matty b

Hey, I have a very very odd issue. 93 Vette LT1, the problem is that the car died all of a sudden while driving and wont start since.

I had no spark or injector pulse so I scanned for codes and got a code that got me to the ICM which ended up being bad. I changed that out and retested only to have the car still not start. I now have spark on every plug and I noid lighted every injector. They all spark or occilate. I pulled the plugs and they are wet with fuel. Did a cold compression test (cause I obviously cant get it hot) and compression is ~190 for all cylinders. Fuel pressure static is 42 psi and stays up while cranking.

I installed new NGK plugs, jumpered the fuel pump relay to make sure its not shutting off during crank mode, verified no blown fuses. I dont have any codes and its not exhibiting anything that would be a VATS problem.

At this point Im totally stumped. I cant for the life of me figure out why the hell the car would just die and once it has spark and fuel not fire off or even try to catch. Im talking this thing doesnt even backfire just cranks over.

I know Optisparks suck but given the fact that Im getting spark and injector pulse Id be hard pressed to fault it. I was hoping maybe this is some known issue I dont know about? I have triple checked all the likely possibilties and still nothing.

Any Ideas????

ss.slp.ls1

iTrader: (36)

Interesting...you got me man.
Is it possible the spark is weak? Maybe throw a new coil at it and see if anything changes.

SPRAYED Z

iTrader: (4)

id say spark is weak too and the coil is at fault or the rotor in the opti fell off and its still arching just not correctly

ss.slp.ls1

iTrader: (36)

I was thinking the latter as well, but if that was the case, it usually would backfire and diesel pretty crazy. But never rule anything out.

matty b

its getting a nice blue spark. Im using a spark plug and grounding the threads to check spark. Also the spark is arcing along with the noid light.

Im at a loss myself. I consider myself a pretty compentant diagnostic tech and I have never EVER had a situation where I had spark and fuel and not even kickback or popping out the intake. The owner (my customer) just said it died in the middle of the street while in treaffic with no bang or bad noises and thats all she wrote.

Ive tried even spraying carb spray in the TB hoping to see if it would light it off. I figured this would be timing related but given the fact that I cant adjust it or even check it on this motor Im running around in circles more or less. They are short on cash and dont really wanna go much further in diagnostics so I probably wont be taking off the cover of the optispark as its a PITA on the vettes. Im curious to see if there is some issue in there though like a rotor thats broken and twisted up or something?? (just a guess)

It acts like timing is off by 90 deg considering it cranks fine but no popping. 180 out and you have backfires and such and a plug off it will kick back while crank ect. This just spins along like nothings wrong. Hell even the computer thinks its timed right and says its requesting 14 deg during crank, but I dunno. I wish Id figure it out but chances are the cash wont be there for to to get that far.

Speedy

Take a look at this thread:

https://ls1tech.com/forums/lt1-lt4-m...-no-start.html

I can tell you from experience that funny things happen with LT1 coils. You can try taking the coil off, cleaning it and reinstalling it just for kicks to see what happens. It might start. I tested the coil with a spark tester, then the plugs. But it wasn't until I used a real volt measured tester on the spark plug wires that I realized the current was weak running to the plug. It's very deceptive on these cars.

Hook your tester up between the coil and the opti and check the brightness of it, then move to the plugs and compare the brightness. If plug wire flashes significantly weaker you can be sure it is the coil. Plugs will not reveal this problem to the naked eye in my experience.

buckner163

Also try the clear flood mode. Fully depress the gas pedal while cranking it.

cgslow77

iTrader: (2)

this might sound doumb but make sure its getting air... you can have fuel and spark all day but it wont start with out air... if the filter is cloged or tb is.

matty b

pulled the intake hose to spray carb spray in..and I did leave the AIT plugged in. I also have cranked it with the pedal depressed thinking it might have been flooded, no go.

This is probably one of the strangest problems Ive ever encountered. The more I think about it I still want to look at the Optispark but the customer doesnt want to spend more cash for me to do that.

Im left with two possibilites. Either something happened to the Optispark or something happened to the timing chain. Having fuel, spark, air and compression should make some type of boom (even a backfire or pop). Beyond that something happened to that motor I have no idea about.

Thanks for the suggestions, believe me I covered all the bases and it sounds like I didnt miss anything tricky relating to an LT1. Im sure its something totally stupid and if they were willing to spend another hundred bucks Im sure it has to do with the optispark but they dont wanna spend it and I dont work for free.

Thanks guys, I hope I figure out this mystery even if its them calling me lol

ss.slp.ls1

iTrader: (36)

What does a coil cost? 30 bucks? Try a new one.