1988 Camaro V6 severe ongoing misfire issure

I finally made it here after some more throwing parts at this thing and scratching my head after viewing some of the YouTube videos...

Problem: Ongoing misfire that seems to be random in all 6 cylinders with no seemingly common cause.
Vehicle: 1988 Camaro 3.1L V6 LH0, manual transmission. Running on 2.8 engine control system with 1227302 ECM.
Started mostly after a bad head gasket replacement on 1-3-5 side of the engine (both head gaskets replaced but the bad one was in cylinder 3).

I have the factory service manuals and a technical background. Flow charts lead me nowhere because the engine starts and runs but misfires with no trouble codes. I do not have a scope but have access to a Tech I through the dealer I work at (when I can find the thing).

All voltages check out throughout the ignition system and up to the fuel injectors. The misfire occurs whether or not the ECM is controlling timing or the Set Timing (EST Bypass) connector is unplugged. I have a high idle because I can't set it down to the 650 RPM it's supposed to be at because it's not stable enough to run at that low idle speed. I have no vacuum leaks. I have checked the compression and reset the valves in all 6 cylinders because it was suggested I either have valve float or a broken spring (nope, no broken springs). Compression is about 180 PSI in all cylinders. Fuel pressure 41 PSI running. I have a cleanable fuel filter that was not only cleaned but replaced when this problem started up. Fuel pump is aftermarket Bosch external pump I haven't had issues with since installing. Tach bounces. Engine shakes. Again, no trouble codes. I have 3 timing marks on the damper and they are all a different color so I can watch the coil firings with my timing light. 1/4 white, 2/5 red, 3/6 blue. I'm occasionally seeing the other colors when watching the firing on whatever cylinder (generally #2 sometimes #3). I have a couple videos I have taken of this.

I do have trouble with cold starts... Because the cold start injector doesn't work and finding a replacement is proving impossible since nobody makes them and both of the used ones I have are both clogged or stuck internally even though they are electrically sound (yes, they click). Hot starts are no issue once the fuel pump starts running (I don't have a check valve in the system). One problem I have been having with these cars is the fact that starting idle speed likes to jump up to somewhere around 2400 right after start and then take its sweet time getting back down to whatever idle speed again. Not sure what the deal is there as I have swapped between several IAC valves and they all do the same thing. One ECM is a little faster than the other but they're both slow. It's not an "idle flare" thing... That's almost instant. This is much longer duration.

So far, I have replaced the following parts:
3 sets of fuel injectors (one OEM I won't mention how I got, one "reman" and one brand new that is currently on the car)
2 sets of spark plugs
2 sets of ignition wires
Distributor cap and rotor
Ignition coil. Primary side wiring between control side of coil and ignition module was repaired due to break in the wire near the middle. Ohms tested to 0.01 just a couple weeks ago.
I have 3 ignition control modules, one GM/Delco, all 3 have the same issue
Distributor in the engine now has been totally rebuilt with all GM parts (ICM, pickup coil, and even the entire main shaft due to finding cracked magnet)
Distributor I pulled out of engine to install GM rebuilt was BRAND NEW a month ago
Mass Airflow Sensor and MAF relay. I probably should replace the connector but haven't gotten there yet. It's not currently throwing a code 34 so I suppose it at least partially works. And the MAF is a Genuine GM MAF (I have had issues with aftermarket in the past so I don't do that any more).
I have also swapped a couple IAC valves for other reasons.
EGR valve was found to have bent shaft and was replaced. EGR vacuum switch assembly was replaced because it wasn't working and throwing a code 32. Don't know if it works as I haven't been able to drive the car at all much less long enough to see if it would throw the code.
I have also swapped the ECM for another one I had from the old Bird, also a 1227302. The better running ECM has the proper 1987 calibrator chip set in it (control system is from my old 87). The other ECM has the recall calibrator chip in it for the "Stall, Sag, Hesitation After Cold Start" TSB.
I have also modified the fuel pressure regulator for more pressure and less pressure. To no effect. Helped me find out my pressure gauge is off by 8 PSI... Ugh.
Also today installed spark plug wire separators when I swapped in the distributor. Also turned the firing order 180* to where the factory manual wants it to reduce crossed plug wires.

