Monday morning I went to drive the car to work and it would just crank over and not run. When I came home from work in the afternoon I tried it again with the same results. I checked the ECM & the CCM for codes and got none. I checked for fuel pressure and it was at 40psi. I checked for spark at the coil and had plenty. I checked for injector pulse and tha was fine. I started to notice that the engine would try to run backward if I didn't turn the key to the off position after cranking it a few times. Out of desperation I condemed the optispark and ordered a new MSD unit from Summit Racing. It came in yesterday and I installed it. I test fired the car after installing just the new opti and it started right up ! I proceded to struggle putting the rest of the stuff back on the front of the engine and filled the cooling system. I went to start it up and now it is acting like it did before . I checked to see if I pinched a wire or something stupid like that and found no reason for the change.

The engine acts like the timing is severly retarded. I also don't hear the "spark knock" sound that I usually hear when a LT1 is cranking over.

Anybody have any suggestions?

 

[QUOTE
I checked the ECM & the CCM for codes and got none.
I checked for fuel pressure and it was at 40psi.
I checked for spark at the coil and had plenty.
I checked for injector pulse and that was fine...
I test fired the car after installing the new opti and it started right up ! [/QUOTE]

Um, you couldn't have come up with an easier problem? You have fuel, ignition and cranking. The only thing I question is how did you confirm the injector "pulse width" without running the engine. Did you put a "noid" light on the injectors while cranking? Did you check the fuel pressure while cranking?

Larry

 

If it were an easy problem even I could have figured it out without help.

I checked the injector "pulse width" by putting one end of a 12 volt test light in line to each of the connectors on one of the wire connectors after disconnecting it from the injector and watching the light as I cranked it over.

Fuel pressure was 4o psi while cranking.

 

Why didn't you check the timing with a timing light while cranking? Your symptoms indicate too early spark.

 

VATS, do you have a spare key?
Try that, it was the problem w/mine.

 

I believe if the problem was in the VATS system, it would not even crank over. VATS also shuts off the injector pulses and I DO have those.

Thanks for the suggestion!!

 

Correct.. VATS=No cranky...


I'm thinking you may have broken a tooth off of the timing gear.. how many miles does you LT1 have?also might want to check your valves.. have you recently installed new rockers or otherwise played with the valve lash?

if you have fuel and spark confirmed in the cyl.. then 1 of two things most likely are wrong..

1. timing
2. compression


you might want to do a compression test of the cyls and a leak down test as well..

my .$02

 

UPDATE!!!!!!

Last Friday I came home and started to go thru the check out procedure in the service manual for a "crank but no start condition". Half way thru the procedure the damn car started right up!!!!!
Not being the type who trusts a "self-healing" car problem I spent the rest of the weekend starting the car EVERY chance I got. I must have started it 50 times and it ran beautiful. I still wasn't brave enough to dive it though.

Yesterday (Monday) afternoon I noticed the brakes on my pick up truck were starting to make a grinding sound so I pulled it apart and sure enough the inboard pads were shot and it took out one rotor. I had test run the 93 earlier and decided to run to the parts store with it. YUP!!! It died in the parking lot of the parts store . I had it flatbedded home and I put it in the garage and closed the door .

Tonight I had a friend of mine and a buddy of his that is a GM Tech come over with his "Tech-1" scanner and we went thru the diagonastics on the car together. NOTHING showed up again. I still was getting spark from the coil, a pulse for the injectors and PLENTY of fuel pressure.
The Tech said that sometimes he just HAS to try swapping parts to figure out what is wrong. Luckly my wife's car was sitting in the garage and she was gone for the evening so we started to try on some parts. The first was the spark control module. No change. Next was the ECM. No change, THANK HEAVENS!!! Last but not least was the Ign. Coil/Module assm. BINGO!!!!!!!! The car started right up. I tried my old one on her 93 and all I get was crank, crank, crank. I ordered a new module and coil from Napa and it will be in tomorrow afternoon.

The GM Tech is building a Cobra Kit Car with a stroked small block Chevy in it so I know I will have a chance to help him out in the future to return the favor.