Need some tech help from you LT1 gurus

[BuickMike]

Here's the story and its a long one.

My buddy has a '97 Z28 and it died on him last week. He was getting on it and the car backfired and died. He got it towed home and found out that he had no spark. It turns out that his rotor broke. He replaced the distributor cap and rotor and the damn thing still wouldn't start. He still had no spark. I checked the plug going into the ignition coil for +12V and a pulse on the ground side and it was fine. He got a new coil and now we have a good spark all the way to the plugs, but it still won't start. It doesn't even try to fire. We charged up the battery to make sure it had good voltage and also checked to make sure the fuel pressure is good. I then pulled a plug off of an injector and tested for voltage. With the ignition on I get +12V and 12V ground. Cranking the motor reduces the voltage across the plug to 9V. This is really wierd because on other cars that I have tested the ground side of the connector stays at 0V unless cranked and that's when it pulses. If I use a voltage meter it usually shows 2 to 3 volts when cranking.

Could this be caused by him screwing up the opti-spark, of is the injector harness grounded out somewhere??? And yes, we checked all the fuses.

Thanks for any help,
Mike

 

[RBE17]

Is the Opti on correctly? That dowel pin in the cam will fit in the recessed holes for the cam bolts. I know more than one person that has gotten them on incorrectly. In some cases the car runs, but not well. Other cases, it doesn't run. How about the opti harness? Good luck, this is one I haven't heard.

Later,


Steve.

 

[BuickMike]

My best guess is that he put in in wrong. The injector harness test is what threw me off.

 

[Adrian87]

Yeah, sorry but the Opti on these things is a real bitch..I'd recommend finding an intelligent local that has a LT1 car as his personal ride that likes to mod it...anyone that's had one for a while has replaced the Opti..let him give you the pointers..just my idea though
(I had a nice stock sorta 95 6 speed TA that ran 8.30@84 mph on street tires) Damn I miss that car...

 

[CrawlinGN]

Did he replace just the rotor or the whole unit? I have replaced mine on the Z with an chain store unit and it FAILED in 500 miles. If he didn't replace the whole unit it is possible that the optical sensor is bad or the degree wheel was put back in incorrectly. I know of a GM dealer where you can get a whole complete gm unit (vented 95-97) for less than 300.00 to your door. Make sure that he got the dowel pin on the cam inserted in to the opti correctly so that there isn't any play. Let me know if I can help you any more with any questions.

EDIT : Doh you are right I was so used to getting parts for the 93 I said unvented. Thanks for the heads up.

 

[RBE17]

Some interesting points have been brought up. If your friend continues to have problems, have him pull the opti and check for the correct installation. If it was correct, I'd call Dal at Van Devere Olds and order a complete unit. The last time I bought one it was $260.

BTW, '95-'97 LT1s had the vented opti. Probably just a typo, but I wanted to clarify.

Later,


Steve.

 

[BuickMike]

He bought the new cap and rotor from Autozone. I can't remember if he got a new opti or not. My guess is that either the thing is dead or that he put it in wrong. Thanks for all the advise.

 

[Mease Performance]

distributor

Mike, purchase a new opti spark....my best reccomendation to him... buy ONLY NEW AC delco stock no aftermarket sources!!!

Does it throw any codes like a code 16 when cranking? a code 16 is a low resolution pulse from dist to the ECM, if it does not have this signal the car will not fire, if you have a high resolution pulse, but no low resolution pulse, the car will not run still.....you need the low res signal to get it fired, then the ECM takes over and uses the high res pulse to control SFI, and other features such as ESC and timing...

check the codes, if you get a low res or high res code, replace the opti, could also be the cam issue, although if the engine is stock ( no cam work) its kinda hard to mess up aligning the dowl pin since its the straight slot on the distributor drive...

Good luck!

 

[Mease Performance]

also, hehe

if he fractured a rotor, make sure the vacuum lines are correctly hooked up to the manifold, and the other one hooked to the intake system (intake bellow-vent line)

IF THE CAR HAS A SUPERCHARGER MAKE SURE YOU HAVE THE CHECK VALVES IN THE LINE GOING TO THE INTAKE (actually even if NA check them anyways) we literally BLEW an optispark to pieces here on my own car by not installing these check valves in this line (these distributors arent made to operate on 18psi )

 

[spudmanmike]

I really don't know what could of happened, esp when the car was actually running. If he went probing around with the multimeter, i just hope it didnt do something to the PCM. That piece is not too forgiving (trust me )

 

[CrawlinGN]

It is the opti, if he baought a cap and rotor kit he did not replace the optical sensor in it is what causes it to fail. Believe me and tons of other lt1 owners, get one from a dealer and be done with it.

 

[BuickMike]

Thanks for all of the replies. He's going to pull it back apart and see what's wrong with the optispark. He cranked it again and pulled out a a spark plug and it had gas on it. So, the thing has spark and fuel, but refuses to even try to fire. Wierd...