anyone know if the 1995 corvette should generate a PCM Error code (such as DTC 16, 41 or 42) if the ICM or Ignition Coil is bad ???  My 95 will crank but not start - there is no spark from the ignition coil to the optispark.  I have run the diagnostic checks from the service manual and it indicates one of these two components are bad.  But before I replace (since I cannot return the parts) I am curious why I would not have one of the above PCM error codes.  All those codes relate to ignition or low voltage.

Not having a trouble code is common...it has to "see" a specific problem, for a specific amount of time, to set a code.
I'd say yer Opti-Spark is sparked out...

The ICM and the coil are one unit...if ya replace one, the other comes along for the ride!

The Opti-Spark sux...it's usually best to just replace the whole dang thing, and be done with it. The ones you can buy now have all the upgraded stuff in them, so they survive much better.
Stingrayjim had/has a hook-up on them, I think, as far as a good source to get them from.

One thing I might add is to check your water pump while your there. It is very common for the water pump to begin leaking and cause the distributer to get wet and fail.

The distributer is also a booger to remove. Good Luck Kerry!

The water pump and optispark were new with the engine rebuild 10 months ago and since then, the engine has less than 500 miles.  If the optispark was gone, I should still have a spark from the coil into the optispark.....Right??

What th heck d'ya mean?

If there is an issue within the distributor(the opti-spark unit), the coil will not fire at all, depending on the failure mode. The optical wheel inside the distributor has to "trip", or signal the the PCM to fire the coil . Then the PCM signals the ICM(ignition control module) thru the EST(electronic spark control) by grounding the primary circuit that supplies the voltage to the coil. This collapses the coil field, which causes the coil to sparkle.
If I am a-reading you correctly, yer coil ain't firin, right?
Since the opti-spark was just recently replaced(which don't mean diddly anyway), how about the ICM/coil assy? Was it replaced at the same time?
I'd want to check and see if the PCM was grounding the circuit for the ICM, and if it is, then you know the opti is working, and the problem is most likely the ICM/coil.

If you have a test light, try this...
At the ICM connector, you should have a white wire, a white/black stripe wire, a pink/black stripe wire, and a solid black wire. The solid black is the ground for the module, so it should be grounded on the engine block.
The wire we want to check is the solid white wire. Remove the coil wire from the distributor, and place it close to something that will be a ground, like the block, or a bolt on the water pump. With the key "On", and your test light connected to a good ground, probe the white wire quickly...just a touch and release. IF the ICM is good, the coil should fire as you touch/release the test light to the white wire. If it does not, do it a few more times, just to be sure. If ya really want to be sure, grab the coil wire with your hand...you'll KNOW if the coil is firing...
If the coil does fire like that, then the problem is gonna be in the opti=spark unit, or the PCM. OR...the dang ground wire. Remember, it's STILL a Corvette, and grounds are important...

If you have a good voltmeter/digital multi-meter, you can monitor the white wire for a ground from the PCM while cranking the engine. Just set the meter for DC volts, and connect it to the white wire, and crank the engine. The meter should fluctuate from high to low voltage if the PCM is grounding the circuit as it should.

Did this just happen all of a sudden, or did it start runnin like crap, and then die?

another thought just floated into me haid...the tach filter could cause a no-spark, too, if it was grounded out...might see if you can unplug that, and give it a try...


oh yeah...one more thing....it's prolly a silly question, but has ya checked the fuses? A blown INJ fuse would also dis-able the ignition system...Adams' Apple2008-08-27 06:41:32

Well, no loose wires, forced the ICM to ground with the good old paper clip trick .... and no spark ,  test light indicated a good ground on the ICM pigtail , also have a good ohm test of the wire from the PCM to the ICM .....The coil metal casing has rust on it and Joel says thats a good indication the coil has started to magnetize which prevents it from storing a charge ...... so, off to the parts store to get a new ICM and Coil $$$$ (well, not really, going to cheat and have my son get it from the Hummer dealer where he works....should save us a few coins at dealer cost ).  Will get the new parts in on the weekend and let y'all know how it works out.
Now while I wait, time to move over to the weatherstripping on the C3 back window.....then back to finishing the C4 interior.....always something

 I'd keep in mind, the coil isn't going to fire if the opti IS NOT getting a signal to the ECM, which in turn signals the ICM to fire.

Kerry's car isn't setting any codes, tho...it just won't fire. The "scratch test" showed the ICM/Coil isn't firing, pretty much eliminating the Opti as the source of the problem. IF the coil was firing during the scratch test, then we'd be looking at a PCM, wiring, or Opti issue. He tested the wire from the PCM to the ICM/coil already, and it was OK.
Opti issues will normally set codes, but a bad coil won't, in most cases, as the PCM doesn't monitor whether or not the plugs are firing. Adams' Apple2008-08-30 14:20:36

 I'll file that away for the future too Joel. That's why I enjoy reading your posts.  

During Kerry's wait on the ICM module for kicks and giggles I would be taking each grounding points loose and inspecting, cleaning and replacing them.There are many and they should be better named as corrosion points rather than grounding points.

My last C4 opti / codes issues were like a witch hunt chasing through the codes / firing issues.
Each time I would clean some of the grounded areas it seemed to get better. (and I believe it was)

I finally traced the issue to an after-market security system that had been installed under the dash. I had not noticed it until on day I just happened to notice the light on the top of the dash was slightly different than others I had seen..... What if...? I disconnected it and found everything to be in working order afterwards. (then and now) Sooo, Bubba had struck in his quite undetected manner. Although I believe that it was no fault of his own that the after-market security system had died.

But what I did find that most likely had prompted the change in system I believe was the drivers door lock harness had been severed by the window track coming loose. Once I repaired the harness everything was back to normal working OEM condition. (OEM security system included)

Becuase in reality what I thought was an ECM then BCM problem was really something relative instead. I had a door lock keyfob problem that I had never considered to be relative.... but I was WRONG!

Moral of this story..... Every Freakin Thing in these cars is connected electronically to each other. Sooo if you may have to hunt deeper that the obvious to find the root cause. (Hence the saying "Thingz are not always as they seem!")

Hang in there Kerry my friend I lit a candle and placed it on my Corvette Alter for you my friend!