hello i recently rebuilt my lt1 in my 94 z28 camaro a/t. I went a stage up on my cam and used a msd cap and rotor along with an underdrive pully. The car started up and ran fine. The charging system wouldnt keep up with the underdrive pully unless i was driving but the car ran great. After a day of driving it started to bog out a little bit when i would accelerate and began to backfire out the exhaust once in awhile. When i was just sitting and idling i revved it up and it backfired a 2 foot flame out the exhaust. So i parked it deciding to change the underdrive pully out for just the harmonic balanacer. When i went to start the car up it cranked over and when i released the key it backfired out the throttlebody and the motor turned over backwards! Every time i tried starting it the same thing happened. I crank the motor over it doesnt start, let off the key then it sputters and backfires out the intake and turns over backwards for a few seconds. I checked and have good spark at the spark plugs which are new as well as the plug wires of course. If any one has any idea of what could be happening i would be most appreciative. thank you.

 

I'd say, since it ran, then messed up, that the opti crapped out, all your symptoms are ignition timing related

 

check ignition and valve lash

 

im gonna get my icm tested i think it might be that

 

Check the coil and coil wire. By that I mean watch the coil case at night in the dark while someone tries to start it. Otherwise pull the coil wire off at both ends and look for corrosion.

 

check valves to mine were over tightened but wasn't my only problem, also the opti that was on it was off time, hard to explain but the opti set for 6 tdc on the new and old opti had the rotor in 2 different places

 

ok i replaced my distributor with a new rebuilt delphi and i bought a brand new ignition coil and icm along with a new ecm/pcm because my noid light wouldnt flash when i cranked the motor over. I have like 35 psi for fuel pressure even though it should be 40 to 47. I guess even with 20 psi it would run. But none the less it turns over and once in awhile it will start for like 2 ta 3 seconds! My obd 1 wont flash codes on the instrument panel and when it was hooked up to a scanner it said computer not responding burnt fuse. There are no burnt fuses! The motor has all new msd plug wires and ngk spark plugs. Is there any way my timing is off? I thought that there is no timing involved with opti spark. The opti is seated correctly, the spline is in it and the sprocket......i did use a msd cap and rotor assembly on it though so it would be vented with vaccuum instead of the 3 holes. could the map sensor being bad prevent it from starting or staying running when it does start? Do i need to do anything to a new rebuilt computer after i install it to get it to work properly? The originial radio is gone so there is no anti theft there. I dont know where the theft deterant module is located but i do know that the orange tube coming down the steering column with the 2 small wires in it are for it and that has been cut. There use to be a viper alarms system in it but i removed that when the car was still running before the rebuild. Please some one give me an idea to try that i havent thought of yet!!!!!!!!!arghhhh!!!!!!!!!

 

94 and later cars require a scanner to get the codes...you can't flash them.

Do you have spark?

Do you have compression?

The antitheft that affects the car is not housed in the radio....do you have an illy imaged or flashing security light on the instrument panel?


The best thing to do is start diagnosing the basics...

 

Dam no outcome of what his problem was...? It is exactly what mine is doing. I have replaced dam near EVERYTHING on this truck, and it still does just what he is describing! Big fat spark, noid light check 45 psi fuel pressure, 150 psi compression...I am stumped and I really need this truck right now...Any ideas, I haven't tried yet, would greatly help out...??? Hallelujah, and yeeehaaa brothers, I had an epiphany while cooking myself some dinner, and I just fixed it...the friggin coil !!!