1984 250 460 dual tank- trouble priming fuel lines

[Gary Lewis]

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).

I put the fuel pressure regulator just after the hot fuel "T" as you called it. However, were I to do it over again I'd replace the T with a return-style regulator.

There are two styles of regulator - a "dead-head" unit that goes on the end of a line and just lets enough gas through to supply the pressure. Or a "return-style" unit that diverts fuel back to the tank to keep the pressure at the set point. So, if you used one of those you wouldn't need the T.

But, right now you have no pressure. And the truck may run fine with your pumps. So worry about that if and when it happens.

I see Bill has responded, so I'll not address the other things so as to not overwhelm you.

[84-460-Project]

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.

Inertia switch is just to the passenger side of the floor hump on the heater duct, it has two yellow wires, but if either pump is running it is closed.

With the key on, and nothing running (including the pumps, they should not run until the engine is cranked) you should be able to hear a pretty solid thump from the selector valve when you change tanks with the switch, when the switch is moved to the front tank position, you should also be able to hear the tank selector relay (on the firewall, underhood) click closed. The fuel pump relay will only close with oil pressure operating the switch.

Thanks for the details. Your wiring diagram questions is a fair one, and yes I'm able to read and follow it. I validated the wiring setup matches (the instructions in the box, the service manual and the diagrams in this thread)

UPDATE: Today I disconnected the fuel lines from the selector valve to take it out of the equation.

I left the wiring hooked up to selector valve.

I connect the fuel sending line (3/8) and he return line (5/16) to the rear tank.

I flipped the fuel tank switch to rear and cranked the motor (3) times.

The carb got fuel and the truck started and kept an idel. It took less than 6 sec to prime the lines and get fuel to the carb.

I thought about how I hooked the fuel tank lines to the selector valve to ensure I didn't cross the lines. They looked correct. The rear tank fed into the bottom and the front fed into the top. The sending line is 3/8s and the return is 5/16s, so I'm confident I didn't switch them around.

I'm wondering if the fuel line diagram that came with the selector valve is backwards? Maybe I can test the selector while its disconnected. I'll leave the wiring connected and alternate between the rear and forward positions from the fuel tank switch in the cab. I'll blow some air through the tank side ports to see which one is open and which one is closed. I wonder if a check valve is stuck.

[85lebaront2]

Thanks for the details. Your wiring diagram questions is a fair one, and yes I'm able to read and follow it. I validated the wiring setup matches (the instructions in the box, the service manual and the diagrams in this thread)

UPDATE: Today I disconnected the fuel lines from the selector valve to take it out of the equation.

I left the wiring hooked up to selector valve.

I connect the fuel sending line (3/8) and he return line (5/16) to the rear tank.

I flipped the fuel tank switch to rear and cranked the motor (3) times.

The carb got fuel and the truck started and kept an idel. It took less than 6 sec to prime the lines and get fuel to the carb.

I thought about how I hooked the fuel tank lines to the selector valve to ensure I didn't cross the lines. They looked correct. The rear tank fed into the bottom and the front fed into the top. The sending line is 3/8s and the return is 5/16s, so I'm confident I didn't switch them around.

I'm wondering if the fuel line diagram that came with the selector valve is backwards? Maybe I can test the selector while its disconnected. I'll leave the wiring connected and alternate between the rear and forward positions from the fuel tank switch in the cab. I'll blow some air through the tank side ports to see which one is open and which one is closed. I wonder if a check valve is stuck.

There are no check valves that I ever found on mine. The valve piping sounds correct from what I remember on mine, I seem to recall the rear tank went straight in to the valve and the front went in the top with the lines to the engine coming off the front.

What you might want to do is take the valve loose, I know it's not fun and make sure it is moving to both positions and connecting the ports properly. It is the correct 6 port motor operated valve I hope, if it is a "universal" aftermarket one it is going to give you problems as it will not switch the gauge senders. Be glad yours is an 84, the 86 system Ford did away with the tank selector relay and everything is done in the valve and switch. As a result the valve won't move unless you are cranking the engine or it is running.

