My 94 LT1 just died on my lunch break. I was at a light in gear at idle when the rpm's started surging to 1200. I took it out of drive, idled up to 1200. Put it back in drive, and it died. Crank no fire.

Pushed it to the side. Crank no fire. Hmm. Checked all the fuses. All good. Pulled the coil wire out of the Opti. Cranked, had lots of spark. Coil is good. Plugged it back in, pulled #2 wire out. Cranked, had lots of spark. Plugged it back in.

Shouldn't be the coil or opti, right?

Unplugged my firewall mounted fuel pump relay. Bypassed it, pump turned on. Heard some different blurbing from the FPR. Hmm. Cranked with the relay manually bypassed, no start. Schrader valve didn't seem like it was at full pressure. The little "pffft" of fuel you get didn't seem very peppy. Hmm. I just replaced the pulse accumulator from between the fuel pump and pickup tube this spring. Shouldn't be that again.

When my gf picks me up after work, I'm going to check the fuel pressure as well as check voltage everywhere. I didn't have any tools with me so thats the best I could do.

Is there a crank position sensor anywhere else besides the opti? I'm pretty confident that its fuel related. Thanks guys.

 

Fuel pressure seems to be the problem here if your getting spark to the plugs as you said you are, you could always bring some starter fluid etc to help test if its fuel but be careful if you try to do it that way.

Hook up a gauge too it and you'll probably find your problem, the crank position sensor being bad or even broke/unplugged would not cause the car to not start.

 

Plenty of fuel?

 

I'll get on it and let you guys know what I find. I'm sure its something simple. Is there a sensor somewhere that would kill it like that? Maf would make it run bad. Opti kills it for sure, but anything else?

 

Loss of low res pulse from the Opti shuts down the fuel pump and injectors. Bypassing the fuel pump relay would provide fuel, but the injectors would still not deliver it.

The 96/97 engines have a crank sensor, but its only there to detect misfires. The PCM still runs off the Opti low res pulse pattern.

Have you scanned it? Loss of low res pulse will set DTC 16 (OBD-I, what year is your LT1 engine????).

I believe I've also read that DTC 42, short/ground in the ignition control circuit will also shut down the fuel system, to prevent the unburned fuel from washing down the cylinder walls. But you say you have spark, so it doesn't sound like that's the problem.

 

ICM will kill your car when it gets hot, runs fine when cold. But like Fred said, since you get spark it is most likely fuel related. A fuel pressure test should tell whats up

 

i was thinking IAT Sensor

 

The IC Module translates the small pulse signal from the PCM to a signal that causes the coil to fire. A faulty ICM can kill the ignition. ICM has nothing to do with telling the PCM anything... its not a sensor, its an actuator.

 

This is a 94 LT1 that I put in my 89 chassis. I haven't had any problems with it yet other than the fuel tank. I haven't scanned anything yet, but I can push the car 6 blocks to a friends garage. He has a scanner there. I also brought my fuel pressure gauge and a multimeter. Hopefully I can find out what it isn't after work today.

 

Well dudes, I went to push the car to my buddies house. The damn thing started right up! So I'm going to get it home and try to scan it. Hopefully the PCM caught the culprit and I can address the problem. Grrrr....

 

I got the fuel pressure checked. Nailed 50psi on, 46 on crank. So that shouldn't be the problem.

But wouldn't you know it. I go to drive the car home since it started the last time I tried. It started right up so off I went. It died once and restarted, then I got half way home and stopped for some gas. Started it back up and the car was miss-firing and DIESELING! Sounded like it was running on half the cylinders and then would diesel to a stop, dumping gas out the intake! It looked really weird. Plus my gf said the car was backfiring, shooting flames a couple feet long out the tail pipes. Needless to say, I had to tow it the rest of the way home.

So now I'm thinking that my problem is Opti-spark related. Damn cars. I'm guessing that could be the reason it instantly dies. Plus if the Opti went out and was giving the computer false spark info, it could be pulling/advancing so much timing that it wouldn't start right? That could give me my spark no start condition? Now that its home I'm going to tear into it.

 

Alright. I got the laptop running and I pulled the codes.

Code 16 - Lo Res Failure
Code 36 - Hi Res Failure
Code 42 - EST Grounded

It will consistently run when its cold. As soon as it heats up it dies and won't start again. I data-logged the last run and all the sensors seemed to be working. But when the problem occurred, the engine was at 180*F and the spark advance was jumping EVERYWHERE! It hit 41 degree's at idle!

Think its optipark related? Those things are expensive.

I've added spacers on the control module so it sets about a 1/4" off of the head. Do you think it could be that? Its not getting warm at all. Even after it starts acting up.

I just did the http://shbox.com/1/4th_gen_tech2.html#opti_test . I have voltage out of the ICM but the signal in is not there. Hmm. Sounds more like the Opti?

 

Since you have the two key codes for the Opti optical sensor (DTC 16 and DTC 36) its pretty certain that the problem is related to the Opti. DTC 42 is for the IC Module, but if you look at the diagnostic logic chart, is can be set bacause of problems with the Opti pulse signals. Before you jump to any conclusions, check the connectors on both ends of the Opti harness for corrosion or damaged pins.

 

The wires that I have don't match the 95 wires for the opti. I'll look at them anyway to make sure. The intermediate plug is the one on the passenger side of the intake manifold right by the injectors, right?

 

I don't know if anyone else has seen this, but its a good write-up about how to take it apart.

http://corvetteactioncenter.com/tech/c4/optispark.html