1990 fires up then dies

[Stan Masta]

Fuel pump shuts off after 2 seconds. FP1 relay checks out. ECM Code 56 even after reset (coincidence?). Vacuum sensor checks out with 0.555 V at atmospheric. Any danger in forcing FP1 with jumper? Couple of times engine ran for a while with AG jumper in ALDL. Complete fuel pump setup replaced 2 years ago and worked great until recently. All ideas welcome.

[QB93Z]

Have you been able to verify that both fuel pumps are running when the Ign Key is in ON and Engine is OFF?

If you can jumper the FP relays, I would try that one at a time, and put a gauge on the fuel rail.

Another variable is that there are check valves in the fuel pump assembly that can fail causing fuel flow to short cycle in the tank.

Good luck,

Jim

[Stan Masta]

Hello:
I do appreciate your quick response. Having read through a portion of the shop manual re Code 56 I am beginning to suspect one of the pumps. As a matter of fact I do not remember why I replaced the OEM fuel pump ***'y in first place. I will try to put it back in and see if that cures it. What bugs me though is that after the intitial 2 second fuel pump run there is absolute silence as if the ECM kept the pump(s) from running.
Thanks again for your input.
Stan

[Kevin]

Sounds like your primary pump is bad

[Stan Masta]

Kevin, thanks for your encouragement. I already dug up the old OEM pump set and will put it back in tomorrow. Much obliged.
Stan