Injuneer

How are you testing for spark at the coil?

Susie's Z

Spark tester !

Injuneer

At the coil, or at the distributor end of the coil wire?

Susie's Z

at distributor end of coil wire !

GaryDoug

Is it an adjustable spark tester? If so, how long is the gap and have you tried reducing the gap?

Double check the ground wire at the ICM pin C with the ignition off. Should be near zero ohms. Do not use the "50 ohms" procedure.

Measure the signal at the ICM pin B while cranking. Measure in ac volts and then in dc volts (will be varying widely)). Report those values back here.

You can try unplugging the transmission, but if the 12v is at the coil, it shouldn't matter, even though it may be the original fault.

Susie's Z

it is adjustable and I tried that. ICM @ C i get 0.00 Ohms. AC to B from 2.3 to 3.7 right at the end would spike to 8.7. DC @ B 1.5 to 4.52

GaryDoug

Have you tried replacing the coil-to-Opti high voltage cable? Perhaps it is shorted.

I am running out of ideas.

Susie's Z

Yes tried that too. Was reading on another LT1 forum, it was explaining that if coil and ICM check out ohming and voltage wise, it has to be the opti. So I bit the bullet and pulled the opti. Upon dis assembly I noticed a rust stain on the plate that goes under the optical disc. It was not there when I put it on, I know because i opened it up when it came , ( i like to know how things work) and watched several reputable tutorials. When i first got it running good, the Y radiator hose sprung a pin hole leak right at the little hose and fitting (dripping right down on the opti). I'm thinking first time it blew the fuse, second time it blew the opti. So I have ordered an OEM Optical sensor and I'm going to rebuild the opti myself. I'll let you know how it turns out sensor should be here by thurs.

Susie's Z

is there any way to test the optical sensor itself ?

Injuneer

The optical sensor is the only part of the Opti that sets codes. Scan it for codes (DTC 16 and DTC 36). The codes will tell you if there are problems with either or both of the pulse signals from the sensor.

But the reason no one suggested the Opti is because if you have the correct AC voltage on the white wire from the PCM to the ICM Pin B, the PCM is receiving the low resolution pulse signal from the optical cam position sensor. If your tests are accurate, and your ICM and coil are functioning correctly, the coil to Opti high voltage wire is the only piece left.

shoebox

Where did you order an optical sensor from?

Injuneer

I missed that part. Going to be interesting if someone has found one after 22 years of them not being available.

If the 94 has the original Opti in it, going to be a challenge to rebuild it. The 93/94 units have the shutter wheel tack welded to the assembly that holds the rotor. You have to drill out the weld to remove the wheel. Realigning the wheel, without the tack weld is near impossible. As far as testing the sensor, with the harness connector on the Opti, and key on, slowly rotate the rotor and the voltage on the low res signal on pin A should switch slowly between 0V and 5V. The voltage on the high res signal on pin B should rapidly switch between 0V and 5V.

The problem with looking over an online reference like "The Optispark Dissection Page" is that it shows the 95-97 unit, that does not have the shutter wheel welded to the rotor support. It does not mention that disassembling a 93/94 unit is somewhat destructive.

GaryDoug

Easy enough:

shoebox

I knew it, I knew it!! AIP. You couldn't pay me to use anything from them. They scammed LT1 owners back in the day with their terrible optis and poor customer service, enough to bring people to the verge of a class action lawsuit. I also have speculated that they changed to using their initials instead of All Ignition Products to get away from the bad rep. I'll never forget the ire of LT1 folks everywhere. The bad rep for aftermarket optis literally started with them, IMHO.

Injuneer

But Rob.... it's so good for the Chinese economy.

I haven't heard of those guys for years. You were generous in your evaluation of their products. I thought someone had finally put them out of business.