1984 250 460 dual tank- trouble priming fuel lines

[84-460-Project]

So after 2 days of trying I'm finally admitting - I'm lost.

1984 F250 460 "hot fuel option" dual tank

Replaced w/new parts:

- Rear fuel tank

- Rear sending unit

- all steel fuel lines

- Fuel tanks selector valve

- Fuel tank selector relay

- Fuel pump cutoff relay

- Starter relay

- Hot fuel option "t" value w/blue dot

I took the edelbrock 1406 carb off, cleaned it and made sure the floats are set and cleaned out jets, air ways and set the electronic choke.

I filled up both tanks half full and tried to prime the tanks in the following manner:

- Turning the motor over at least 25 times w/the fuel tank switch in the front and back position.

- Taking fuseable link T off the starter relay and connecting it, by a jumper cable, to the positive side of the battery to start the fuel pumps. I let the fuel pumps run for at least 25 min (I heard them running). This is both the front and rear.

I have (2) fuel filters. (1) on the engine side of the fuel tank selector valve and (1) on the engine side of the "hot fuel option - blue dot T valve).

I checked fuse 18 to ensure it wasn't popped.

I've managed to get fuel to the carb once and the truck started. It was pulling from the front tank. I tried getting fuel from the rear tank and no fuel was moving. I went back to the front and nothing.

I don't think there is a blockage in the fuel line, but I haven't run a bypass from one of the tanks past the fuel selector value to see if thats the problem. When I took the fuel filter (on the engine side of the fuel selector valve) off fuel was moving. Which makes me think the value is not blocking any fuel.

I did run the steel fuel lines up and along the firewall. The stock Holly was fed from the drivers side. The aftermarket edeblrock is fed from the passenger side. I don't think the extra line would tax the fuel pumps to the point they couldn't deliver fuel.

What am I missing?

 

[Gary Lewis]

I'll bet you are frustrated.

First, before going any further and before I forget, when you get this sorted out you may need to put a fuel pressure regulator on. Edelbrock's don't like more then 6 psi and the electric pumps can give too much pressure and overpower the floats, especially at idle. But, that can wait as you need fuel first.

Anyway, to troubleshoot I would break the system down and test it section by section. Pull the line from either the front or back tank off the selector valve and see if you get fuel there. If so, but it back on and pull the line leaving the selector valve - do you get fuel there? If so, keep going.

But I doubt you'll get that far before finding the problem. And, I'm suspecting the selector valve is the problem since it is a common thing in the issue. Maybe it is bad? Maybe there's a wiring problem?

By the way, those pumps aren't supposed to have full voltage other than when starting. There is a resistor in the line when in Run. I don't think you hurt them as the engine wasn't running and the voltage would have been something like 12 volts instead of the 14 volts with the engine running and the fuse link straight to the battery. But, I wouldn't want to run them a long time with full voltage.

 

[grumpin]

I had an intermittent problem getting fuel on my truck. The connector for the oil pressure switch is bad.

It's on the back of the engine. IIRC the sender for the gauge is there also. I don't know if the wire color is the same on a 1984 as my manual is for my 1986.

After the engine starts this keeps the Fuel Pump relay on. You could try jumpering the connector.

[85lebaront2]

Having lived with one of these for quite a while (1986 F350) I am pretty conversant with the system. The Hot Fuel Option Package T valve with blue dot. Mine had a 6 port motor operated valve that controlled both the supply and return lines, the pumps in these are extremely low pressure, spec calls for 5-7 psi so the two filters may be too much restriction. Can you hear or feel the selector valve switching? I just figured out what you are calling the T valve, it is the vapor separator and has an orifice where the 1/4" line attaches.

Other question, can you hear the pumps run? they make a not super loud whine, like a fan motor only muffled because they are submerged in the tanks. Fuse #18 is the pumps through the tank selector relay, fuse #15 is the tank selector valve control.

Here are the diagrams, if they aren't easy enough to read I can email them to you.

[84-460-Project]

Having lived with one of these for quite a while (1986 F350) I am pretty conversant with the system. The Hot Fuel Option Package T valve with blue dot. Mine had a 6 port motor operated valve that controlled both the supply and return lines, the pumps in these are extremely low pressure, spec calls for 5-7 psi so the two filters may be too much restriction. Can you hear or feel the selector valve switching? I just figured out what you are calling the T valve, it is the vapor separator and has an orifice where the 1/4" line attaches.

Other question, can you hear the pumps run? they make a not super loud whine, like a fan motor only muffled because they are submerged in the tanks. Fuse #18 is the pumps through the tank selector relay, fuse #15 is the tank selector valve control.

Here are the diagrams, if they aren't easy enough to read I can email them to you.

Good call on the fuel filters. I'll take them out of the line and see if I can get the fuel moving.

I can hear both fuel pumps running. The new one is very loud and the older one is weaker.

Both fuses are still good.

Thanks.

[84-460-Project]

I had an intermittent problem getting fuel on my truck. The connector for the oil pressure switch is bad.

It's on the back of the engine. IIRC the sender for the gauge is there also. I don't know if the wire color is the same on a 1984 as my manual is for my 1986.

After the engine starts this keeps the Fuel Pump relay on. You could try jumpering the connector.

I replaced the oil pressure switch. I'm not sure what (or where the) the IIRC is. Is this in the loop for the fuel system?

How do I jumper the oil pressure switch?

[84-460-Project]

I'll bet you are frustrated.

