I’ve been working on a 96 z28 LT1 for a couple weeks now. The opti was replaced and is firing, the car cranks, has good spark, fresh fuel, injectors are operating but it’s flooding itself out and won’t stay running. I can get it to start once a day and run at half throttle for about a minute at 800 rpms once it runs that one time it dies and won’t restart just sputters. Anyone else battle an issue like that?

 

Several possibilites:

Have you checked the fuel pressure? Stock system operates at 43.5 PSI, minus compensation for intake manifold vacuum. If you turn the key to run, the fuel pump should prime for 2-seconds and shut off. Pressure should reach at least 40 PSI, and drop very slowly when the pump shuts off. A rapid drop in pressure can indicate a leak in the fuel pressure regulator or in one or more injectors. A failed diaphragm in the fuel pressure regulator can dump fuel into the intake manifold thru the vacuum compensation line. Excessive fuel pressure causes excess fuel flow.

At idle, fuel pressure should be 43.5 PSI (GM accepts a range of 42-47 PSI) with the vacuum compensation line OFF the fuel pressure regulator. When you REATTACH the vacuum line, pressure should drop about 8 PSI below the "no vacuum line" pressure, in the 35 PSI range (stock cam, less drop with a more aggressive cam).

Another cause of excessively rich cold start mixture can be a faulty coolant temperature regulator. The colder the coolant, the richer the PCM sets the cold start A/F ratio. If the PCM doesn't see the coolant warming up due to a faulty coolant temp sensor or harness wiring, the engine is going to run pig rich and stall. There's a code for a faulty coolant temp sensor, but it only sets with virtually total failure of the sensor or wiring - open circuit or shorted circuit. A mis-calibrated sensor won't be detected.