Okay, so I have basically done everything I can think of. I have 6 spark plugs that are all the normal light tan with no deposits now that I have the new injectors. I have been fighting this for months. Right now, I am borrowing a car because I can't drive this thing (and my sister has my other one). It's already overdue for annual inspection. I'm really scratching my head on this because everything except the wiring between the ECM and distributor and fuel injectors is either pretty close to or is brand new. I built this car from a bare frame from my 87 that was a rust bucket that got 30+ MPG and this thing can't even hardly leave the driveway. It's only had about 300 miles on it since I swapped out the blown engine last May.

Any and all suggestions appreciated and I need to get this done soon. Keep in mind the only way I would have access to a scope is by getting the car to the dealer I work at (and neither I or anyone there knows how to hook it up... it's a Snap-On we got a little over a year ago). I've been wanting to go and get it hooked up but I'm not sure how.

this started out with the headgasket being replaced? was it burning coolant thats why you changed it?? maybe the converter is damaged and is restricted on that bank. have you checked back pressure?

how does it run while holding the throttle at higher rpms?? also is the vacuum steady on a gauge??

If the tacho is jumping out of synch with the RPM to me it points to a problem on the low tension (primary) side of the ignition it could be an intermittent bad connection in the 12v supply or related to the position senor or its wiring.

1. Cat is gutted. Yes, I was slightly burning coolant in cylinder 3, which had a cylinder pressure test of 87 PSI while the others had 180ish when I replaced the head gaskets.
2. Don't have a position sensor on a distributor ignition system and the pickup coil is brand new GM as I stated before along with the ignition module. Voltage tests at battery voltage both at coil power connector and coil to module connector. Pickup coil has ohms tested within GM specifications, both the new one and the old ones (of which there are 2). I have already examined the pickup reluctor for any damage and found nothing.
3. Runs smoother at higher engine speeds with occasional hiccup. Tach goes off scale before actual engine speed hits 3000 RPM. I forgot to mention before I am running a dashboard and instrument cluster from a 94 Camaro that had the 3.4 V6 equipped with distributorless ignition. I expect the tach to not read properly (already know I need to install a tach filter but getting the misfire fixed is higher priority than getting the tach working right) but it shouldn't bounce, should it?

Since my multimeter(s) have the ability to read frequency, anyone have any idea as to what frequency I should be reading off the coil TACH connector at about 1200 RPM? Is it 7200 or 3600 Hz, assuming 6 pulses per cam revolution? I'd like to compare that to the output of the module connector and see what happens... I already know that the ECM reads the engine speed from the ignition module while the tach reads from the negative side of the coil. And I also know that the ECM sees a pretty steady engine speed (as in, no mysterious jumps to 3000 RPM like tach is showing at idle) via watching with the Tech I.

Have you looked at oxygen sensor MV, or fuel trims?

There's an article about 2 injector fuses. One might be blown, but will appear good with test light due to shared circuit inside pcm. Pull them both and check.

Severe misfire / engine performance diagnosis should be easy. Start from scratch at the basics. Compression, fuel, ignition, and ability to breathe. Try to isolate problem cylinders by doing a power balance test. Unplug injectors and note the ones affecting engine speed, preferably on a scan tool or tac. (Timing light..) if none affect it noticeably then you have a big enough problem affecting all cylinders, probably in the air fuel ratio side of things.

Maybe a running compression test, might show something. Here's how to interpret readings.

Running compression test

I've seen a harmonic balancer that was basically in two pieces, caused a shake so bad I thought it was about to blast into space.

