95 lumina no hot restart

My lumina will not restart after it's been running for a while. I've changed the fuel pump and filter, the spark plugs, the crank pos. sensor and the engine coolant temp. sensor. Not sure where the little black valve is to check the fuel pressure after it won't start but i know the fuel pump is engaging(can hear it). I've checked the spark while trying to restart and it looks good i guess(distinct white spark to the tip). Haven't got a code check yet because the check engine light doesn't always come on or stay on. Need some advice on where to turn to next. (ICM, injectors,battery ect.)
Thanks very much!

Welcome to AF. 3.1 ?Get a fuel pressure gage on the injector rail, also try spraying carb cleaner into the intake, see if it starts, post back results.

Haven't got a guage yet but it will restart with starting fluid. thanks for your reply.

Then you have a fuel delivery problem start with the FP test.