Hi

I posted this in the 80-86 F-series forum as well, then I found this one....

I have an 85 F-250 with the 460 and an edelbrock carberator. My problem is that for some reason, when the truck sits for a couple of days, the gas seems to leak back down to the tank (can't see any leaks). The next time I try to start it, I have to crank it for about 30-60 seconds to get the gas back up to the carb.

My father-in-law has almost the exact same truck and his fuel pump turn on when the ignition is on, but mine doesn't turn on unless the engine is turning. I would like to either find out why the fuel drains back or set up the fuel pump to turn on when the key is on to charge the fuel system. Any help would be appreciated.

Thanks

 

Are you sure you have an electric pump? I thought it would be mechanical. At any rate, there seems to be a check valve that is not working properly somewhere in the fuel lines. I'm not familiar with that year truck enough to give any idea where to look. Does it do this even when you floor the accelerator a couple times before starting?

 

Yes, it is an electric pump, verified it in the front fuel tank. There also is what looks like another type of pump or the tank switching unit that is bolted onto the frame. My Chiltons doesn't give me any useful information about the fuel pumps or this other device.

I don't know where to look for the check valves and yes, it does this even when the accelerator is on the floor.

Thank you for your help.

 

This is what is called the "hot fuel" option. Basically, it was to prevent vapor lock. The piece on the frame rail is the selector valve, and that should have the check valves in it.
How long does the truck have to sit for before you have to crank it for a long time?

 

The newest Haynes manual 36058 is better than the old one!
I was screwed until I got the newer one!

If you have the 460 HOT FUEL system, your system is NOT on page 4-13 (NON HOT FUEL) like it looks at first!
It's actually on page 4-20 for the two "HOT FUEL" systems used!
Mine BTW is 15.3b

I just went through the whole fuel system on my 85 F250/460 and it has an oil pressure switch that allows power through the inertia switch while running as well as a wire from the starter relay supplying the pump with power while cranking the motor until it starts up.
If there were no power while cranking, until the oil pressure builds up, that might make it take longer.

I also put an extension in the fuel line and a glass in line filter and a fuel gauge on the drivers side fender so I can see the fuel and pressure while testing the systems involved!

I have a trashed fuse slot where the oil switch gets its power from and have it powered through the ignition system for now (it also bypasses the inertia switch) until I can fix it.

 

Ford_Six, generally, its a couple of days it has to sit before I really have to crank it. I talked with a mechanic here and he told me what Archangle said. It has an oil pressure switch in it and the pump won't start pumping until oil pressure is present. He didn't recommend bypassing it. He also told me that part of the problem could be because the edelbrock carberator that I have on it. He said they are known for draining like that and recommended I put an off-road needle/seat kit in it.

As for those check valves. I wil lsee what I can find out about that.

Thanks for the great information

 

excellent answer , respectfully,bob

 

I think part of the problem is because of he oil pressure switch. I don't have anything running from the starter relay to the pump. I dont know if this would work or not, but if I put a wire from the relay (on the starter side of course) to the fuel pump relay to turn it on while the starter is cranking then the oil pressure switch will keep it on. The only thing that concerns me is if I put it on the same wire as the oil pressure switch, when the switch turns on, will it try to power the starter too?

I did talk to another friend and he thinks part of the problem with the fuel draining would be because I have an edelbrock carb on it and he says they can do that. He suggested I put on off-road needle and seat kits. Does anyone out there think that would help?

Thanks

 

I have no power to my oil pressure switch, so I went from the ignition box on the drivers fender to the relay power wire so I have fuel pump pressure while the ignition is on as it bypasses the inertia switch that is between the oil switch and the fuel pumps.
When I get a new fuse box, I will trace the circuit to see that all is OK and hook up the oil and inertia switches.

This would also help you as when you turn the key on your pump will prime your fuel system even before you crank it!

 

I have an 86' F350, 460, auto, dual tanks with electric fuel pumps. I posted a problem regarding blowing the fuse for the fuel pump, and the fuel pump running with the key off on 2/21 (lengthy story). Yesterday I went to attempt to locate the problem, and now I have no power to the pump at all (fuse is good). I have the factory service manuals that outline the different relays and circuits. Where do I start? How do I identify if the "hot fuel" option? Can I just convert the system to a mechanical pump getting rid of the carb circuit and fuel pump control. I love things that are mechanical. Anything will help.

littlebuddy

 

"I have an 86' F350, 460, auto, dual tanks with electric fuel pumps. I posted a problem regarding blowing the fuse for the fuel pump, and the fuel pump running with the key off on 2/21 (lengthy story). Yesterday I went to attempt to locate the problem, and now I have no power to the pump at all (fuse is good). I have the factory service manuals that outline the different relays and circuits. Where do I start? "

Is the inertia switch button pushed in and has power?
If not, is the fusible link at the starter relay good supplying power to the inertia switch?

I would then go to the pump wire at the selector valve and check for volts after the valve, then follow the wires in the diagram back testing at the connections until I find 12 V, then the problem is between the two.

You could start at the beginning, chase the voltage from the pump to the battery, checking (or for wire continuity without the battery connected) at every connection for every circuit.
Or just chase the power on volts until it stops when it should not.


Continuity to the fuse from the disconnected pos battery terminal!
Continuity to the oil switch from the fuse!
Continuity to the fuel pump relay from the oil pressure switch!
And when there is no continuity to that item, there is a break in the wire between the two.

If all the wires check out OK, then start testing the relays and switches.

"How do I identify if the "hot fuel" option?"

Do you have a fuel return line connection "t" in front of the carb? Or 6 fuel connections at the selector valve and 5 wires on the connector?
If so, you have it!

Page 4-20 (picture 15.3B and 15.3C) are the hot fuel. (HARD TO TEST)
Page 4-13 (picture 11.17) is the EFI system. (not too simple/not too bad)
Page 4-12 (picture 11.3B) is carb/non hot fuel (easy and simple).

Then check the dash switch to see what the wire connector looks like and match it to the shape/picture in the book.

"Can I just convert the system to a mechanical pump getting rid of the carb circuit and fuel pump control."

The in tank pumps will kill the newly added pump as it will act as a restrictor and you cant select the tanks if the problem effects that as well.

I had to bypass the fuse and oil pressure switch jumping the cutoff relay to a key on power source that was right by it to get mine going.

 

Thank you very much. I will start with this and let you know. littlebuddy