Fuel gauge reads

[Sorro71]

Driving home last night and switched from my1/4 full front tank to the full rear tank. At first the gauge read full, just past the F on the gauge. When I looked at the gauge a few minutes later it was pegged as far to the right as possible. So I switched back to the front tank and the gauge doesn't move it stays as far to the right as possible. It doesn't move back even when the truck is switched off. Since it has affected both tanks,do you think it most likely could be a faulty selector switch on the dash? Does a short circuit or an open circuit cause the gauge to peg as far to the right as possible? Has any one had any experience with gauge ******* as far right as possible no matter which tank is selected?

 

[DaveBen]

Sounds like a shorted (to ground) wire from the switch to the back tank. Maybe pinched somewhere along the frame going to the rear tank. These are a ***** to find... Good Luck!

 

[papadiesel]

multiple areas to check, no external ground, so selector switch, or in my case the connector ( 23.00) at the valve itself on the frame. Even when the selector makes noise (activating) it can be the connection as ground goes through it as well. Many hours, reading and testing went into this problem with mine. good articles on fuel reading problems here , far right reading means bad grounding

 

[OLDBULL8]

Maybe this will help.

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[madpogue]

What year truck? That determines one of two possible, opposite issues.

 

[papadiesel]

yes, the info posted above is excellent, but start with the simple things first, like wiggling the connector or plug and unplug at the selector vavle on the frame with key on, then it gets into senders, fuel antislosh on the back of the IC, selector switch, connector at sender, especially with a flatbed (more open environment) etc, the above info from OLDBULL8 has been reliable and trustworthy has been more consistent than many others on this subject! Went through all the symptoms and fixes with my 89 F250 dual tank system, Works like new with positive readings all the time now a year after the diagnostics and fixes

 

[Sorro71]

Wow, thanks for the great info guys. I'll start on it when I get home from work.

 

[franklin2]

The switch on the dash does not switch the sending units to the gauge. All the dash switch does is tell the valve on the frame to switch from one tank to the other. There is a electrical switch made into the valve on the frame that does the sending unit switching.

These valves like to fail, so if it is not moving, then the fuel gauge is not going to switch either.

 

[Sorro71]

What year truck? That determines one of two possible, opposite issues.

It was built late in 87. I've been told, that makes it an 88 model.

 

[papadiesel]

any number of what I mentioned does affect the fuel gauge, by book and by experience, not my first rodeo with the 6.9, 7.3 systems worked on since 1988 on these guys

 

[laserjock]

Pegged to F is a broken connection from the sender. If both tanks are doing it it's between the gauge and the selector valve.

 

[Sorro71]

Think I've found the problem. I have fuel weeping from the selector valves plastic housing, my guess is something inside is about to let go. Are these still available from Ford or is there a good aftermarket one available. It has the quick connect fittings. I'm going to search the net and see what I can find.

 

[pelky350]

Mine does something similar however once the tanks are low like below 1/8th tank the needle just bounces around from 1/8th to full until the tank is empty, maybe we have similar issues I'll be checking back at this post!

 

[OLDBULL8]

Think I've found the problem. I have fuel weeping from the selector valves plastic housing, my guess is something inside is about to let go. Are these still available from Ford or is there a good aftermarket one available. It has the quick connect fittings. I'm going to search the net and see what I can find.

The FSV (Fuel Selector Valve) is still available from Ford, last I new, the price was $260 US. The PSD's use an updated version, but don't know if the fittings and mount is the same.
You can easily take your's apart and check it out, I used a 1/4" drill to just drill enough to cut the crimp off, then punch out the rest. Use #6 sheet metal screws to put it back together, drill out the one half so the screws slide thru.

EDIT: I don't think the body of the FSV is leaking, the quick connects have an O'ring in them that can leak from old age.

 

[Sorro71]

EDIT: I don't think the body of the FSV is leaking, the quick connects have an O'ring in them that can leak from old age.

I thought that to. It s definitely leaking from the body. When the truck is running I can dry off the valve and I can see exactly where its weeping out of the body. I'll try and get a picture this afternoon. Ford sold the PSD's over here for a while so I'll see what Ford wants for the valve over here. I best be sitting down for the price.