[Gary Lewis]

Thanks for the details. Your wiring diagram questions is a fair one, and yes I'm able to read and follow it. I validated the wiring setup matches (the instructions in the box, the service manual and the diagrams in this thread)

UPDATE: Today I disconnected the fuel lines from the selector valve to take it out of the equation.

I left the wiring hooked up to selector valve.

I connect the fuel sending line (3/8) and he return line (5/16) to the rear tank.

I flipped the fuel tank switch to rear and cranked the motor (3) times.

The carb got fuel and the truck started and kept an idel. It took less than 6 sec to prime the lines and get fuel to the carb.

I thought about how I hooked the fuel tank lines to the selector valve to ensure I didn't cross the lines. They looked correct. The rear tank fed into the bottom and the front fed into the top. The sending line is 3/8s and the return is 5/16s, so I'm confident I didn't switch them around.

I'm wondering if the fuel line diagram that came with the selector valve is backwards? Maybe I can test the selector while its disconnected. I'll leave the wiring connected and alternate between the rear and forward positions from the fuel tank switch in the cab. I'll blow some air through the tank side ports to see which one is open and which one is closed. I wonder if a check valve is stuck.

As Jim/ArdWrknTrk says, progress is good. And you are making progress.

It does look like the valve is the issue, which make sense as it was the only common thing that could keep fuel from the carb if the pumps are running.

As Bill said, you need to verify that the valve works and which way it goes when it does work.

[84-460-Project]

As Jim/ArdWrknTrk says, progress is good. And you are making progress.

It does look like the valve is the issue, which make sense as it was the only common thing that could keep fuel from the carb if the pumps are running.

As Bill said, you need to verify that the valve works and which way it goes when it does work.

Thanks so much for the help. After tearing everything down and starting over - we got it to run.

I tested the valve selector with an airhose to validate which ports opened in when the front is selected, and which is opened in when the rear is selected. Connected and tested each tank separately, put a clear inline fuel filter on the fuel tank side and one right at the carb, and everything worked out.

It took no more than (3) starts to prime the lines.

It a strong possibility I connected the tanks to the wrong selector valve.

Lessened learned.

Now we need to time and tune.

[Gary Lewis]

Thanks so much for the help. After tearing everything down and starting over - we got it to run.

I tested the valve selector with an airhose to validate which ports opened in when the front is selected, and which is opened in when the rear is selected. Connected and tested each tank separately, put a clear inline fuel filter on the fuel tank side and one right at the carb, and everything worked out.

It took no more than (3) starts to prime the lines.

It a strong possibility I connected the tanks to the wrong selector valve.

Lessened learned.

Now we need to time and tune.

Yippee!!!

Glad you got it going. One layer of the onion peeled, more to go.

[85lebaront2]

Thanks so much for the help. After tearing everything down and starting over - we got it to run.

I tested the valve selector with an airhose to validate which ports opened in when the front is selected, and which is opened in when the rear is selected. Connected and tested each tank separately, put a clear inline fuel filter on the fuel tank side and one right at the carb, and everything worked out.

It took no more than (3) starts to prime the lines.

It a strong possibility I connected the tanks to the wrong selector valve.

Lessened learned.

Now we need to time and tune.

Sounds great! The hot fuel package can be a nightmare the first time you have to deal with it. Working properly it is great.

One suggestion from someone who has dealt with it's idiosyncrasies, you might want to add a "priming button" that will put 12V to the wire on the starter relay if the truck isn't going to be driven frequently. I found if mine sat for a week or more without being started it took a bit of cranking to fill the carburetor to the point it would run.

[Gary Lewis]

One suggestion from someone who has dealt with it's idiosyncrasies, you might want to add a "priming button" that will put 12V to the wire on the starter relay if the truck isn't going to be driven frequently. I found if mine sat for a week or more without being started it took a bit of cranking to fill the carburetor to the point it would run.

If I weren't installing EFI on Big Blue I'd do that, for sure.