1990 fires up then dies - ZR-1 Net Registry Forums

Stan Masta · 03-20-2015

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 · 03-20-2015

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 · 03-20-2015

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 · 03-20-2015

Sounds like your primary pump is bad

Stan Masta · 03-20-2015

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

03-20-2015	#1
Stan Masta Join Date: Dec 2005 Posts: 5	1990 fires up then dies 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.

03-20-2015	#2
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,689	Re: 1990 fires up then dies 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 __________________ If it isn't fun, you aren't doing it right! 1990 Black ZR-1 - sold 1993 Quasar Blue ZR-1 1994 Competition Yellow ZR-1 1995 Dark Purple ZR-1 Maryland State Coordinator WAZOO Member

03-20-2015	#3
Stan Masta Join Date: Dec 2005 Posts: 5	Re: 1990 fires up then dies 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

03-20-2015	#4
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,632	Re: 1990 fires up then dies Sounds like your primary pump is bad __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

03-20-2015	#5
Stan Masta Join Date: Dec 2005 Posts: 5	Re: 1990 fires up then dies Kevin, thanks for your encouragement. I already dug up the old OEM pump set and will put it back in tomorrow. Much obliged. Stan