I'm looking for some reasons as to why my fuel mileage is different between tanks. I have a 94 F-150 4x4 with a 5.0L engine, it also has dual tanks. When using the front tank I get approx. 15-16MPG, when I switch to the rear tank I get approx. 8-9MPG. This is a huge difference to me and I would like to get it fixed. The suggestion has been that my rear fuel tank pump may not be providing enough pressure and is going bad. Before I drop the tank I thought I would ask here to get some ideas.

Thanks.

 

I have a similar problem with my 1994 5.0 F150. Mileage from the front to rear tanks was simillar to yours.

My problem was a bad sending unit in the rear tank - it would not accurately show the amount of fuel in the rear tank, so my mileage calculations were off. I've been told by other owners of similar trucks this is a common problem.

I've never repaired the problem - when the gage shows the rear tank is near the 1/2 way point, I just fill it up (the gage won't work when its more then 1/2 empty - just shows empty all the time).

Hope this helps.
Glenn

 

Only thing that comes to mind if it is on one tank, is the screen may be plugged that is on the end of the filter.

I'd swap the fuel filter too.

 

There was a recall on the fuel check valve. Something about fuel from one tank being returned to the other causing an overfill and overflowing out the gas cap. Something like this may account for the difference in fuel milage readings if performance is the same for both tanks.

 

No matter what the mialge should be exactly the same on both tanks. When I strated noticing I was getting worse milage on my fornt tank then on my rear I knew something was up.....sure enough I found out my front fuel pump was going bad and making a fuel crossflowe happen, when the front tank wa sin use some of the gas would then flow into the second tank, as soon as I replaced the front fuel pump everything was back to normal.

 

Flaresideglen I wouldn't use your fuel gauge even when it is working properly. I don't know of any gauge that reads proportional to fuel level. 3/4 tank on gauge might actually be 7/8 tank or 5/8 tank. Only way I know is to use the gallons at the pump when refilled.

 

It should not matter what the gauge read as long as you go by the miles driven divided by the gallons. That being said I just checked my rear tank and it was 12.5. Last week I got 17.8 on the front. I check my mileage by having both tanks full. It cannot be pushing fuel into the other tank since it is full and it would over flow. And I have not had any overflow problem.