On my '95 F-150 supercab flareside I'm sure I have a fuel transfer problem between the two tanks. Just need help with diagnosis. I need to look in the manual to see the exact tank sizes front to back but here's the problem...

Just filled both tanks last week. When the front tank is selected the truck runs fine however, the fuel sender does not work. It is on "E" 99.9% of the time but every once in a great while will peg above full then go back to "E". I also have a small fuel leak coming from the front tank somewhere when its full. This last tank I got a total of 40 miles out of a FULL front tank!!!!! The leak is not bad enough to drain that amount of fuel on the ground so not sure where its going. If it were transferring to the rear tank I would think the rear tank would leak no?

The rear tank (which I use most of the time) seems to run fine. Fuel gauge registers as it should, no fuel leaks or fuel smell & averages decent mileage for the 5.8 (most recently between 12-13 mpg city).

Am I looking at strictly a front tank module problem? Don't want to mess with both tanks if I don't have to.

Thanks guys!

 

It sounds as though you may need to verify it a little bit more. Maybe run the rear tank empty, fill the front, then drive on the front tank for a bit. After doing that, switch to the rear tank and see what the fuel level indicates. Then you would be positive about the transfer.

Whenever a tank is taking fuel when it's not being used, it will normally be the FDM in that tank. Example: Rear Tank takes fuel when front tank is being used = bad check valve in rear tank FDM.

I would first verify that the rear is taking fuel. If it is, you may have to go into each tank. The front to fix the leak and sending unit(could be external wiring too), and the rear to replace the pump. Sorry.

If it's not taking fuel, you may have a worse leak than you think. I dont know. Here is a FDM cutaway. When the pump is off, the check valves in it should prevent reverse flow through the pump and into the tank. Hope this helps!


Chris

 

Thanks Chris and I think you're right. The rear tank was definately overfilled & looks to be taking fuel when running on the front tank. Just really noticed this yesterday. Bummer! Looks like I'll be in for 2 new FDMs possibly and removing the bed...

 

Glad I could help! Sorry about the bad news.

The only "quicker" fix I can think of for the rear tank would be to score yourself an external check valve. It's the one Ford used back when there was a recall for this fuel transfer problem. Instead of replacing the pumps, they put a check valve on the line where it connects to the pump. Looks like this:


Don't know if it would even be worth it to try to get one though, if youre already doing the job, better to do it full on I suppose. It probably wouldnt be that much quicker either. Oh well.

Well good luck and I hope it works out well!

Chris

 

You have to remove the bed to work on the tanks? Can you just drop the tanks?

 

You can actually do it either way you like! Some guys prefer removing the bed. Some guys prefer dropping the tank from underneath. I dropped mine down because I had access to a lift and a transmission jack to hoist it up. If you dont have a lift, taking the bed off lets you work on the top side, but the bed bolts are known for breaking.

Chris

 

Thanks, I think dropping the tank will be easier.

 

Thats cool. I hope your work goes well for you. It's really just personal preference. Some are hardcore for one way or the other though.

Chris