1992 C4 - code 12 no start. Fuel and Spark okay

[qwiketz]

Hi guys. I've been chasing problems on this car for a while. I thought it was my opti, but ended up being the ecu solder joints. I had it rebuilt. I had already tossed in another opti (which wasn't in good shape apparently) and the car wouldn't start. I wasn't getting spark or fuel. I swapped my original opti back in and now I have spark and fuel according to a noid light. I have fuel pressure at the rail. I'm not getting a sputter or close to a start. The car cranks fine and I have code c12.

Any areas for me to check? I cranked the car for a few seconds and on cylinder 2 I saw the spark tester light flashing evenly. The noid light appeared to be flashing evenly as well. The voltages at the icm connector and opti harness seem okay. The only one I didn't test was the ac current test on the opti.

Also, the tach does not appear to be moving when cranking. The car does have an ignition box but the wiring appears to be okay and once again, I'm getting spark.

Any suggestions on stuff to check or look into?

 

[hcbph]

Just some general thoughts: to run you need air, fuel and spark in the right combination at the right time. If you have the 3 then maybe it's something like timing that's getting in the way.

 

[DonB]

I know little about the Optispark system particulars, but since you have spark, fuel (and) pressure with obviously air; Is there a possibility you are 180* off on the base timing. On all engines it'll definitely cause that kind of behavior and it is easy to have happen. The timing marks will line up but you are on the exhaust stroke instead of the compression stroke. Just a thought.

 

[qwiketz]

I know little about the Optispark system particulars, but since you have spark, fuel (and) pressure with obviously air; Is there a possibility you are 180* off on the base timing. On all engines it'll definitely cause that kind of behavior and it is easy to have happen. The timing marks will line up but you are on the exhaust stroke instead of the compression stroke. Just a thought.

A few questions. The 92-93 vette opti threads into the engine in just way; at least that's what I thought. There is the difference in splines that only point one way. Or, am I missing something? Is it common for stock rotors to come loose and spin on the splines of the opti input shaft?

 

[DonB]

A few questions. The 92-93 vette opti threads into the engine in just way; at least that's what I thought. There is the difference in splines that only point one way. Or, am I missing something? Is it common for stock rotors to come loose and spin on the splines of the opti input shaft?

Maybe another member with opti experience can help. If you are getting a 12 code and nothing else the computer is telling you there is no problem it can detect. This tells me that the electronics and sensors are functioning correctly.

Check out this article.
http://www.corvetteactioncenter.com/forums/c4-general-discussion/108450-opti-spark-testing.html

 

[qwiketz]

Here's a pic of what I'm dealing with on the back of the opti. It appears that there is only one way to get it fully seated. Perhaps I should remove and rein spect that I do have it seated properly and fully.

http://shbox.com/1/93-94_opti.jpg

The opti appears to be working since I have fuel and spark; maybe the timing is way off.

 

[DonB]

Yes, according to your pictures it appears there is only one way to install it. I'd try bumping the engine around till #1 cylinder is at TDC on compression stroke. Stick your finger in the spark plug hole and crank the engine. When it blows your finger out(and it should or this indicates a low compression/cylinder wash-down situation), you are close. Then line up the timing marks on the vibration dampener to true TDC, 0*(it's usually the biggest notch on the scale.) Then make sure the #1 wire is connected to where the Opti's rotor is pointing. Then you know you are right-on TDC. Then make sure rotation and firing order is correct.

Just a wayward thought. Is there a replaceable module in the opti? I've seen the module in regular HEI distributors spark but at the wrong time when they go haywire! Also,.... How much pressure do you have at the rail? Annnd, just for the hell of it, does your motor oil smell like gas?

Are you in Lake Forest, IL? I'm down in Oak Lawn, IL.

 

[qwiketz]

I'm actually down in lake forest, CA out west. Thanks for the suggestions. I'm going to surf the net and see what more I can find out.

 

[DonB]

OK. Good luck! Let me know what you eventually come up with. I'd be interested to know.