mazdaverx7

I've had ignition issues with my 94 6 speed since day one. I have replaced the opti once, and installed a new coil, and after today, a third ICM. The engine stalled the other day when accelerating and when being flat towed home some 30 minutes later, the engine started and ran fine the rest of the day. Yesterday the engine would not start and I had no spark from the coil. I check this first as it sends the spark to the opti. Much easier to check and replace if need be. So, today I replaced the ICM as I had done last year around this time and the engine still won't start. I check for spark output from the coil and still no spark. I replace the coil with a good unit and still no spark. Where do I go next? ECU?

mazdaverx7

I checked all of the fuses, even the fuse block in the engine bay. All are good. I then checked for spark at one of the plugs by pulling a plug wire and inserting a spark plug into the wire and grounding it and then cranking the engine. No spark to the plugs either. Which I figured as there is no output spark from the coil. I guess its possible that I got a bad ICM, but somewhat unlikely.

Bandit's C4

Have a FSM handy? [Book #2 - pages 6E3-C4-4 thru 6E3-C4-9]
Any codes?
See you replaced a few modules and components... how old are the wires?

mazdaverx7

I do not have an FSM. The plugs and wires were installed two years ago along with the opti.

When I connect a scanner to the diagnostic port it says that it can't connect to the ECU. Been that way for two years.

kimmer

This happen to me a while back and it ended up being one of the plug in connectors to the coil.

mazdaverx7

What was specifically wrong with the connector? They appear to be ok, but maybe I'm overlooking something. I'm up for trying any avenue of approach at this point.

kimmer

Some kind of interior break, was not getting the volts it needed. You can try using some jumper and bypass the plug. Check you volts coming from the connector.

Klondike

This is my first attempt to upload a picture or diagram so I hope it isn't jibberish!
This says 95 F-Body but it's laid out nicely for clarity and I think the wire colors are the same. I'd check for Positive voltage at the Coil connections A & B with the ignition on. I believe that the computer applies ground to the B terminal on the ICM when it gets the signal from the opti, and then the ICM applies ground to the A connector of the coil to fire it. All those connectors have fairly small wires to the terminals inside those plugs and maybe one of them has broken wires inside the connector. You just about need to check for voltages with the Ign. ON or check continuity of the wires in the connectors by OHM-ing them from one end to the other.Sounds like you have an open wire somewhere in that bunch.

mazdaverx7

Thank you VERY much for the diagram. I'm wondering if something is wrong with the opti unit and its not sending the signal to the ICM to fire the coil. Looks like I have some work to do with my multi meter.

mazdaverx7

I have a new Opti Spark unit in hand as I believe my current unit has failed. I think the ICM is not seeing a crank signal from the Opti and thus not telling the coil to fire. I have all of the parts to do the job and I will probably tackle it tomorrow.

pcolt94

The 94 is a ODB1 system with a OBD2 connector. If you are using a current scanner for 96 and up cars it will not work on the 94 vette. You need a scanner that can do OBD1 with the special connector adaptor to interface between the car and the scanner. Or, you need to have a Tech1 which is a dealer scanner for that vintage car.

But forget scanners, the on board diagnostics on the car will pull any code a scanner can for the engine plus the other modules also. Buy a FSM or get documentation on how to invoke the cars diagnostic abilities. It's a great tool that works excellent.

If you have a opti in your hand, you can just unplug the connector and swing the connector out and connect to the new opti. Turn the key ON and spin the opti with the small shaft. You should hear spark off the coil and injectors clicking. If this works, it would verify the old opti is bad.

Cliff Harris

Go here to find out how to retrieve the error codes from your PCM:

http://corvettephotographs.com/c4vettes/codes.htm
http://forums.corvetteforum.com/c4-t...n-96-cars.html

The error code meanings are listed here:

http://forums.corvetteforum.com/1576116036-post35.html

mazdaverx7

Thank you guys for the diagnostic answers. I'll head out to the garage a little later today and see what I can figure out.

TorchTarga94

Any word?

mazdaverx7

Haven't had time to do this until today. Heading down there now to get started.

mazdaverx7

Good news. I replaced the Opti Spark tonight after confirming that it was faulty and the engine runs great once again. Took the car for a drive and it ran perfectly!

pcolt94's advice to spin the new Opti after plugging it in without bolting it n the car brought spark right back. This confirmed that the current Opti was bad. Glad I bought one with a lifetime warranty!

TorchTarga94

Good to hear! I did the same today as well and she is back on the road. For now atleast....

pcolt94

Excellent! Sounds like you knocked off that opti job pretty quick.

mazdaverx7

Thanks! It took me about four hours from start to finish. Most time consuming thing was scraping the old water pump gaskets off of the block. Seems to be running great as of now. Was idling oddly when I first stared the engine. After I let it warm up and topped off the coolant, I drove the car and its running perfectly fine.

Klondike

The engineer that placed the Optispark where it is, must not have ever worked on his own cars! It ain't a job for the shy-with-tools crowd, but it is rewarding when you have done one successfully!