Hi folks. 1988 f-150 lariat xlt, 302 auto.

Strange things are happening with my fuel. Let me try to reconstruct:

- Front tank got low, seemingly really fast (about 5mpg by my calculation) so I switched to the rear.
- Rear got low so I switched back to front and put in about 3.5 gallons.
- Front got low again really fast so I switched back to the rear so I wouldn't run out. When I did so the gauge went up to half a tank!

Is it possible that some fuel is running from the pressurized lines back up into the rear tank when the front one is in use?

I can't figure out why else I'd have such crap gas mileage. I have checked for leaks. There is a very slow leak beneath the drivers seat on the frame rail. But doesn't seem nearly serious enough to cause such bad mileage.

Is there any way to check the fuel levels in the tanks for sure without relying on the gauges? It would be nice to know how much is /actually/ in each one as a starting point.

Thanks for any help!

 

Both tanks are cross filling into each other. I'm not sure if the in tank pumps have check valves or not but it could be because of the switching valve on the frame behind the frame pump.

 

No check valves.

 

It isn't clear from your post, are you basing your calculations on the fuel gauge movement, or are you doing a complete fillup and dividing miles driven by gallons added?

-Kennon

 

Its a common problem for the tanks to cross fill one way or the other on this truck due the DFR dual function reservoir poppet valves not closing all the way. Usually as a result of the DFR being defective and as I have recently learned if the intank pumps are weak thus not supplying enough fuel to fully actuate and seat the valves.

 

Ford has(d) a recall for the problem you are experiencing, I've done hundreds of them and it comprises of adding inline check valves at the top of the tanks and replacing the fuel pressure regulator.

Run your VIN# on this link to see if the recall is still valid.

http://owner.ford.com/servlet/Conten...ge/RecallsPage

 

That would be for '90-'96. '87-'89 have a different system.

 

I have some of those check valves, they are hard to find and its a dealer only part. They want a fortune for them.

 

Don't remember the exact year models covered but 1987^ to ? were involved, he can find out by running his vin on the provided link.

 

Like I just said, '90-'96. His is an '88, it doesn't have check valves it has the DFR.