89 Firebird Turbo 3500 Build

[robertisaar]

a misfire on a consistent cylinder doesn't sound like a tune issue.... it's not like there are cylinder specific fuel trims or spark mods or anything like that...

at least it's been narrowed down to a spark related issue fairly quickly.

[caffeine]

I got it idling fairly well on nAst1 but a misfire is still there and seems to get worse the longer I run it. I just replaced the plug wires today and no change. I'm wondering if its just the tune or if there's something else wrong. I can upload a datalog tonight.

[robertisaar]

F163, F164, F165, F166, F113 tables.

considering how large the injectors are that you're running, i'm kind of amazed you didn't have to significantly reduce the values to get it to start cold.

F164 would be a good place to do most if not all of the changes. divide the values by 3 compared to the stock 3.1 tune.

[caffeine]

Here's the latest bin and two logs. Both times the car stalled on its own after running a bit. Wideband dipped lean whenever i heard a pop (misfiring). Also when I went to start it after it stalled the first time, I couldn't get it to fire until I unplugged the fuel pump relay. Is there any way I can reduce fueling while cranking?

3500T Startup.zip

[robertisaar]

C21 is originally used for A/C pressure sensor, so you can modify the ADX to have it displayed there easily.

the exact conversion required will depend on what your WB controller outputs.

also, below 400RPM(in a stock calibration), the ECM doesn't control anything timing related, the ICM does it all(dwell and timing).

[caffeine]

Puzzling indeed, sometimes we need to walk away and let the solution break through while relaxing.

Down to the spark issue.....I would do what PRocket suggested, how it behaves could tell a lot. Start swapping things around like coil packs, plug wires, plugs, etc. to see how the problem reacts.

It may be possible the ICM is failing and is aggravated by being bolted down. Is it possible the rig on the Fiero was not as hard on the ICM?

Maybe try temp cutting the wire to the PCM that allows the PCM to take control of ignition timing and see if it makes any difference. I don't like cutting wires but it is an idea to see if the PCM is failing. (If your PCM works in such a way, I don't remember your setup)

As shown in the video, I've been testing spark right at the post on the coil. So if plugs or plug wires are a problem, its not the only one.

As for the ICM/coils, when I swapped them from the Fiero I swapped the mounting bracket as well so the ICM was bolted down just as hard. They're mounted exactly the same way.

If the ECM was the problem, I don't see why it would show up during cranking, but could be wrong. I would expect it to at least show something in the log though.

[caffeine]

which pin is that?

C21 I think

[TGP37]

Puzzling indeed, sometimes we need to walk away and let the solution break through while relaxing.

Down to the spark issue.....I would do what PRocket suggested, how it behaves could tell a lot. Start swapping things around like coil packs, plug wires, plugs, etc. to see how the problem reacts.

It may be possible the ICM is failing and is aggravated by being bolted down. Is it possible the rig on the Fiero was not as hard on the ICM?

Maybe try temp cutting the wire to the PCM that allows the PCM to take control of ignition timing and see if it makes any difference. I don't like cutting wires but it is an idea to see if the PCM is failing. (If your PCM works in such a way, I don't remember your setup)

[robertisaar]

which pin is that?

[caffeine]

I got it to idle on nAst1 but it stalled both times after a minute or two. I'll post up the logs and revised bin later. To get it to start the second time I had to unplug the fuel pump relay which I'm assuming means it was dumping way too much fuel during cranking.

I think im going to try stripping the paint off the ICM mounting bracket to see if that makes any difference. Strange thing is that I tried the Fiero bracket as well (which is essentially the same) and it made no difference yesterday. The last time I ran it it sounded like it was misfiring less but its really hard to say. AFR on the wideband was around 11.5.

Which reminds me, I have the wideband also wired the the pin which is used with code59 for logging, how do I see that when logging with nAst1? I also have a stock narrowband wired to the computer.

[caffeine]

Added a ground strap directly from the ICM mounting bracket to the battery. Started up and ran well for a bit, then the misfire returned. I uploaded a video of the spark tester showing the intermittent spark on post #5:

http://youtu.be/a5x_TtJmfPo

[caffeine]

My wifes old Daewoo had a gm engine/electronics.

The coil pack went bad once, and it had waste spark. It was 2 coils in one package. When it failed, it grounded one tower internally so only 3 plugs fired. But then again, he said the coil worked fine on the Fiero earlier. Have you swapped wires/plugs around to see if the problem follows?

I've been testing the spark at the coil post so I know its happening there at least. All the ignition parts went back on the Fiero and are still fine. I tried swapping the crank pos. sensor and wiring as well.

What I'm seeing with the spark tester is that when testing during cranking, all posts except #5 spark at a steady, regular pace, and #5 sparks at an irregular pace, sometimes almost half speed of the others.

As for grounds from engine-chassis, I'm going to try adding some ground straps. I figured that the solid steel motor mounts would be sufficient but I'm running out of ideas.

[pocket-rocket]

My wifes old Daewoo had a gm engine/electronics.

The coil pack went bad once, and it had waste spark. It was 2 coils in one package. When it failed, it grounded one tower internally so only 3 plugs fired. But then again, he said the coil worked fine on the Fiero earlier. Have you swapped wires/plugs around to see if the problem follows?

[TGP37]

Your main ground to the block, is it bolted to the trans bellhousing or the block itself? Test and see how much resistance you get from the battery - wire terminal to a cylinder head. Are there any non or poor conducting materials between the trans housing and the block?

Probably fine, though resisting grounds can cause issues.

If #5 is bad and #2 is good, that IS weird as both #2 & 5 should fail if either fails. They are opposing ends of the same coil inside. When one plug sparks to the ground, the other sparks from the ground in the opposite direction. pic


Checked the plug wire resistance yet?

Try running a new ground from the ICM to the batt-? To test the ground circuit.

Spark plug port threads coated or dirty on #5?


I doubt the 7x crank sensor is wired backwards as it would run even worse, if at all. But is worth checking. My VSS and 7xCKP pigtails are identical except for polarity.......if you custom wired, did you shield the crank sensor wire? Needs 12 twists per foot.

What about the wire which lets the PCM take control of spark from the ICM after start up?



A lot I mentioned I'm sure you know already.......just offering ideas, brain storming.

[caffeine]

Just tested resistance on the 5-wire pigtail and none of the wires are showing resistance. Also tried the crank sensor and crank sensor wiring from the Fiero. No difference. This is driving me crazy!