Hi all. It's been a while since I've been here and I'm in need of some help. My Corvette fell on its face the other day. I was cruisin' at about 40mph, running great (no prior misses, etc.), when I started losing power and had some slight backfiring from the exhaust. The engine finally completely stalled and I pulled off the road. I tried starting it back up and it would actually run (stumble) at what seemed to be 75rpm, extremely slow. I called a friend and we tested for spark on a couple of plug wires and straight off the coil and both appeared fine. I had it towed home and tested fuel pressure at the rail when I got there. 43 PSI key on and while cranking. I tried the opti test described on this page LT1 F-body Tech Articles and I read voltages at the ICM but on different pins. Maybe the f-bodies are different. Doesn't sound like an opti to me, so i figured I'd ask for others opinions. Any help is appreciated. Thanks!

 

I just tried a known good coil and ICM, still no luck. I'm going to test to see if all of the injectors are firing now. Any input is still appreciated. Thanks.

 

Ok
-Fuel is ok, you have good pressure, but check the injector fues (left and right banks), they may be blown and wont fire your injectors....

-You have a good coil, Icm, opti is in question...check for spark at the plugs....unfortunately that is the only way. A

-Are you getting any codes. Low resolution from opti maybe?

-Also check for corrosion in your coil wire, you will be surprised how many people it gets.

 

Thanks for replying! I'll check the injector fuses next, and use an LED on each one to see if they are all firing.

I've already checked for spark at the coil and on a couple of plug wires and it had good spark.

No codes...


Thanks again!

 

Injector fuses are good.

How can I have spark and fuel but no boom? Could something in the opti be screwed and mess the timing up that bad? Maybe the "slotted plate" or optical plate, which ever has shifted or spun from its original position?

 

No codes hmmmm.,,,that rules out your MAP, and throttle position sensor which are critical at start-up. It would surely fire a code for these.

Good Fuel and Good Spark but no boom, then it must be timing. It could be flooded also. But it could be your opti. Which would probably throw a low resolution code.

Smash the throttle 100% and crank it. The pcm will automatically go into clear-flood mode, just lay off after it cranks if it does.

Is your throttle linkage ok?
Good Luck

 

Check your cat(s). Might want to drill a quarter size hole before one of them to see if that fixes it.

 

You've got to be kidding right?! After that then what? fill it with JB-weld? So lets review here, we can pretty much say that the opti is in fact at fault after testing everything "ICM, coil, ECM, injectors, wires, etc.." but what would cause the opti to alter the timing so bad that the car wouldn't run at all? My opti has thrown apart the HV rotor but was easily fixed with a new cap kit... has anyone ever seen the timing disk or the small drive spline shift?? The ECM is not throwing any opti codes at all.. but at the same time it makes a hell of a spark from both the coil and the plug wires. Like 95Hawk originally said, it happened very abruptly just cruising down the road.

 

Beleive it or not, I'm not kidding. But you probably never seen how a car with a clogged cat behaves, have you?

 

It doesn't sound like a clogged CAT to me. Mine plugged up on my '94, it would still idle fine, but progressively lost power starting at high rpm, then worked it's way down to low rpm over a few weeks. But you never know.....

You dont need to drill a hole in your exhaust to test it. Just unscrew the air injection tubes on your exhaust manifolds. This will relive the backpressure from the plugged cat.

I did this on my '94, and presto, car ran fine. A quick trip to the muffler shop for a new CAT, and I was back in business.

 

Hmm, great idea! I didn't even think of that. Well when my cat clogged, the car would barely idle, very low like he said. It would not rev past 1000 rpms.