Manually switched Electronic furl pump ?

[cougar190]

My truck, 1994 Ranger SXT 4.0 ltr 5 spd. Was saved from a field where it had sat for years. Had to do some work to make it road worthy. Fast forward to present. Was driving until recently when it started blowing fuel pump fuses. Eventually traced problem to previous owner straight wiring from output side of power distribution box to fuel pump bypassing safety cut-off switch (I'm cool with that). I had replaced the fuel pump before I found this out. Now my fuel pump works intermittently. I had gone through the wiring system prior to this so I know everything is functioning. It seems like the problem is located at the fuel pump relay. I've tried numerous relays I have around (kind of a parts junky), swapping relays doesn't help. Cleaning connectors where relay plugs in hasn't either. When I cross between pins 30 & 87 it fires and runs fine. So I'm wondering if I can run a switch between these 2 points and just operate my fuel pump manually. Thanks for your thoughts; Cougar

P.S. If your have any thoughts on what my problem is I'ld appreciate those as well !

 

[adsm08]

Sounds like the problem is in the relay control circuit, which involves the computer. Both hot pins of the relay are hot key on, the computer grounds the coil side to close the relay. A wonky wire there, or a failing computer can cause your issue.

As for putting it on a switch, it can be done safely. That is a return style system, so the pump runs full bore all the time anyway.

 

[RonD]

Pins 30 and 87 are the LOAD of the relay, fuel pump power

Pins 85 and 86 on the relay are the controls, on/off

Test which one has 12volts key on, that 12v is from the EEC(PCM) Relay, if no 12v then that's the problem, why relay is not working

The other one is for the Ground from computer(PCM)

This ground wire is also found on the OBD1 test port next to the fuse box
Look at second drawing here: https://www.therangerstation.com/tech_library/OBD_I.shtml

Fuel Pump Ground slot is labelled
If 85 or 86 has 12v key on, then Grounding this slot on the OBD1 port will activate fuel pump relay with Key on, so much simpler fix
Key on fuel pump on, key off fuel pump off

This would mean pin 22 on computer or its wire is bad, computer should Ground pin 22 wire to activate fuel pump
But only for 2 seconds key on, then full time when engine RPMs are above 400(engine started)

 

[cougar190]

Hey Thanks guys! Things rough right now. Stroke at end of Feb., but trying to get around to stuff ! ...cougar...