Take a step back and start fresh. The answer is there.. Somewhere. Good luck

1. Power balance test has already been done, 2 months ago. Watching the Tech I (which I no longer have access to at the moment), each cylinder registered a drop of 50 RPM. Both between disabling spark and unplugging the fuel injectors.
2. Watching BLM and Block Learn isn't going to help me any at the moment as I have a small exhaust leak on the 1-3-5 side of the engine and a couple pinholes right next to the O2S (I had to basically replace the bung last year and left a couple pinholes I haven't fixed yet). I haven't been able to check the O2S mV since installing this latest set of injectors a couple weeks ago because the Tech I is inaccessible. It had been running mostly lean but not overly lean (as in it was capable of switching between rich and lean). And I have been taking direct contact temperature readings at the exhaust manifolds, which are all with 10* when warmed up now that I have the new injectors in. The temps had been all over the place with the other sets, generally ending up with cylinder 1 being down and other one being down as well.
3. I built the dash harness. I am aware there are 2 dash fuses for the fuel injectors. Thought I had separated them from the ECM ignition circuit but the 2-4-6 side seems to be on the same circuit as the ECM... I have power on both injector banks.
4. Having a goofy damper wouldn't cause a misfire coming out of the tailpipe... I know how bad an out of balance engine shakes (I have misaligned the timing on the balance carrier assembly from a Chrysler 2.5) and this isn't it. The balance weight is on my flywheel...

Again, I have done every possible test I can think of and am now coming to people with more experience for assistance because I'm out of ideas.

All I want to know for now is... as I asked before, assuming 6 pulses coming out of the pickup coil in the distributor per dist revolution, am I looking for 3600 Hz or 7200 Hz coming out of the ignition module (and hopefully out of the TACH wire on the ignition coil)? Drawing a blank here as I can't seem to recall whether a tachometer indicates cam rotations or crankshaft, so I can figure out the rough frequency I should be seeing in the ignition system at 1200 RPM (as per the ECM)? You see, I had to replace the ignition coil last year when it died on me in traffic. So it's a year old. The backup is of unknown age and condition. They both do the same thing. I am trying to find out if the issue is either the ignition pulses going INTO the coil (the coil trigger pulses) or coming OUT of it (the pulses providing the TACH signal). The TACH is fed off of the COIL and the ECM is fed off of the MODULE. If there is a disparity between the signals going IN and OUT of the coil, that would tell me whether the coil is shot again or not in such a way it's modifying the ignition pulses going to the tach.

Is the misfire there while loading the engine (power braking)? If so either use injector shutdown on scan tool or use a good set of insulated plug wire pullers and remove 1 at a time to see which if any have the least influence to your misfire while engine is under load not just idling

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Ugh. Again, I have already done a full cylinder power balance test. This misfire is completely random and is NOT isolated to one cylinder. Disconnecting one injector at a time yields no result. Disconnecting one plug wire at a time yields no result. The engine speed drop on each isolated cylinder is identical.
I think you guys are missing the point in that this car is OBD I. There is no such animal as "injector shutdown" even on the GM TECH I. Even if there was, this engine is batch feed, so shutting down one injector kills the entire bank on that side of the engine.

Now, my entire ignition system is BRAND NEW except the wiring between the coil and the ignition module and the module and the ECM. I just put a brand new coil in it last weekend and a brand new GM module in it about an hour ago. I have added secondary grounds to the module and the coil and the body.
The entire distributor is brand new with the exception of the main body. The mainshaft is NOS and was replaced because original shaft had magnet cracked in half. The pickup coil is NOS. The module has less than 10 minutes run time. The rotor was shipped with the mainshaft. The cap has only a couple hours on it and has brass terminals.
The ignition coil is brand new as I said before. Oh, and a new symptom appeared when I first started it after I installed it last weekend... Revving the engine sometimes drops the tachometer to 0 and then back up again. Only on this coil.
The wire set is brand new.
The spark plugs have about 3 hours on them. And they all show signs of normal combustion.
The fuel injectors have about 3 hours run time on them.
Fuel flow is 130 GPH from my external fuel pump.
Fuel filter is brand new, 30 micron, 6AN. Well, not brand new, but it's less than a year old.
Compression in all 6 cylinders is around 180 PSI.

And, this car hasn't been driven in over 2 months now. And I can't really power brake it without killing my clutch disc (5-speed). And yes, I can see (via the tach) and feel the misfire while driving.