First, before going any further and before I forget, when you get this sorted out you may need to put a fuel pressure regulator on. Edelbrock's don't like more then 6 psi and the electric pumps can give too much pressure and overpower the floats, especially at idle. But, that can wait as you need fuel first.

Anyway, to troubleshoot I would break the system down and test it section by section. Pull the line from either the front or back tank off the selector valve and see if you get fuel there. If so, but it back on and pull the line leaving the selector valve - do you get fuel there? If so, keep going.

But I doubt you'll get that far before finding the problem. And, I'm suspecting the selector valve is the problem since it is a common thing in the issue. Maybe it is bad? Maybe there's a wiring problem?

By the way, those pumps aren't supposed to have full voltage other than when starting. There is a resistor in the line when in Run. I don't think you hurt them as the engine wasn't running and the voltage would have been something like 12 volts instead of the 14 volts with the engine running and the fuse link straight to the battery. But, I wouldn't want to run them a long time with full voltage.

Thanks. I'll follow your advise and section the system off to find where the bad connection is.

Where did you put the fuel pressure regulator?

Its a brand new fuel tank selector. I triple checked the wiring, but i'll go through it again.

How many starts should I expect to prime an empty fuel line?

Where does the electric signal come from to make the selector value push fuel from the either tank?

For instance, when I switch from the rear to the front tank at the switch in the cab, a signal tells the selector value to push the front tank fuel through instead of the rear.

Does the ignition need to be in start or run to make the selector valve release the fuel?

I've got a big inline fuel filter right after the selector valve. I can see it fill up with fuel, so I'm some what confident that fuel is getting past the selector valve. The only thing past this filter is the blue dot vapor valve and another in line fuel filter (which I've verified not fuel is reach either).

 

[84-460-Project]

Thanks. I'll follow your advise and section the system off to find where the bad connection is.

Where did you put the fuel pressure regulator?

Its a brand new fuel tank selector. I triple checked the wiring, but i'll go through it again.

How many starts should I expect to prime an empty fuel line?

Where does the electric signal come from to make the selector value push fuel from the either tank?

For instance, when I switch from the rear to the front tank at the switch in the cab, a signal tells the selector value to push the front tank fuel through instead of the rear.

Does the ignition need to be in start or run to make the selector valve release the fuel?

I've got a big inline fuel filter right after the selector valve. I can see it fill up with fuel, so I'm some what confident that fuel is getting past the selector valve. The only thing past this filter is the blue dot vapor valve and another in line fuel filter (which I've verified not fuel is reach either).

How do I know if my inertial switch is bad or needs to be reset?

[ArdWrknTrk]

I replaced the oil pressure switch. I'm not sure what (or where the) the IIRC is. Is this in the loop for the fuel system?

How do I jumper the oil pressure switch?

IIRC means If I ReCall.

In other words 'I believe that's the oil pressure switch is below and beside the oil pressure sender (can) at the rear of the intake manifold.

You can jump the harness side plug with any loop of wire.

With a sock at each tank pickup and the stock filter you should be fine.

I know there is a fine screen in the vapor separator blue dot "T", but you say it's new.

Can I ask if you see any fuel flowing in the return line back at the selector valve while you have the pumps jumped and running?

 

[85lebaront2]

Thanks. I'll follow your advise and section the system off to find where the bad connection is.

Where did you put the fuel pressure regulator?

Its a brand new fuel tank selector. I triple checked the wiring, but i'll go through it again.

How many starts should I expect to prime an empty fuel line?

Where does the electric signal come from to make the selector value push fuel from the either tank?

For instance, when I switch from the rear to the front tank at the switch in the cab, a signal tells the selector value to push the front tank fuel through instead of the rear.

Does the ignition need to be in start or run to make the selector valve release the fuel?

I've got a big inline fuel filter right after the selector valve. I can see it fill up with fuel, so I'm some what confident that fuel is getting past the selector valve. The only thing past this filter is the blue dot vapor valve and another in line fuel filter (which I've verified not fuel is reach either).

First question, do you know how to read a wiring diagram? Not trying to be nasty, some people do not know how to read them. On the pressure regulator, Gary put his just before the carburetor.

Now to the other question, you said the new pump is a lot louder than the old one, are you sure it is the correct pump? A lot of places will try to sell you the mid 1985 through 1989 low pressure EFI pump which is way too high for a carbureted engine (ask Gary Lewis and I how we know). They are much noisier as they are gearotor pumps and the originals are centrifugal pumps.

The fact that you had fuel from the front tank, switched and nothing from the rear, then when you went back to the front, still nothing makes me suspect the selector valve isn't moving, it doesn't release the fuel, just connects the desired tank to the engine fuel lines. When you rerouted them, you didn't get them crossed did you? The larger line is supply, smaller is return, the valve has 6 ports two for each set of lines. The selector valve on yours should be like mine was and have 5 wires going to it. On front tank the brown with white wire should have power in run, in rear tank the orange wire should have power in run. The remaining 3 wires are the fuel gauge wires, yellow with white to the gauge, yellow with light blue hash, rear tank sender, dark blue with yellow, front tank sender.

On the switch mentioned, it is on the back of the engine, on a hex shaped fitting with the oil gauge sender (large dome with a single stud). It is a smaller switch with a molded shell that a two lead wire goes into. Here is a picture showing where the wiring runs, switch is visible as the black item where the red line goes on the back of the engine.