4.3L cobra electric fuel pump cutting out

[jon705]

As part of an engine replacement for my 1990 OMC cobra it was necessary to swap in an electric fuel pump as the replacement block did not have a cutout for the mechanical pump. When wiring I included a relay and oil pressure safety switch.

The problem I'm encountering is that the engine will run for about 30 seconds then starts to stumble and will finally cut out due to lack of fuel. If I pump the throttle then turn the key she'll start right back up, run for several seconds then again stumble and finally cut out due to lack of fuel. When she runs I listen closely to the fuel pump and can hear that it cuts out.

Any thoughts as to what is causing the pump to shut off? What tests can I perform to track this down?

 

[JON NEELEY]

Re: 4.3L cobra electric fuel pump cutting out

Jon, sounds like to me your relay allows you to get engine started with pump then relay shuts cutting fuel but you need to pressure test fuel line via the sticky at top of page "how to test fuel system"

 

[Maclin]

Re: 4.3L cobra electric fuel pump cutting out

Regarding the oil pressure safety switch, make sure you have it wired correctly. Some have two wire connections, some have 3 and the wiring is different, follow the diagrams you got with the switch. Also be sure it is mounted in a good spot to get constant and accurate oil pressure.

 

[jon705]

Re: 4.3L cobra electric fuel pump cutting out

Wired the fuel pump directly to a 12v source last night and she ran without issue.

Next hooked a 12v source directly to relay 12v and she ran without issue.

The oil pressure switch is definitely the culprit because when I finally wired that back in she would fire up, run 30 or so seconds then starve for fuel and cut out. I wired the switch according to the instructions where NC is going to the plus side of the coil, NO is going to the yellow/red wire on the assist solenoid and C goes to 12v on the fuel pump relay. I'm certain the C terminal is wired correctly. Should I use different sources for the NC or NO poles?

 

[bruceb58]

Re: 4.3L cobra electric fuel pump cutting out

Depending on the nomenclature I would swap the NC and NO connections. The C connection needs to go to the coil of the relay.

I am assuming that with no oil pressure the switch is connected between the C and NC right?

Kinda like this except you have a relay in there instead of going straight to the pump.

 

[Maclin]

Re: 4.3L cobra electric fuel pump cutting out

Can you get a rough drawing posted of the wiring routing with the switch and relay routing? I think it is the terminal choices, but I have too many ideas and need to narrow it down based on how you have the routing now.

 

[Maclin]

Re: 4.3L cobra electric fuel pump cutting out

Thanks Bruce, I was typing in mine while you were posting.

 

[jon705]

Re: 4.3L cobra electric fuel pump cutting out

Depending on the nomenclature I would swap the NC and NO connections. The C connection needs to go to the coil of the relay.

D'oh :facepalm: then Woohoo!! Swapped the NC and NO and she runs great! We'll be on the water this weekend.

Thanks for taking the time to reply.

 

[Maclin]

Re: 4.3L cobra electric fuel pump cutting out

Good deal