My 78 f150 has duel tanks and I just got a new fuel pump and new lines put on. The rear tank had a collasped filler hose so they fixed that too. Now I went and put around 5 gal in the rear tank and tried to switch tanks and it shows that the rear tank is empty. The gage reads great on the mian tank. The truck keeps running so how can I figure out if it is really switching tanks.

Tim

 

If the fuel gauge is reading accurate on the main tank but reading empty on the rear tank (even though you know fuel is in there) it most likely is switching tanks, it sounds as though the sending unit in the rear tank is at fault, did it work before this most recent repair job? maybe they bumped the sending units wire loose while installing new fuel line.

 

I dont know if the tank worked before this repair. Whenever I put gas in the rear tank is spit it back out. So I never used the rear tank till now. I have owned the truck for 2 years. But kept it up norht in the barn & just used it to take crap to the dump. Now I want to start fixxing her up. It is just a cool old rust bucket, but not for long hopefully. Actually the cab is very solid but the box is shot.

Tim

 

I can hear the solinoid click with the key on when I turn the switch to the rear tank with my truck. There is no power to the solinoid when the main tank is on. Sounds like a bad sender though.

 

Where would I find the solinoid? That does sound like a good place to start. I do not hear any clicking.

Tim

 

On my 75 it is inside the frame rail on the drivers side before the rear wheel. But all you need to do is follow the fuel line from the engine back to where it splits to each tank and that is your silynoid. Sorry for the spelling.

 

When the dash fuel gauge is inaccurate, ppl automatically assume that the fuel sending unit in the tank is bad.

But...it's usually not the sending unit itself, it's the FLOAT on the sending unit that's defective.

The float is made from two pieces of copper soldered together.

The solder breaks down, gas seeps in, causing the float to slowly settle to the bottom of the tank.

The same float fits all cars/trucks from 1957 thru 1979.

COAZ9202B .. Fuel Sending Unit Float / Available from Ford.
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MSRP: $7.41 // FTEpartsguy.com price: $5.34.
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The sending unit gasket is the same 1960/79 (except for the in-cab tank)

COAF9276A .. Fuel Sending Unit Gasket

MSRP: $0.77 // FTEpartsguy.com price: $0.60
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On the sending units pickup tube is a plastic meshed filter screen.

Most people do not know it's there, so it rarely gets changed.

D1AZ9A011A .. Plastic Meshed Filter Screen

MSRP: $21.73 // FTEpartsguy.com price: $15.65.
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D5TZ9189B .. Fuel Tank Selector Valve and Solenoid Assy / Obsolete

Fits: 1975/79 F100/350 & E100/350 (Econoline).

This valve may look slightly different than the one originally used on 1978/79's (D8TZ9189A), because later on, Ford replaced it with the 1975/77 valve.

 

Thanks for all the info it will give me ideas andplaces to look.

Tim

 

On the 79 F150 4x4 I just bought for parts the selector is mounted in front of the rear tank on frame crosspiece. Also check the wiring harness that plugs into the sending unit before you go replacing the float or unit. On my 77 the ground wire for the harness was broken away so my guage didnt work. I believe it either Dennis Carpenter or Mac's that had the fuel selector for $91.