how about at the ecm, depin and swap the injector grounds and see if to switches banks.

that could rule out harnesse?

depin is each with a paper clip. there's a thread around here somewhere. but stick it on the top hole and pull the wire out the back and swap, pop back in.


you definitely have a weird one going on. I'm pretty sure there's only one injector driver in the ecm, but since it goes to 2 different pin locations, maybe a trace on a board isn't making good connections. in fact thst is kinda what it feels like since they are wet with fuel, but not firing correctly enough to run. maybe it's intermittent.

 

^That is a pretty wicked idea. I love it!

 

C11 & C12 on the larger black connector on ecm.

 

I really like this idea too. The problem might actually be right there in the connector. A terminal might have worked its way loose de-pinning itself or could be corrosion in the connection between the two connectors

 

is it an under hood ecm? cause I was picturing inside the car ecm.


either way, if you listen to the video, I don't think the whole bank is 100% dead. I've never done but I doubt I could pull all 4 injectors and the thing start and run. in the video I thought it was idling fine. he said it's different then what it was thou.

 

ECM is actually in the trunk and is piggybacked to the stock one inside the car. Yes, it runs two ECMs. It runs the same with the rear bank's injectors disconnected.

Just to be sure, today I went back and verified the plug wires correlate with the firing order. All matched up to 1-8-4-3-6-5-7-2.

 

huh. so I v8 will run on only 4 cyl. I didn't know.


then I think I'd swap the pins at the ecm and see if the bad bank swaps too. if it does ecm issue. if it doesn't either harness somehow or spark. which I still have no idea how only one side spark and the other doesn't.


the back bank are the plugs hard to get to? I once used an electric ratchet putting plugs in a Ford truck. fired it up and it missed all over the place. turns out I put hair line cracks in a few of them. from then on ive been careful to do plugs by hand and not pull on the ratchet. try to keep centered.

 

I'm still in agreement with ???'s idea of swapping the ground wires on the ECM for the injectors...
....but I got thinking and thought this...
Is it possible an animal built a nest or something (died) in the rear bank's exhaust...and that side is completely plugged? That'd give you wet plugs, but essentially no fire on that side.

 

It's a great thought, Tom, but I don't think that would be the case here as I remembered that this actually happened suddenly while taking it for a drive three years ago and it had been running great up to that point.

I haven't found any evidence of rodent invasion anywhere in the car so far, and I've been pretty thorough going through it the past couple weeks. And honestly there's really not many places that rodents can go in these cars without you knowing or seeing it.

 

Both sides, plugs are easy to access from below. I always hand-thread them all the way down and apply final torque to spec with a Craftsman torque wrench. It's aluminum heads, not taking any chances. Had a Ford Triton 5.4 launch a plug once, and it required a head replacement because a previous owner had overtorqued it.

 

How hard is it to get to the 7730 ECM in your Fiero GT and de-pin those two terminals and swap them like ??? suggested?

 

Just curious, has the fuel psi regulator failed? Shooting raw fuel through the vacuum line into the intake? Maybe it fouled the plugs that aren't firing?

 

Accessing the 8262 ECM is easy in the trunk and I am going to take a look at doing this tomorrow.

 

I have an adjustable regulator mounted to the fuel rail next to the pressure gage and easily accessible. Is there a way to test this?

 

Pull the vacuum hose off the fuel pressure regulator and see if fuel runs out. If not smell it and see if it smells like gas. There should be no gas or smell of gas on that side of the fuel pressure regulator.

 

Distributor question: does it matter if the large ring that sits between the rotor and the ICM moves? I can rotate it maybe 10 degrees independently of the main shaft before it stops.


TPI distributor

 

If you are talking about the copper brass looking piece then no it doesn't matter if it can rotate around that much. I forget what that part is called and a lot of these small cap HEIs didn't even have that part when new. It was added at some point along the years. I have a 27k mile one I removed from a 1990 Formula 350 and that distributor doesn't even have that copper brass looking piece. It's a shield of some kind. Maybe for EMI or maybe some attempt to prevent them rusting and corroding to death inside. These distributors really should have had a vented cap.

I just checked an NOS new one, a 3900 mile one from a RamJet 350 crate engine, and another low miles one I removed from something I've forgot now and that piece can rotate around a decent amount of degrees.

 

Thanks Airwolfe, you'd definitely be the guy to know about that! Well that's one more potential thing to cross off the list. Is there a trick to getting the rotor off? I've tried prying it every which way I can think of without damaging it but it just doesn't want to come off.

 

Just pull like Hell straight up on it and be prepared for where your hands are going to fly off to when it lets loose. You might take and small handle screwdriver or something and peck on the round base of the rotor button with the handle up under the rotor button where it pushes on top of the shaft to help break it loose some. Even brand spanking new they are on pretty snug.

 

Plugs #2 & #8

First two plugs I took out for cleaning with a new HF plug cleaner I mounted up this morning. #4 & #6 looked about the same.

 

OMG is that an abrasive media blaster that uses garnet sand to blast the sparkplugs clean? I'd very closely inspect them with a bright focused light to make sure there isn't a speck of abrasive media down inside them or on the threads or anywhere on them before installing them. With your aluminum heads I'd also put some anti-seize on the threads because the blasting media might have stripped off the special coating/smooth finish that was on the threads of the plugs when new.

Wow have sparkplugs got so expensive now that people are having to blast them clean instead of get new ones?