dusterbd13

good friend of mine has a 93 corvette, lt1 6 speed. beautiful car.

he was out driving, ran flawlessly.

got home, and it died in the driveway. has not restarted since.

the original optispark died a few years ago, and was replaced with an MSD unit. new plugs, wires, water pump, etc at that time.

my guess was ignition module. replaced that. no dice. car still doesn't run.

fuel pressure is within spec.

the coil will shock the crap out of you if you touch it while cranking the car (I'm talking the lead to the coil wire. did this by accident, but it tells me the coil is getting signal to fire.)

injectors click when cranking (verified through mechanics stethoscope).

no fire at the plugs.

so, that leads me to believe its either a bad coil wire, or the rotor has gone.

any other ideas I'm missing? any tests I should run? I'm going back over there tomorrow night to double check things with my multi meter since I didn't have it last time. and reinstall the EBCM on his z06.

dizwiz24

i would highly suspect msd optispark. they do not have a good record here.

my recommndation is to search high and low for an oem ac delco (not acdelco remanufactured in china) unit and then vent it.

after venting it (with 95-96 harness) they become 100% reliable.

dusterbd13

If you suspect that the msd optispark has failed, how do we test to confirm? Don't want to just throw time and parts at this thing.

dizwiz24

yes. understood.

does the tach needle bounce around during the 150 rpm or so from cranking w/ the starter motor?

the tach gets its signL from the optispark.

this is the simplest test

93Rubie

If your coil is sparking the Opti part of the distributor is working and so is the coil. If you have NO spark at the plugs the problem is in the coil wire to the distributor, the cap or rotor, or possibly the plugs/wires but that is unlikely as they would have to fail all at once.

I would confirm the coil wire is attached to the distributor and if so the I suspect a rotor failure inside the cap. You may just need and cap and rotor the rest of the distributor from what you have said is likely fine.

dusterbd13

That was my train of thought exactly.

Will confirm tach signal, and check spark at other end of coil wire.

dizwiz24

the cap/rotor part is not what traditionally fails on the msd units. those might fail after 100+k

also the coil and spark control module usually dont fail. its usually always the optispArk - unless the optispark has been sealed up and a custom vent added. then it becomes 100% reliable. unless the vent system breaks down and water intrusion occurs.

the optical sensor is usually the issue. my test will confirm that.

dusterbd13

The tach moved a little. Spark at the Opti end of the coil wire.

So, what rlse?

TorchTarga94

Time to dig in.

SJW

If you're getting strong spark to the coil input post on the Opti, but no spark to any of the plugs, you're almost surely looking at a rotor/cap failure of some sort. The rotor may have come apart. Or spark may be following a carbon trace to ground on the cap or rotor. Possibly the centr of the rotor has burned through, allowing spark to arc over to the distributor shaft.

Live well,

SJW

dizwiz24

agreed. is it an intermittent problem?

need to take it apart and test it key on with coil wire attached to it and a single wire with a spark plug (grounded of course).

spin the shaft and see if sparks shoot out of it.

if it does then its good

also add weephole mod to waterpump while you are in there

93Rubie

Dig in, at this point no more testing is needed. You have spark at the end of the coil wire. The cap and rotor are not doing their job. Remove and inspect.