Marc1122

I have a 1995 z28.
Car was running fine until yesterday.
If you drive it fairly easy it runs fine.
If you get into it fairly hard when it shifts to second gear it dies.
It will refire after a far amount of cranking.
Don't know quite where to start with this issue, any help would be appreciated.

Injuneer

Is the engine stock, or modified? If modified, what has been done? How many miles on the engine"

Have you scanned it for codes, and checked the fuel pressure? When you are trying to restart, during the "far amount of cranking", do you have spark to the plugs?

Does the car still have a cat? Could it be plugged up?

Marc1122

6k miles on crate engine.
Stock no mods.
Cat deleted.
Have not checked fuel pressure or spark while trying to restart yet.
.

Chimera96

get a fuel pressure gauge. It should be 43.5 with the vacuum line removed from FPR (or around 37 psi with it on). If it is good at idle...rev the motor to see if it drops....it should not. Ideally the gauge has a hose long enough on it to tape gauge to wond shield. If at "sustained" WOT it drops...fuel pump is failing

You mention it will run OK at light throttle but die when you get on the gas...this could be due to low fuel pressure from a fuel pump failing...or a very clogged fuel filter

rule out a fuel pressure first and if that checks out move on to ignition

Marc1122

Got a chance to check fuel pressure. It all checks out.
Sitting in park, once you bring the car to about 4K it shuts down.
Now I am really puzzled.
Once again any help is appreciated

Injuneer

You have to test the fuel pressure with the engine under load, out on the road, at 4,000 RPM. Tell us the numerical result... not "all checks out".

I'll ask again..... have you scanned it for codes?

Marc1122

I scanned for codes. No codes. Fuel pressure under load on the road was36 psi. At 4000 rpm it shut down going down the road. I went ahead and installed a new fuel pump and filter. Did not change a thing still shuts down at 4000 rpm sitting still or going down the road. I am assuming now it is ignition?

94Z28LS1toLT1

what happened to fuel pressure at 4000 rpm? Chimera and Fred said to check fuel pressure at WOT to see what the pressure will do at that rpm. And y buy a fuel pump n filter if u actually didn't need it.

​​​​​​​because now you're having the same issue without any change.

Marc1122

36 psi at idle. 36 psi at 4000rpm then it dies.

Marc1122

Ok. Here's an update. Now it will die at idle in park sometimes or not till it hits about 4000rpm. It's sporadic. When I try to immediately refire there is no spark. But after 10 or 15 minutes it will fire right back up

Injuneer

Have the ICM tested, making sure the shop gets it good and hot.

Fuel pressure at WOT, high RPM should be at least 40 PSI. Part throttle rail pressure will drop proportional to intake manifold vacuum, as described in an earlier post.... e.g. 36 PSI.

Marc1122

ICM bad. New ICM runs fine now.
Thanks for all the help

Marc1122

Let me retract my last statement. Icm did not fix it. Ran great in the shop. Took it out for a drive. Didn't make it a half mile and it died. Now the problem is more sporadic. Starts and dies. Then it might start and make it a few hundred feet then die. Or it might start and go a couple miles then die. It's all over the place. Like the problem is getting worse.

Injuneer

Check to see if the ICM is getting the signal from the PCM to fire the coil.

Courtesy of Shoebox

4th Gen LT1 F-body Tech Articles

What scanner are you using to try and pull codes?

TobyZ28

This sounds like an opti on it's way out if you've ruled out the easy to check ignition stuff (ICM, Grounding etc). Because the ICM made some difference but didn't solve the problem I'm leaning towards ignition/electrical related for sure.

I would rule out wire arcing, failing spark plugs etc as those issues would be a more consistent problem (it would run rough all the time or at certain rpm and loads), if the ICM / Coil is good that leaves you with Opti.