Fuel Selector Valve Overhaul

[david85]

The fuel selector valve (FSV) failed in my truck a couple years ago. I was able to repair it by taking apart two valve assemblies and making one good unit. In doing so, I thought it might be possible to make a good valve out of the remaining parts. Feedback from folks here told me that the aftermarket valves aren't exactly reliable, so why not try fixing the OEM? Never know if you don't try, right?

I'll have to post several times to go through all the photos and components, so bear with me.

First up is the valve hardware. The design is very simple and uses many off the shelf components that you can still source today. What's better, there are no carbon steel parts. Everything is made from stainless steel, fuel resistant plastic, or fuel resistant O-rings (likely viton).

The white seals shown here are from McMaster Carr, since the originals had a few tears in them. The E-clips are also sourced from the same place, since one of them had rusted apart.

You must be registered for see images attach

Here's the valve holder, which is made of plastic. These are pretty much irreplaceable, unless you're handy with a 3D printer (and I'm not). These need to be clocked correctly to align with the fuel line ports.

You must be registered for see images attach

Up next, the sub assemblies are put together. The blue seal is original. White is new, and the green is extra I had from an A/C O-ring kit. The part under my finger is what actually moves to connect either the front tank or the rear tank. Note that there are in fact two identical valve sub assemblies like this for each complete fuel selector valve assembly. I'm only showing one here since the other is the same.

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

What's the spring for, you may ask? This is what applies pressure for the seal to actually make the tank connections. With the stem plunged in, one tank is connected. With the stem retracted all the way, the other tank is connected. The spring means that the motor cannot apply too much force to the seal. It also means the distance of travel doesn't have to be as precise. And in this case, less precise means more reliable (and cheaper).

This means three likely failure modes:

1. Fail in the last known position. Not much issue here, since you can continue using the tank that was already selected. The motor uses a screw actuator, so it won't likely move unless the motor is powered. You won't be able to switch tanks, but you can still keep driving the truck using the one tank.

2. If the mechanism breaks, the valve stem may relax to the center position (or if the motor fails mid-travel). If this happens, it can block off both tanks, and immobilize the vehicle.This type of failure is relatively unlikely, because of how the mechanism is built. More on that later.

3. Partial failure. This is what happens when one of the two valves gets stuck. One valve is for fuel supply, while the other is return return to tank. So this is how you get into a situation of overflowing one of the tanks while driving. This is usually caused by a physical object getting stuck in the valve. Although a drive mechanism failure could also cause it, depending on what failed.

Up next: Installing the valve sub assembly into the FSV case.

 

[david85]

Here's the valve components put together. You can see the side port and the end port openings. These align with the ports on the main outer case.

You must be registered for see images attach

You must be registered for see images attach

Remember that side port? Here's the hole it must align with on the outer case. If you clock this incorrectly, one of the ports will be permanently blocked, except for a small trace of leakage.

You must be registered for see images attach

Time to install the valve into the case. Note the other valve is already installed.

You must be registered for see images attach

Use a touch of grease to help on this part. But also watch out for pinching the upper O-ring. If the grease isn't enough to get that O-ring seated, you can use a small, but smooth utensil, like the side of a dull scriber to help get it in while applying pressure.

You must be registered for see images attach

 

[david85]

Once both valves are fully installed, it should look like this:

You must be registered for see images attach

You can partially test the valve by pushing down on the stem and seeing if it springs back to the middle position Don't try pulling up yet, or it will pop out of the case.

The retainers can be installed using a socket wrench that matches in inner diameter of the recess. Removal is also fairly simple if you have a sharp, 90 degree pick. Avoid trying to install and remove them too many times, since it will chew up the plastic.

You must be registered for see images attach

At this point you can test each valve using air pressure. I suggest not using full shop air, since the plastic case is probably not rated for that much pressure. If it seals, this part is finished and ready to go. Up next, the mechanism.

 

[Clb]

@snicklas
Can you add this to the tech section?

 

[david85]

If this were made today, there would probably be a software integrated chip on the FSV itself, and a brushless DC motor to actuate it. But since this was likely designed in the 70s, Ford had to use mechanical components to accomplish the task.

First, is the linear actuator. The jack screw appears to be brass, while the rest is made of a fuel resistant plastic. I don't know what the plastic is actually rated for, but if it's not brittle after 40 years exposed to fuel, I think it's earned the title.

You must be registered for see images attach

Believe it or not, this is the "computer" of the assembly. And I honestly can't find much wrong with the design. Someone put some thought into this.

