My front tank is sucking all the fuel from the rear to the front.
Also my front tank will run out of fuel while under a load and sometings without a load.
Does anyone know why my front tank is using the gas from the back tank before it uses gas from the front tank?
Why is the front tank running out of fuel when under a load and sometimes not?

I've replaced the switch valve and the fuel pump. Switch works and the guage works.

I am in need of the fuel line diagram. Does anyone know where I can get a diagram for my 1989 Ford F250 Duel tanks?

 

I have had these trucks for damn near 20 years now and have had every strange fuel problem imaginable between 3 trucks. I have found a couple of very common problems to be the chief sauspects.
1. Valve and resorvoir assy
2. Interior tank fuel pump and assicatied wiring (especially the connection at the firewall where the dash harness polugs into the frame harness).

If the front interior tank pump is not pumping due to either shot pump or crappy power to it, and the valve and resorvoir assy is screwed up (valves not properly seated) this phenomen will occur regularly (front fuel to back tank).Also, the same could work in reverse (back tank to front tank when back fuel tank interior pump doesn't work)
The fact that she is tumbling under load indicates that just the ligh pressure pump (one the rail) is working and the interior low pressure pump is not (frusatrating isn't it)!!!
I Just changed out the front tank, front sending unit with new pump anmd all lines , and a new high pressure frame rail pump just to find out my truck was doing the same thing after changing out all parts (I asked my mechanic if he checked the power to the interior front tank pump and he replied no). I ended up driving a 3000 mile round trip just on the back tank which is a 40 gallon tank so at least I didn't have to stop every hour for fuel (7.5 stroker gets about 10mpg)>

 

thankyou I might replace the front pump.But I"ll check the wiring connetions two make sure. the dual reservoir is new,but the front pump is a 7 year old new one right out of the box. lazy people had it before me and just used the rear one all the time.Although they both are working when I idle.It may be worth a shot. I thought it may be a vacum leak shoty fuel cap or cracked hose.Would maybe explain the siphioning that I have going on.

 

I found my problem today with the front tank pump not working...broken red wire in the middle of the harness (NOt at the connectors)...soldered new wireing in, heat shrunk it, taped up complete harness and put oin new 1/2: carflex (corrugated tube)...hopefully it won't happen again.

 

congrads hope u fixed it ain"t had A chance working on house

 

put a half tank through it today with no problems (other than paying through the nose for the fuel)>