No power to fuel pump on 20R. Can I bypass the auto-shut off?
06-03-2017, 07:10 PM
#1
No power to fuel pump on 20R. Can I bypass the auto-shut off?
Truck is a 1975 20R. Daily driver so I really need to sort this out.
I was driving yesterday and the truck died suddenly, no warning. Started once or twice and then nothing. I've traced it to an electrical issue not giving power to the fuel pump and think I have a solution but could use some advice.
Here's the situation
Fuel pump works when given 12V directly
The wire to the tank gauge gets 11v when I turn the key to on and then in 1-2 seconds drops and sort of cycles. I've got a cheap multimeter so I can't tell exactly what it's doing
The wire to the pump gets no voltage, ever. Key to on does nothing, cranking does nothing. No obvious breaks in the wiring but I'm not sure where it goes to once it comes in thru the firewall.
The oil shutoff wire (black and red wire that goes to the low pressure gauge) has been hanging loose since I got the truck. Grounding it doesn't change anything.
Fuses are ok.
I guess there's some kind of relay in the fuel pump circuit that can cause it to shut off the pump? Procedure to check the pump is to take the wire off the oil sender which is an auto-shut off in case you lose oil pressure and it can't be that because it's been hanging loose for years.
I could pull a new wire off of the coil circuit and run power directly to the fuel pump whenever the key is on, but is there any reason why that would be a bad idea? Could this be a simple fix somewhere in the fuel pump circuit? I don't know where to look.
I was driving yesterday and the truck died suddenly, no warning. Started once or twice and then nothing. I've traced it to an electrical issue not giving power to the fuel pump and think I have a solution but could use some advice.
Here's the situation
Fuel pump works when given 12V directly
The wire to the tank gauge gets 11v when I turn the key to on and then in 1-2 seconds drops and sort of cycles. I've got a cheap multimeter so I can't tell exactly what it's doing
The wire to the pump gets no voltage, ever. Key to on does nothing, cranking does nothing. No obvious breaks in the wiring but I'm not sure where it goes to once it comes in thru the firewall.
The oil shutoff wire (black and red wire that goes to the low pressure gauge) has been hanging loose since I got the truck. Grounding it doesn't change anything.
Fuses are ok.
I guess there's some kind of relay in the fuel pump circuit that can cause it to shut off the pump? Procedure to check the pump is to take the wire off the oil sender which is an auto-shut off in case you lose oil pressure and it can't be that because it's been hanging loose for years.
I could pull a new wire off of the coil circuit and run power directly to the fuel pump whenever the key is on, but is there any reason why that would be a bad idea? Could this be a simple fix somewhere in the fuel pump circuit? I don't know where to look.
06-03-2017, 07:41 PM
#2
Nevermind, found this thread: http://toyotamotorhome.org/forums/in...iring-diagram/
