I just bought my first Ford truck at auction last month and i have a few questions. It is a 1987 F-250 super cab with the 5.8 351w engine it also has the dual tank feature on it. My problem is this my fuel gauge always stays on full no matter how much fuel is in the tank. The only time it moves is when it is almost empty and than it swings from empty to full when i press on the gas. The only way that i know that it is near empty is because when this happened i went and filled my tank and it took 16 gallons to fill. Is this a common problem with these trucks and if it is does anyone know what i need to fix it?

 

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If it only does this in one tank only, could be a sticky float in the tank. If it does it no matter what tank you switch to, could be an electrical problem in the guage or switch. My '94 XLT 4wd had a similar problem (but only with the rear tank) and the dealer replaced the pump assy in the tank. I have always paid attention to keeping the tanks in this truck reasonably full, and switching tanks back and forth every 1/4-tank or so. Fuel recipes vary slightly from season to season here. Some people let a tank run dry, and only use the second one. Maybe they think it's economical or something. The dry one will build up condensation moisture, especially with corn-squeezings in the last fuel recipe. One of my neighbors did this for years ('92 F150 2wd with all the bells and whistles) and it finally required the replacement of his unused tank (small rust holes had formed all over it) and the pump, probably seized up from rust also.
Good luck with yours. At least you have two tanks. When the one is running out, the engine will let you know in a Hong-Kong second. But the switch will kick in the other tank, and the pump will refill the injectors and off you go with vey little loss of speed. At least mine did on the freeway, took me a second to guess what the problem was, another second to switch tanks, and the truck never lost more than 10mph or so. Very fortunate, as this happened on the freeway in heavy traffic. Kind of impressed with the recovery the system made after being allowed to run out of fuel in the operational tank.

 

their is a small black box under the dash on most fords that hooks up to the fuel gauge.It is called a flex fuel module and ford has a problem with these going.if your gauge bounces around it probably is that part.

 

i have the same problem, but this is the first time ive heard of that flex fuel module. where is it at under the dash, and is there any way to test it to make sure that it is truly that that is going out?

 

I have a simular problem on my 87 F 250 ext cab. Mine is a Diesel and a duel tank. The front tank stays over the full mark till it has (?) 1/4 tank. then bounces from full to 1/4 tank. The rear tank acts more like it should but I somtimes wonder about it.

 

yeah, thats exactly it, and i really dont want to put in new fuel pump assemblies (as this is happening in both tanks) and im poor college student......haha, so for now i just deal with it, but if that FFM can fix it, im down to try, just need to know where to look

 

my truck did the same thing and i replaced the sending units and it was fixed. the contacts on the float assembly were worn away so bad that it caused the gauge to float around and then peg past full

 

If your truck is not setup to burn Flex Fuels then you will not have the flex fuel module to interpret the different types of fuel senders.

Flex Fuels = compressed natural gas (CNG), propane, and ethanol/methanol-based fuel systems

The term 'flex fuel' (FF) describes the ability of the powertrain control module (PCM) to adjust fuel control and timing to match the percentage of ethanol/methanol (alcohol) content in the fuel.

 

thanks for the info subford, like i said, i hadnt even heard of anything like that, especially on these older trucks.