The spring loaded black arms on the side limit the travel of the brass jack screw. The black rectangle piece to the side is a torque limiting coupler for the electric motor. More on that later.

Below, we see one of the arms is now extended, meaning the jack screw has reached the limit of travel.

You must be registered for see images attach

Now the other arm is extended, having reached the other limit of travel. Also notice the torque limiter is much closer. If it wasn't for the torque limiter, the mechanism would probably break, since the motor has no way to "know" how close it is to the end travel. Once it reaches full travel, power is cut, but momentum keeps it moving for another half second, or so. This torque limiter slips to prevent shock loading anything. Crude? Yes. Does it work well? Apparently.

You must be registered for see images attach

Here's a better view of that torque limiter (black rectangle) taken apart. See those metal bands on either side of the hole for the motor shaft? Those are actually leaf springs. The lower round piece fits between the leaves under tension. Look closely, and you can see two flats molded into the side of the insert. When the flats are against the springs, torque is transmitted. If there is too much load, the springs spread outward and the coupling slips, until torque load is low enough to grab again. Not something that should be spinning all day, but it works well for pulse duty, which is really all this is.

You must be registered for see images attach

Hopefully you can see how it's assembled. Black plastic doesn't show up too easily on camera.

You must be registered for see images attach

 

[david85]

Alright, so what are those other brass contraptions on the sides of this actuator?

Those are the contacts for the internal switches. There's a switch on each side of the actuator that change states depending on where the switch is along it's range of travel. One set connects power to drive and reverse the motor. The other is used to make and break the connection for your fuel gauge. When switching tanks, the FSV not only changes the fuel supply and return circuit, but it also changes which tank sends a fuel level signal to your fuel gauge.

This also means that a faulty fuel gauge could potentially be from a bad FSV. This can be useful knowledge if troubleshooting problems that may not seem related at first.

You must be registered for see images attach

Inside the other half of the case, we can see the motor in the bottom, and two sets of slider contacts on either side of the central housing. Note the two diodes on this side. This side is the switch for the electric motor.

You must be registered for see images attach

The other board does three things:

1. Supplies power to the motor

2. Provides pins to the chassis connector outside (this is where wires pass through the case).

3. Switches between fuel tank sending units for the fuel gauge.

Looking below, you can see the board for the motor simply slots into the inner case. The other is retained using some metal tabs that slot into the case. It can be tricky to snag the far end, but a steel hook should be able to pull them out.

You must be registered for see images attach

The motor mounting plate is retained by a steel clip that bites into two of the plastic studs. No pictures of the clips here, but you can see the studs.

To remove the motor and boards, remove the boards first, then the motor comes out with them. These wires are a little delicate, so be careful here.

You must be registered for see images attach

Whats interesting about the pin connector board is that Ford provided for a synthetic rubber gasket to help seal it to the inside of the case. This rubber seemed to hold up well in the diesel FSV I pulled apart. However, the gasser valve had seals that hardened over time. After nearly 40 years, I can't be too critical.

You must be registered for see images attach

 

[david85]

Ok, time to start the final assembly.

Here we see the actuator installed on the valve side of the case. This is retained only be E-Clips. The spare FSV that found had one of these E-Clips rusted apart. I'm still not sure if it was made of Stainless, or carbon steel, but need to be replaced. The spare FSV also had evidence of fuel and water sitting inside of it for a very long time.

I've also reinstalled the original gasket. Cork, rubber sheet or even RTV would probably work if the original is too far gone.

Remember what I said earlier about the valve naturally resting in the middle position? Here's what it looks like. Again, all ports are blocked off in this position.

You must be registered for see images attach

Here I'm pushing the actuator down, to force the valves to the plunge position. They might feel a little sticky but some assembly grease will prevent this. And if all goes well, the seals will never be dry once installed in the truck.

You must be registered for see images attach

Here I'm doing my best to pull the valves to the retracted position, with only one free hand.

You must be registered for see images attach

Alright, the two halves are ready for assembly.

A few things to pay attention to here.

1. Make sure all E-Clips and plastic retainers are installed. Note the motor fasteners are now installed. The linear actuator has 4 E-Clips: two on top, which are visible, and two more below, which are hidden in this view.

2. Spring loaded contacts on either side of the actuator will have to be gently pinched together in order to fit into the case. I also like to apply a light dab of anti-corrosion grease in situations like this. Some folks don't like that, but I do, so I use it on most of my electrical connectors.

