88iroc-Z

iTrader: (1)

this is actually for my brothers car which we have not been able to get running correctly.
the car is a 94 Z28 with the LT1.

the car was bone stock up until about two months ago, and my brother is the first owner, then we encountered a problem withthe optispark. and, decided to replace with a GM high performance optispark from summit.
while the car was under construction we also added
a LT4 HOTCAM kit(.525lift,1:6 roller rockers, LT4 springs for hotcam)
GM double roller timing chain
GMHP waterpump
Longtube ceramic coated headers
3" Y-pipe
Magnaflow converter
flowmaster exhaust
K&N filter
and removed MAF screens

then, the car would not start.
then we replaced the Spark control module, and redid ALL grounds.
now vehicle starts but died after warm-up.
after cooling down car started after a few cranks and kept running.
BUT, After we shut off the car when it is warmed up it will crank over but not turn on.

So, we though we had a leaky injector fludding the engine, since after a few attemps of starting the car with the pedal at WOT it would start.

then, this weekend we replaced injectors with 30# accel injector, and also ordered a aeromotive FPRwhich we haven't installed yet.

And, we are still having the same problem.
car runs fine(we still haven't gotten on it yet since we are still having problems)but won't start after it gets warm.

So what could be causing this, we are going to be working on the car tommorrow but we have run ou tof ideas.
So do any of you know what could be causing this or have any idea?

fire350tpi

if it were a third gen id say ICM ( ignition control module) but lt1's have optispark and such i dunno much about the system tbh

But gl with it

88iroc-Z

iTrader: (1)

I was reading some similar problems that other people were having and they said it could possibly be the ICM ( ignition control module), did not have enough dielectric grease and would heat up, although when we replaced the ICM with a new one we installed it with the dielectric grease it came with as well as a little extra that we had also bought a tube of, so I doubt it was that?
thanks though...

also I don't know if it would be a problem but the 3" Y-pipe comes about 3/8"-1/2" from he fuel lines although we wrapped the fuel lines with a header wrap to help protect them, so could this still induce vapor lock with them protected this way?

If not what other ideas, or what should we check?

GTA_JOE

Is the starter turning the motor over and it won't fire, or are you turning the key and nothing is happening at all?

fire350tpi

If the icm is working correclty, id have to say something is making it not start only when warm, brings to mind overheating of a component nessasary to start, Fuel pump ( fuel pressure) .. I think we know spark is good?

So warm it up then test the fuel pressure while its happening ( or the classic hook the fuel pressure up and tape it to the window and see if it drops when ur driving)

88iroc-Z

iTrader: (1)

yes, the car does crank over.


I was going to take my fuel pressure guage by tommorrow to test it, but the car doesn't die on us it just won't start if we shut it off once it had been warmed up.
also the fuel pump never gave us any problems before?
could that still be the fuel pump?

fire350tpi

u never know, just test all systems when it wont start, Fuel line's could be geting vapor lock or fuel pump could be overheating who knows
also check for spark when it wont start..

and do's your car have vats? that cuts of the fuel injectors perhaps your key chip could be worn out or somewhat

edit: Just had an idea.. Maybe ur fuel pump relay isnt working correctly when its warm if u dont hear the pump prime the relay may be half gone and slowly failing ( hope this helps!)


Anyhow GL

88iroc-Z

iTrader: (1)

thanks guys I am about to go by and work on the car and try your suggestions.
thanks for your help and I will post result and/or maybe more questions if it still won't run right.

thanks again
-Daniel

88iroc-Z

iTrader: (1)

just got home went through everything we could think of and nothing worked.

any more suggestion?

fire350tpi

Did u do it when it was /warm and not starting?

88iroc-Z

iTrader: (1)

sorry I didn't reply sooner, I have had a terrible cold and haven't done much of anything.

The car is doing the same thing as before, and fuel press. seems fine at ~40psi.
Also the car would die whenever we tried to hit the gas pedal once it was warm(200+)
I really don't know of anything else to check????

any more I deas guys?

thanks for all of the help,
-Daniel

rgarcia63

On the subject of injectors did you update the injector size in the ECM? If not put the old ones back (if there's nothing wrong with them) until the problem is solved then install the 30#s and update the system, and adjust the FPR.

Vapor lock isn't out of the question, but it's at the bottom of my list of possiblities.

If you suspect the fuel pump:
Fuel pumps supply fuel volume; they do not create pressure in the fuel lines (they require enough pressure to open the check valve which isn't much.)
In a return-line system the fuel pressure regulator restricts the return fuel flow in order to create pressure in the supply line.

The pump will only affect the volume when it's voltage, and current draw is abnormal.

Supervisor42

It sounds like it could be a wiring problem in the circuit that powers/fires the ignition coils. If the fuel pressure is there when it is hot and won't start then either the ignition or injector drive may be going lame. Like a bad connection that is heating up.
I don't know much about optispark either. When it cools down and does start, if it doesn't act like it was flooded, you could carefully spray it with starting fluid next time it won't start to verify a no-fuel condition. That would let you take the 50/50 and know if it is fuel or ignition. If it fires, then it's a fuel problem. If it doesn't then it's ignition.

88iroc-Z

iTrader: (1)

ok, I will try this saturday, because I am not going to be able to work on the car until then because of work.

Hopefully this helps me some more.

I am also going to check the adjustment of the roller rockersto make sure they are not to tight and once the car warms up and lifters pressurize it could affect the car wanting to start.
Also, it did it once before with the factory injectors and FPR, but it would idle OK (around400-500 rpm in gear) but when we went to give it some gas in "park" while it was around 210* it would just die.

hopefully that give you a bit more insight and thank you once again for your suggestions and helping me trouble shoot this problem.

hitman0187

I think supervisor42 is closest to the resolution. I have the same issue in a 3rd gen currently and have replaced everything except running a painless wiring kit and the issue still pains me. the bad news is it only gets worse, for years i dealt with the no start when hot. it progressed to stalling when warm and not starting. im probably going to do the re-wire regardless. the quality control in gm sensors and wiring in the 80's was really bad. never saw a corvette with these issues...

hitman0187

i also wanted to add in my case its a no spark condition when it strikes, i would gather from the talk above its the same deal. pull one of the plugs when its no start and verify