Car = 1994, lt1, 6 speed, 89,000 miles , No leaks oil or coolant that I see where I park in the garage (epoxi floor)

What happened = just driving down the road, 57 mph, all of a sudden the engine just turned off, I look down, then starts back up (manual transmission). Check engine light turns on, along with the service ASR. A\C also then stopped working.

I put my snap-on scanner on it and I have code 36. I believe it is opti-spark?

Now the vette cuts in and out when driving it....

Looking for Ideas what to check and or replace. Opti-spark, what components or entire assemble. Water pump since it would have to come off any ways?

This is the first problem I have ever had with the vette, I own a snap-on scanner, and the service manuals. Any insight is very much appreciated.. Thank you

 

Yep, the opti has decided to retire. Replace the opti unit, not just a cap/rotor.

 

Don't assume it's the optispark. Go through the diagnostic chart in the FSM. My car had a DTC 36 that turned out to be a bad ground because of a cracked heater hose.

Bob Thomas
40th coupe

 

I had similiar problem recently, had to replace opti. Which opti can be a controversial subject round here, I spent lots of time on actual research of that topic and not just in this site.
I agree with above post, get out manual/voltmeter and check connectors etc. If yours has lots of miles, might be time for a "major tune-up" anyway.

 

is your scanner for OBII? or can it read OBI and OBII?
i have a OBI and a OBII code reader, but niether will work on my 94.
i may need another cable or reader???

 

Code 36 is obviously high resolution pulse. But it will not kill the engine as the low resolution pulse can. High resolution is for precision timing using all the inputs to the PCM. The engine should still run.

I would first look at the ICM as your symptoms indicate it could be bad.

I would also check all pin connections on the connectors for the coil, ICM, opti and PCM. If nothing shows up I would pull and wiggle anything I could.

I suggest you check the codes with the on board diagnostics. It works very well and gives reliable information.

 

It is a snap-on scanner, yes mainly for OBD II systems. But it reads the 94 vette with the correct cards. OBD II connection on OBD I computer IIRC. Took some trial and error to get the right card but works good.

Dam I will need to brush on my the abbreviations and what they are.

How dose one check the codes with the on board diagnostics? Have any links? Sorry I not familiar with the Vette's much yet. Now put me on my Toyota Supra and I know pretty much every thing to know, LOL.

 

Check the opti's wire harness for corrosion. If that checks out, more than likely it's the opti.

 

ICM = ignition control module and 2 years ago the same thing was happening to me and that's what it was.

 

http://www.corvettephotographs.com/c4vettes/codes.htm

http://www.corvettephotographs.com/ecm.html

these might help and/or direct you elsewhere, on-board stuff is neat...

 

I had the same prob..ended up changing the opti, wires and plugs..wouldn't start..changed the icm..and that was the real prob..yes the opti was pretty worn out so it was a good move but I prolly could have gotten away with just the icm and coil..which was a 20 minute job compared to the 30 hour job for the opti and plugs, wires..the icm and coil will set you back about 150.00...the opti and stuff..about 700.00..so I would try the icm first..and don,t forget the heat sink paste...

 

I had a very similar experience with my 93. I had just purchased it in January 2011 with 19K miles on it. March of 2011 it set the SES light and threw the 36 code. Both fans were on 100% of the time. Other than that the car ran fine.

I did get the FSM, worked through the decision tree for code 36. Measured the 4V at the connector, everything was there, FSM said it must be the opti. Before I tore apart the engine I wanted to be sure, so I got an oscilloscope and looked at the high resolution encoder line. I got access to this signal by slipping in a 30AWG solid gauge wire on the back side of the inline opti connector, maintaining the connection. I clipped the scope lead on this wire and started engine. Sure enough it was flat-line, NO digital pulses. So that told me the encoder in the opti was fried. I replaced the opti (plus plugs,wires,WP, belt) and car runs fantastic.

I would highly recommend scoping out the high res pulse. If digital pulse stream signal is not there, either problem is a cable/connector or opti, most likely opti. If it is there, then it may be ECM or ground related. A scope is invaluable looking for these signals. If you don't have a scope borrow one from a geek friend or they can be had for ~$200 on EBAY. The fact you said yours is cutting out suggests you may have something else going on. Mine never cut out, just constantly threw the 36 code.

 

And if its the opti...tons of info here on EVERY aspect of it...