If you have the selector switched to the front tank the intank pump in the front tank will run as well as the one on the frame rail. If you are on the rear tank then you have the rear intank pump and frame rail pump working.
I should have said that this is on a 85' F250 7.5L 460. This is carburated so there is only intank fuel pumps, but I believe that only one should be working at a time. Could it either be a bad dash fuel selector switch or the fuel pump relay switch?
Thank You Very Much.
What exaclty is the problem you are having? Are they both running at the same time when the truck is running? You can check this better by getting a piece of garden hose about 4 feet long. Stick it down the filler tube and listen. Let me know if I can be more help.
For what it is worth, I have had nothing but trouble with fuel pumps etc. on my 86 F250 4x4. I put two new pumps in when the gauge quit. They have never worked right since. The rear tank pumps 5 PSI, the front pumps 1-3 sometimes. So I added a Carter Elect. Pump mounted on the frame with a Pres. Reg. ON/OFF Switch. Now I have little problem. I keep thinking I'm going to put about a 75 gal tank in the bed, and just remove all factory crap that has to do with fuel. Just run the Carter & Pres. Reg. 3/8" feed line and a 5/16" return line and the heck with all this trouble & cost. I think that your problem is in the switch over valve, That I believe is where some of my problems exist, and if I replace that at I think about $150 then I'll have over $500 in two pumps a valve and miscellanous hoses and stuff and if you add up the Carter pump, pres. reg, & Pres. gauge 6 bills is closer. Heck I could of bought a bed tank & gauge unit and saved alot of money. My point is this system has been junk and still is. I was working for a Ford Dealer in 84 and we worked on this system all the time. This must of been one of CHEVYS BETTER IDEAS, THAT FORD JUST COULDN'T SAY NO TO.