I can't really screw with it for too long while it's running at the moment as my voltage regulator in the alternator decided to take a dump again and it's not charging. And yes, right now it is unplugged since it's not doing anything anyways just to see if the misfire is due to a bad rectifier assembly inside.

Seriously, guys, I have been wrenching on this issue for 6 months or better now. I have tested, checked, retested, and rechecked EVERYTHING. The more I have either adjusted or replaced, the worse the problem has gotten, not better. For some reason, the issue seems to lie with the pickup coil in the distributor, which is brand new and tests within specs and is using all stock parts, the toothed wheel and the magnet and the reluctor. I'm going to try to get a cheaper oscilloscope and find out what the signal pattern looks like. Along with the coil output signal, from the module, that seems to be bouncing all over the place, even with a new module. Or 3 old ones. Something is definitely rotten in Denmark here. Not sure if I have the wrong module or what, but I have used the Delco D1943A in the past on the old car with no problems, so why now? With 2 of them in a row? With a fully rebuilt pickup coil assembly?

Finally got a cheap scope. Ignition module output on coil wire (and as a result, the TACH wire at the coil) is all over the place, sometimes by as much as 300Hz. I have to redo the recordings I took of the scope with labels so I know what's what so I can post to youtube or somewhere.

Scope shows perfect fuel injector wave forms on both banks of injectors.

Obtained another new GM ignition module from the dealer. This one does the same as the other one.

Finally fixed the body-to-engine block ground. Doesn't seem to have helped. Neither do the grounds I added to the coil and module.

Resistance tested all the wires on the primary ignition side. Every wire is .02 ohms. Haven't yet checked the frequency output to the ECM. We loaned the Tech I to another dealer and haven't gotten it back yet so I can't use it.

I have tried a low resistance copper wire between the coil tower and the dist cap. No effect. As a matter of fact, the engine didn't want to run with ECM controlled timing with wire installed so I took it out.

Replaced alternator yesterday. Finally charging at 14.7 volts like it should be. IDK if there is a VAC spike in it or not... Seems like even after replacing the rectifier assembly in an older one (yes, I rebuild my CS130s but I just went with a cheaper route this time as I didn't want to wait a month for the rebuild kit to show up) 3 times I still couldn't get rid of it... I even put a diode in the output line to soak it up at one point and all that did was nothing.

Misfire seems to have somewhat lessened at hot idle but still present. Tach isn't jumping as much or as high. Same as before when cold. but tach is no longer taking a nose dive when engine is revved.

Ignoring the tachometer scaling issue for now I would be interested in seeing if the ignition timing is jumping around and causing the misfires. You mentioned that you occasionally saw irregularities in ignition timing while watching the marks on the balancer.

Random misfires can be a pain in the ass sometimes.

Using a pressure transducer in the tail pipe as a synch to the misfire event, inspect the ignition timing with a scope at that moment and compare to a moment without a misfire.

I don't have a pressure transducer or the funds to get one. The ignition firing is no longer between cylinders but it has been varying by about 4* under ECM control. And yes, with it being so cold, I can see the misfire in the exhaust before it warms up... Steady exhaust stream then momentary pause (I'm talking milliseconds not like the engine momentarily stalled) then steady again.

I did notice on the scope that the initial firing spike (on the coil tower wire) is ridiculously high and jumps higher, which made me suspect the coil wire might have a fault. Would love to post a video clip of this on here but for some reason a 2.4 MB zip file is listed as being above the maximum file size of 5 MB... For some reason my phone took a 6-second clip of the recording and saved it as a GIF...

I still am concerned more with the fact that the ignition module seems to be utterly confused as to proper ignition events... AFAIK, the output frequency should NOT be bouncing up and down 300Hz with the engine running at steady idle.

What gets me is that this thing has pretty much everything, except the wiring and a couple of sensors, brand new or just about new, so it should be running like it just came out of the factory. But it's not. The Delco D1943A module I am using is the one listed in both the GM Parts and Delco catalogs for my car. For all engines (for some weird reason... I wouldn't tend to think you could use the same module on the 2.5 L4, the 2.8/3.1, and the 305 and 350).