94 z28 lt1 shuts off
 

good day all new to the forum
well my z28 shuts off while driving, I've changed out the mass air flow sensor, icm, manifold sensor, just shuts off like i turned the key off, i was getting a engine light but not anymore, sometimes it starts right back up other times i have to wait 5-10 min, i know other lt1 have had this problem, is there a way to rule the opti spark out, any help please
cheers

Re: 94 z28 lt1 shuts off
 

Scan it for codes. If the SES light was on, the codes will be stored in the PCM, unless you pulled the battery cable. And, one code that shuts the engine down or prevents it from starting is DTC 16 for the cam position sensor in the Optispark. That code does not turn on the SES light.

Have you checked for spark at the plugs when it won't start?

In the meantime, here is a way to check that the Opti signals are reaching the PCM/ICM/coil:

Courtesy of Shoebox

4th Gen LT1 F-body Tech Articles

Re: 94 z28 lt1 shuts off
 

thanks for the quick reply will start looking into with your ammo
cheers

Re: 94 z28 lt1 shuts off
 

A dead giveaway of the Opti failure is missing tach indication while cranking. Normally it should show 100-200 rpm while cranking.

Re: 94 z28 lt1 shuts off
 

so i was playing around and when the engine warms up it shuts off, i pull a plug wire and put a spark plug on the end to see if i got power and crank the engine and there is no spark so does that mean my optispark is going.or my coil

Re: 94 z28 lt1 shuts off
 

Did you watch the tach while cranking? No movement usually means a dead Opti.

Re: 94 z28 lt1 shuts off
 

so it was not starting after it warmed up and then shut off on me, so i put a spark plug on the end of the wire to see if there was spark while cranking it over, no spark, went to check the tach to see if it moves and it starts up normal, so now i have spark, i'll bet when it dies on me ill have no spark at the plugs again, let it cool down starts up fine,

Re: 94 z28 lt1 shuts off
 

When it loses fire, do the tests in the link that Injuneer gave you. That will help narrow it down.

Re: 94 z28 lt1 shuts off
 

ok did injuneer's test and my numbers came back good, only thing is when i was testing while cranking over the engine i was suppose to see a 1-4 volts while cranking, my volts were all over the place, i stuck my multi meter on the icm harness b to ground. How can i test my coil while cranking the engine over

Re: 94 z28 lt1 shuts off
 

That's normal at cranking speed.

Re: 94 z28 lt1 shuts off
 

so its got a new icm did the mod to move it away from the block, it has an msd coil that looks older could it be heat soaked

Re: 94 z28 lt1 shuts off
 

so went and put a new coil in it, ran for 10 min then shut off, would not fire up again
so it now has a new coil,icm,tbs,mass air flow sensor, map sensor, wires are newer,
So when the car warms up and shuts off i have no spark,and doesn't want to start right away, i know my coil and icm are good, so could it be the pcm or opitispark

Re: 94 z28 lt1 shuts off
 

Were you using the ac scale, like the instructions said?

Re: 94 z28 lt1 shuts off
 

Just to be clear, those are not my instructions. What I gave you was the link to SHOEBOX'S test procedure. You need to listen to him. :D. ......and Gary!

Re: 94 z28 lt1 shuts off
 

its all good

cheers