Nothing concrete to go on so let's just throw out some ideas. Look at the coil and see if there are any tell-tale white spots on the insulation indicating miss (as I call it "side firing"). Coils are considered "tune up" items.

Open the hood at night and look for a light show on any ignition component.

 

Thanks for the suggestions. The coil looks good, or as good as a coil can look I suppose. I watched the engine run for a few minutes last night and didn't see any arcing or sparks around the plugs, wires, coil, opti or anywhere for that matter.

I'm arranging to have the car scanned which will obviously narrow the scope of my issue considerably. I do appreciate all the assistance so far and I will check back in with those results for analysis and/or resolution to the trouble so that future generations may be spared this misfortune.

 

Was able to get the car scanned with a basic OBDII reader and the only code present was P1361 which was something about ignition control and/or misfire. Not sure if that's just a remnant from a few days ago when the SES came on after a particularly rough session of bogging/stalling and re-starting or if this is an indication of what's actually wrong.

 

P1361 = Igniton Control Circuit low.

Diagnostic has detected a grounded circuit for the ICM.

 

I wanted to check in and provide an update. I replaced the ICM and checked all wiring/harnesses and found nothing abnormal but my trouble persists. After clearing the P1361 it has not returned but I now have a P1351 which won't go away -- the reader listed it as misfire but I've read elsewhere that the LT1 specifies it as more ignition circuit voltage trouble. I have a new coil arriving this week and I'll replace my current coil and the coil wire at that time but I'm not really expecting any improvement from this. It's looking more and more like the opti...

 

1351 is the IC line that fires the ICM from the PCM on the white wire. 1351 specifically is an open circuit. If you don't want to ohm it out, simply run a second wire.

You can replace the coil all you want, but the 1351 has nothing to do with that.

 

That's good information, I'm going to give that a try. I really don't have any hands-on experience using a multimeter (nor do I own one) but I'm going to pick one up on the way home today and test the wiring components involved. I think I've got a handle on what to look for and where to test based off of shbox's diagrams and writeups but if there's any extra insight to be had, I'm very much open to receive it.

My concern is the fact that I'm dealing with a random/intermittent problem that only really happens when the vehicle is in motion. Is it possible to have everything test out within spec while the car is KOEO and/or cranking but have the conditions change while driving? Supposing I find something amiss with the wire from the PCM to the ICM and decide to just run a new wire... would I just be snipping the wire on both ends and splicing in a new run of the same gauge wire from point A to point B? Please excuse my ignorance.

 

The problem is more than likely the connector pins themselves. You might try bending them in such a way as to tighten the connection when they are connected. If that is the case with the pins, another wire will probably not help.

 

Ok more testing = more findings. The car died completely last night and wouldn't restart until this morning but I was able to perform some tests during that time. I'm not really sure how to interpret these results so hopefully you experts will be able to shed some light.

I verified I had good ground and good DC voltage on the proper pins at the ICM connector. When checking AC voltage on the connector pin for the white PCM wire at the ICM connector (disconnected from the module) I got different results at different times. Mostly I got 0.050V while cranking the engine so I went up to the PCM and pierced the white line in the 'black' section of the PCM and tested there. My result there was about 2V so I figured hey, there's a short, I can fix this! The problem became as I continued to test I found that I would intermittently get the same low voltage as I was getting at the ICM connector. Then I would get solid voltage again. I went back and rechecked at the ICM again and found that I was randomly getting good and low voltages there as well.

What can I test now and what should I be looking for? Could this be a PCM problem? Would the opti's signals to the PCM cause a variation in voltage as it's passed down to the ICM? I'm ready to fix this once and for all -- I'm getting pretty tired of ending up stranded places or having the car die in the middle of the road (several times) every day.

Also, I uploaded a video of how my car is behaving to YouTube so you guys can feel my pain or get a better idea of what symptoms I am dealing with.

 

Any ideas? Going to order a new optispark tomorrow and as much as I dread replacing it and fear for the possibility that this might not clear the trouble it's all I have to go on. Thanks in advance for any other suggestions.

 

I don't recommend it. Stick with where the problem is. If you had an issue with the opti, it would be showing a code for it.

Another opti based on what you have told us so far, is a waste of time.

 

Well that's a bit of a relief to hold off on that. Still no other codes beyond the persistent 1351 but I really don't know what to check to narrow the scope down. Is it possible to test anything on the opti harness other than visual? Anything I can test on the input to the PCM? If the intermittent good/low voltage is happening right out of the PCM there seems to be a pretty finite range of things to investigate I just don't know what to do with them.

In researching this I've found a number of other folks on various forums who have had the exact same trouble as I have but there were no resolutions posted -- most were from several years ago but maybe I can try emailing those posters and see if can recall anything about their fix. I'll make sure once I'm confirmed fixed that I post the solution.

 

I recommend going from the pin of the PCM with a separate (home made) wire to the ICM. If it then has a problem, you need to determine if the ICM is causing the problem.

Now here's the deal. The ICM could have in input problem. However chances are if the wire has the same signal pattern on it with the ICM plugged in as it does when it is unplugged, then the ICM isn't the problem. However, some lines require a load for them to operate properly so be careful here.

At that point you would think the PCM is defective however, you don't know if the PCM is not seeing an input on another connector and simply doing what it's supposed to. But, you know if the opti inputs aren't being seen, the PCM should throw a code.

Hope that gets you started in a good direction.

 

I promised an update with closure and here it is. I did complete testing on the ICM and related wiring and found no faults but was able to verify the problem was present on the harness right out of the opti. Replaced that harness to no effect so I went ahead and replaced the opti last Thursday. The swap wasn't nearly as painful or drawn out as I remembered it to be the last time I did it on my previous SS eight or nine years ago which was nice.

Spent the weekend putting in hours behind the wheel and miles on the clock and all troubles are completely gone. No hesitation at any RPM, starts up the instant the key turns each time and doesn't skip a beat.

I disassembled my old opti (looks to be the original) and found a handful of problems with the cap and rotor. The rotor was dragging on the casing in one section and there seemed to be evidence of arcing inside the cap. Wish I would have swapped it out earlier and spared myself weeks of downtime but it's a relief to know that the rest of the system is now new or thoroughly vetted.

TL;DR - optispark was bad, I replaced it.