3. The motor shaft has a flat side to engage the torque limiter coupling. Zoom in on the photo and you should be able to see this. You'll have to align the motor and coupler while putting the two halves together. Be patient and don't force anything. These parts are 4 decades old.

You must be registered for see images attach

 

[IDIBRONCO]

This is a great thread!

 

[david85]

Almost there. The assembly is together. Note the hairline gap between the two halves. This is from the gasket still having some compression flex in it. Ideally, I would use some very small stainless nuts and bolts to complete the final assembly, but you can use rivets or self tapping screws. If you're in the rust belt, stainless steel is highly recommended. Just realize the plastic is old, so anything that is too thick or has a counter sunk head might crack the ears.

The two snap tabs on the sides are only for initial assembly. Chances are another technician would have been responsible for installing the rivets at the factory.

You must be registered for see images attach

It's also interesting to note that everything you see here would have been made entirely by hand, back in the day. Which is why it's possible to rebuild it by hand four decades later. Finicky, sure. But not much worse than rebuilding a carb or matching and pop-testing your fuel injectors.

Cleanliness is important here, but keep in mind there is still the main filter downstream of this. In other words, don't be too scared to take this on. Worst that can happen is you have to buy a new one anyway.

You must be registered for see images attach

 

[david85]

What failed in my original FSV?

Looking at this, it appears to be the motor, itself. The rear housing is plastic and shows signs of melting. The windings were charred as well. Look close, and you can see the rear shaft bearing is no longer centered because the plastic melted. More clues at the time were the fuse kept popping instantly and the fuel gauge stopped working whenever I tried switching tanks, so I knew there was an electrical short somewhere.

You must be registered for see images attach

Side view of the OEM Motor:

You must be registered for see images attach

And the Face. The mounting bolt pattern is standard, and so is the motor. This means the original mounting plate and screws can be swapped to the new motor. I think some kind of blue loctite was used at the factory, so I did as well. The only trick was finding the correct motor since there are many different types in this size range. This would have probably been used in hundreds of different kids toys back in the day, from RC cars to whatever else. Made in what was then non-communist Hong Kong, a different world for sure.

You must be registered for see images attach

Any complaints about the design? Well, yes. Both FSVs showed evidence of fuel and/or water intrusion. This probably isn't avoidable, since no seal is perfect. The electrical connector faces the road when it's installed in the truck, so in theory water intrusion there is somewhat mitigated. The FSV is also tilted toward the motor end, so any fluid intrusion will collect there first. I suspect fuel alone might not matter that much, since its not conductive or corrosive. So anything that gets past the stem seals (blue O-rings) may not matter (at least, not right away). However, water or fuel intrusion is still not ideal. I'm toying with the idea of adding a small pinhole at the bottom corner for drainage but haven't tried it yet. I'll probably think about it for a few more years, then decide.

Besides the 100% reliance on the seals with no provision for egress of contaminants, I actually think its a pretty good design. You can tell it was made by hand and that means we can still fix them now.

Did I save money compared to buying one from amazon? Meh, if I did, it wasn't by much. The first motor I bought was too large, and McMaster charges minimum $20 shipping on small items. Although, their website is beyond excellent for their attention to detail. Seriously, even the E-Clips had CAD drawings for the exact dimensions. It's a far cry from Fleabay or Amazon.

Here's the parts list I used:

Motor: RS-380 type 12V motor. Should be plentiful at any hobby supply. Be warned, I had to trim the shaft length, and then grind the flat myself. I tried to find an exact match but was unable to

The O-Rings and E-Clips were ordered from McMaster Carr. Here's the part numbers:

You must be registered for see images attach

Hope it helps. Good luck!

 

[The_Josh_Bear]

Wow, excellent work and write-up! Thank you!

 

[Kizer]

Well done Sir.

 

[snicklas]

@snicklas
Can you add this to the tech section?

Yes I will. I’ll leave it here for a couple days, that way if he needs to make any updates, he can.

 

[Clb]

Op
Once you have everything figured out, you can submit it to a mod for inclusion in the tech 101 stickies.
I forget how tho...

 

[david85]

Yes I will. I’ll leave it here for a couple days, that way if he needs to make any updates, he can.

Should be good to go now.

I just finished one last editing pass. A made few grammar corrections and clarified how the fuel gauge can behave when the FSV malfunctions (in some cases, the fuse will pop and the gauge goes dead when trying to switch tanks).