Hello, i am looking at an 89 f250 with dual tanks and it has the following issue...

The truck wont run on the front tank and when running on the rear tank the fulel returns to the front tank and overflows the front. I suspect the front tank low pressure fuel pump is bad but since the fuel is returning to the front when running off the rear does that mean the mechanical fuel selector valve is bad as well? Also, if i just wanted to run off the rear tank could i bypass the selector valve altogether by connecting the rear tank lines (supply and return) directly to the engine lines (supply and return) at the selector valve?

Thanks in advance for your help. I hope to buy this truck which looks and runs great other than this fuel issue and become an active and productive member of this forum!

Don

 

welcome to FTE.
you are correct in your diagnosis of the problem, the front in tank pump is bad.
if i remember correctly the "selector valve" is built into the fuel pumps on the later trucks and not an actual valve mounted to the frame like on the older trucks.

 

My 97 has the selector valve on the frame.

 

because your 97 diesel does not electric fuel pumps in the tanks. you have a mechanical pump on the engine with a selector valve on the frame.

 

Tom, if the 89 doesn't have the separate "selector valve" mounted to the frame then I am wondering why/how the return fuel is going to the front tank instead of the rear tank? I thought the front tank fuel pump not working was why the selector valve was not properly working to change the return routing... not sure I am explaining this well but if I the 89 doesn't have the separate selector valve I am thinking a bad front tank pump would just have the effect of making the front tank not work but wouldn't impact the rear tank operation like it is...
Thanks all for the help! Don

 

like i said, i am not sure on the gas rigs because i only have diesels. inside the in tank pump is a valve. this controls where the fuel goes. when on rear tank, the rear pump runs and the front tank return line valve is closed. when on front tank, the rear pump return line valve is closed. fuel crossover is an indication of the front tank pump needing replacing.

i know this is how it works with the newer trucks, but not sure if the pre 92 trucks are the same.

if you can hang on until tomorrow when the regular crowd gets back from their weekend playing, someone more knowledgeable on these systems will jump in and tell you i am rite, or just a senile old fart

 

Thanks Tom, I can certainly hang on until tomorrow and I very much appreciate your help!

If it turns out that there is a frame mounted fuel tank selector valve I would be interested in hearing opinions on possibly bypassing the valve and running only off the rear tank. Anyone see issues with that? Has anyone done something similar and know where I might get the connector mates rather than cutting the lines and putting some other type of in line splice in to mate the rear fuel tank lines to the lines going to the engine. Thanks again in advance for your help!

 

I am also experiencing some issues on my 96' F-350 7.5l with the dual tanks. The front tanks not working and the rear's fuel gauge is all over the place along with what I think is fuel starvation with ample fuel in tank. Looked for external fuel diverter/selector valve, not present. Parts store has in tank fuel pump w/o fuel level sender as part of a module, I'm assuming this is correct to my application. I'm getting hesitation and what seemed like ridiculous mileage until I find the rears still has ample fuel. This rig is newly bought and I fill like an idiot for not finding this at inspection and test driving. I new the front tank wasn't working but I have a 90' E-350 Club Wagon with dual tanks, same thing but absolutely different results. In the van the front side tanks internal pump went out, no worries ran off the rear w/o a problem whatsoever. On the van it does have an external selector valve which I believe may isolate the tanks from effecting one another. This is a working theory though and I could be wrong, or way off. Anyways I'm not sure what is really going on with this 97' F-350...

 

I'm not a mechanic, I have symptoms and issues no real good answers or solutions. If I find any other sources in my active and current searches I will share asap. When I was young I used to know many an older mechanic that would hear of a problem with my vehicle or anyone's vehicle and tell you what it was. They would get to one or maybe two possible problems with a 'check this then it's this' even with all the computer, fuel injection, sensors, and other modern emission crap. These guys hardly needed another computer, or scope, or analyzer. Now I go to a garage and mechanics are bewildered or saying well it's putting off this n that code and it could be this or that. I actually get my vehicles back halfassed or get warned that this will take a lot of hours and be very expensive, other times they find one or two things that are needed but do not resolve the real problem completely. This has happened with Ford dealership mechanics at several dealerships. Maddening.

 

Idk if anyone cares anymore but i thought id add this... been workn on a 88 witj dual tanks, pump and filter frame mounted. The black canister just behind the pump is the selector valve. These trucks have 3 ! Fuel pumps, one in each tank then the frame (booster) pump. There are no wires connected to said valve and works as follows.. has diaphragms and a mechanical valve that switches via fuel pressure from whichever tank is operating. They do jam up, are not cheap. I removed and blew compressed air with a rubber nosed blow gun in the ports and it unstuck. The side wth 4 ports goes to tanks wth the larger tube being the feed an smaller return..

 

I did read that a fuel resovior from a mid to late 80'S bronco II and posibly a ranger will fit inline, has no moving parts, and you just eliminate the 2 unused lines from tank no longer in use..may want to unhook tank fuel pump power as it will still pump if dash switch is flipped to the other tank

 

Mike, appreciate your added info. I would modify what you have said just slightly... the frame mounted fuel pump is not a booster pump. It is a high pressure pump that feeds the engine from the reservoir of fuel in the "black canister" as you call it. This reservoir is fed by the low pressure pumps in each tank. I have heard of folks replacing this with a single tank reservoir as you have indicated. This would be unacceptable to me as I would then get less miles between gas stops than I get on my Harley :-) I do have the 460 cubic inch beast that has an insatiable appetite for fossil juice... Cheers!