Hey everyone. About 8 months ago I bought a 93 z28 M6 off my neighbor. The neighbor had let it set for a while because the optispark had gone out on it. He bought a replacement one (no-name brand) but couldn't replace it himself. I replaced it and have had no problems except for a starting problem that replacing the injectors fixed (just a little more expensive than a good cleaning).
Recently it has started stalling on me. It usually happens after about 15-20 min driving and has happened at stops, WOT, and normal driving. The check engine and gauge lights come on and if the car is still moving will not let me pop the clutch (starts sort of, but no power and won't stay running). Most of the time it will restart in just a second or two, sometimes you have to let it sit for a couple of minutes. After you get it restarted it will sometimes stall again in a short bit, or it will run for a while 15-20 before it will happen again.
I took it to a speed shop and of course it never failed with them and while they had it hooked to their scanner/pc it showed everything working perfect. It never pops codes either. I have replaced the fuel filter (incase it was water in tank), new injectors, tested the ignition control module till very hot, and coil. According to the manual the optispark is the likely culprit, but was hoping anyone out there could shine some light on say a nice $3 part that would cause this!

 

sounds like your on the right track. the first things that come to mind are the opti, the coil and the ignition modual. what about spark plugs and wires. when were they changed last.

 

Plugs and wires were checked when I took the opti off last time about 8 months ago, and had been replaced (both) about 15k before that.

 

Could also be a fuel supply problem, like an overheating fuel pump. Will it ever quit at a convenient time where you could check for fuel pressure at the rail?

 

I have tried to run it for long periods in my driveway hoping it would quit. Unfortunately it likes to die on the street, usually at lights or someplace with no turn off. I was told by the previous owner that the fuel pump was replaced 40k ago when they rebuilt the motor (someone poured sugar or sand in tank). But I can't verify that. So when it dies just check the pressure at rail (I think I saw that mentioned in the manual)? If no pressure then possibly fuel pump? A couple of times when it died it took me quite a few minutes to restart it (had a weird smell from engine compartment). Acted like it was turning over and sparking fine and even coughed a touch like it wanted to fire, but no fuel was available. Sorry sort of a very novice mechanic, good at directions, not good at truly understanding the motor.

 

If it's a fuel problem that's killing the engine, then the fuel rail should be for the most part empty of gas. If you don't have a gauge, you could do a quick check by pushing in on the valve with a screwdriver to see if gas squirts out, and if with any force. Cover it with a rag first though, just in case.

 

Thanks, I'll give that a try and see what happens.

 

Got a fuel pressure gauge and and hooked it up. Turned on key and showed 41psi, low end of normal according to book. Started car and psi jumped to 45-47. Let it idle, no change. The book says it should drop 3-10psi.

 

From the pressure readings you obtained, it would seem that either the pressure regulator is bad or there is a lack of vacuum to the pressure regulator. Check the vacuum hose to the regulator for leaks, cracks, etc..
With engine idling the vacuum to the regulator is high, and the regulator pulls the pressure down. With engine at WOT the vacuum to the regulator is low and the regulator allows the pressure to rise to the pump's max. You can simulate WOT by pulling the vacuum hose from the regulator.
High pressure at low speed could result in an over rich condition and could cause the engine to die.