1988 regal 2.8 runs for 5 minutes stops

we have replaced crank position sensor, ecm/ coil packs and computer. got good pressure on fuel rail.

starts cold, will run normally for approximately 5 minutes before it dies and will not start.

sometimes we can hold accelerator to floor and it will "hit" a few licks but promptly dies when accelerator is released.

we've checked fuses and relays; what are we missing?

When it won't start, that's when it is easiest to check....

Check fuel pressure....should be around 40psi.....

Check your vac line to the fuel pressure regulator...if you smell gas or see gas in the vac line, bad regulator...

Try this.....disconnect the injector harness, this comes out from under the top of the engine on the passenger side.....crank the engine several times....it shouldn't start.....now have someone spray carb cleaner into the intake....if it starts and runs as long as you spray, it's a fuel delivery problem......recheck your fuel pressure when it won't start.....if fuel pressure is ok, then you could have an injector problem.....

This is a multiport engine, which means three injectors fire at the same time, 2-4-6, and 1-3-5......if an injector goes bad(shorts), the injector driver in the ECM(quad driver), shuts down not just that one injector, it shuts down all three,,,,