anmar A

i have a 1993 z28 and it was driving great all summer, but yesterday on the way to work after almost 20 min driving on the highway doing like 80 mph, the car start hesitating and stumble, i saw the rpm going to zero then come back up like i am losing power it was weird. then on the way back home the car started fine then going on the highway after 20 min of driving started doing it again, this time it stalled twice on a red light, but started back up but kept on hesitating and stumbling until i got home. does any know what symptoms these could be? no service engine sign, i already bought a new ICM module and i will install it on Friday.

Injuneer

Scan it for codes - very easy on the 93 LT1. DTC 16, the code for loss of low resolution pulse from the Opti, which will shut the engine down, does not turn on the SES light.

anmar A

I did. no codes, i used tuner Pro RT software.

Injuneer

Probably would have been a good idea to mention that in the first post.

What does the ECM do to the IAC counts when RPM drops or it stalls?

anmar A

i haven't recorded data since this started happening, because the car runs fine when cold but it will do that after i drive it for 20 miles or so on the highway. i will get the new ICM today and i will record some data tomorrow and see.
what should I be looking for IAC count wise?

Injuneer

At normal idle, they are typically in the range of 20-40 counts. What is important is what happens when the engine RPM starts to drop. The ECM should be increasing the counts to prevent the engine from stalling. If the ECM increases the counts, but the RPM does not respond, could indicate a faulty IAC motor, or a plugged IAC passage.

anmar A

so i got my new ICM installed it, and the car still doing the same thing!! i will try to record more data on my laptop today, have a feeling is my 2 year old MSD optispark, because i checked my stored DTC and it was showing DTC 36 "lost primary crank signal"

Injuneer

DTC 36 = loss of the high resolution pulse signal from the optical cam position signal in the Opti. There is no crank sensor on the 93-95 LT1, and the crank sensor on 96/97 is only used for misfire detection.

anmar A

ok thanks for correcting me, but isnt that related to the opti? this is going to be my 3rd opti that goes out in like 4 years now, what is going on? there is a little oil leak coming out the opti seal but not much, i tried to fix it earlier this year "put a new seal on" but it is still leaking, idk if this is the reason why, I've been spending alot of money on this car since i got it!!
kinda getting too frustrated with the Lt1 and GM's stupid opti design.

moparman

Get a Delphi or AC Delco opti.

Injuneer

Yes, the optical cam position sensor is part of the Opti.

You have a 22 year old vehicle. Oil leaks are not uncommon for an engine that age. If you replaced the seal correctly, it wouldn't be leaking. Not sure how you blame that on the Opti.

What has failed on the previous Opti's? What brand have you been using to replace them?

anmar A

i did replace that seal twice and it's still leaking, the opti seal is very easy to take out and replace, so i dont see how can i put on wrong. the previous opti i used was a summit racing opti spark, then i used the MSD opti spark, it was working great all of last year and this year, i still dont know if it is the opti that it is failing, i am assuming it is because the car is throwing DTC 36, and it only happens when the car warms up, plus i feel a loss of power, the car isnt driving right any more. i do have the tunerPro RT that i can use, but i dont know what to look at to figure out if the car is losing crank signal or is it the coil or something else like a fuel pump, i dont know.
if the opti was placed right and sealed correctly, i dont think that alot of people who owns Lt1 cars would complain so much about that module. i mean the amount of work and money to replace that part is alot.

timnfxr

Are you sure the oil leak is from the opti seal in the timing cover? When you replaced the optis, did you check for leaks or replace the water pump drive seal, also in the timing cover? This may also be leaking, and is a common oil leak point, and will run down onto the opti, which is right below it.

Fatdog2

Are loosing any coolant?Could be the water pump as mentioned above,that's how my pump went out on a previous 93 Formula I had.Hope this helps.

anmar A

so i just want to update you on my car situation, so i took everything apart and got the optispark out, it seems like there is a little oil leak coming from the water pump seal "i will take care of that", but i opened the MSD opti and it looks very clean and dry, i dont know why did it fail? is MSD opti's known for failed optical sensors? it is only two years old with less than 3K miles on it.
so i am thinking of going with the LTCC setup, does anyone have an idea what kind of parts will i need, is there a place where i can buy the brackets for the coils from? and will dynaspark genIII opti work fine for this setup, any idea on the best opti to use with the LTCC setup?