LT1 has spark, fuel, comp, timing but no start

[97-Z28-HI]

Some history. My 97 Z28 (all stock) was running OK, but with a bit of a miss. If I drove it everyday it would fire right up, however if I let it stand for more than 24hours it would behave like it was flooded and not start. The only way I could get it started was by removing the fuel injector fuse, then replacing it. This would take several attempts but eventually worked out and after blowing some smoke out the tail pipe, things would clear up and the car would go back to running and starting right up. Finally, one morning after dropping my daughter at school I went to start the car, it cranked, then stumbled and didn't fire up. On subsequent attempts it continued to act like it was flooded, but I was not able to get it started.

Changed out the spark plugs and wires, tried 2 different optisparks, replaced crank sensor and tried a new pcm. Checked connections and grounds. Compression test was OK (between 120 and 140). Timing is OK. Has fuel. Has Spark. Cranks but does not fire up and run. When we attempt to crank the car we had the battery jumped to another vehicle to make sure that it had enough juice. The mechanics that have checked it out say they are stumped. What are we missing??

Here is a list of some specific items that have been checked;


Fuel pressure is correct per spec at 45+ PSI.
fuel bleed down was checked and the pressure held beyond what the spec is..

injectors have been pulled and checked for leaks and are OK.

Spark has been checked with a spark checker, and pulled plugs and have watched them spark while cranking. The fuel injector pulse appears to be in time with the spark.
.
Originally, when the car was still running, the codes on the computer were PO300 (random missfire) and PO441 (Evap emission control incorrect purge flow).

[Hi I Drive A Z28]

Hey bud, have you checked your ignition coil and your ICM ? I had the same issue awhile back with my 93 Z. I replaced everything i could think of, fuel pump, filter etc. I replaced the opti, the coil and the icm twice and finally got it to fire. Also I had a bad ground where the ICM bolts on to the front of the head. Now I can let her sit for about a week and a half and not mess with her and she'll fire right up every. I know some auto parts stores can check ICMs. Hope this helps

[cocobolo95]

I think 120-140 psi is kinda low for a lt1 engine. I would expect in the 180 range on one of these engines, unless you have a very long duration, high lift cam in there.

As an example, I used to get 140-150 psi from an 8 to 1 compression Fiat engine. Lt1 comes with 10.5 to 1 compression.

Not wanting to start when fuel and spark is good is one of the classic symptoms of a blown head gasket. Remember the symptoms of hg failure depend on where it's blown out at. Most people think that hg failure automatically means water in the oil, but it doesn't. There are many symptoms, as stated, depending on where the gasket blew.

Having worked on Fiats for many years, they were the king of head gasket failure, I've seen it all.

[97-Z28-HI]

Thanks for the advice guys. Can the ICM still be bad if you are getting spark? How about the ignition coil? I've been thinking about the ICM and Coil for a while but thought that since we had spark they must be ok???

In regards to the compression numbers, I was mistaken. They were all above 150.