The in-tank fuel pump on the rear tank on my '89 F-250 has started producing a high pitched whine when the rear tank is selected. Whine goes away when I switch to the front tank. Is this an indication that the tank fuel pump is about to go South?

Given the age of the truck....and if it's the original pump...then yes, it's probably getting tired.

Thanks Duncan. I'm sure it is. I replaced the pump on the fuel rail last summer. It looked to be original.

Typically, when they get noisy, they are about done...

Pretty sure that is what that indicates from past experiences.

Thank you, Roger.

could be you ran over your mother in law...... She's back there making the high pitched whine.......

dustybumpers said:

could be you ran over your mother in law...... She's back there making the high pitched whine.......

Click to expand...

I plead the 5th!

My Gf's been whining a bit here lately. You think she's about done ?

They're never "done"

Okay, back to the task at hand....... I switched fuel pumps today and crawled under the truck to locate the source of the noise. The noise appears to be coming from the mechanical switching valve...........This was replaced last summer with a new Ford valve. Is it possible that the fuel pump is transferring the noise to the switching valve?

I was prepared to pay $200 for a Motorcraft fuel pump(I only want to do this job once) but held off. I don't want to buy the pump if it doesn't need replaced.

Unless the switching valve is allowing fuel to bypass, I can't see how it could make any noise... Are you certain the high pressure pump isn't the culprit?

The fuel pump on the frame rail is about 2 feet away from the switching valve. If I get up close to the switching valve, and move toward the fuel pump, the noise seems to lessen in volume. I can't feel any vibration on the fuel pump when I put my hand on the pump, also.

I will put a screwdriver on both the pump and the valve, and listen to see if I can better isolate the noise.

There is nothing in the switching valve to make noise.

I agree. But that's where the noise appears to be coming from. That's why I asked if the noise might be transferring from the pump to the switching valve.

Try loosening the main pump out of the frame, my bet is it's doing an echo effect, and traveling down the frame.

You could also have a bad lift pump. If you have more than 1/4 tank of gas, the weight of the gas will "push" itself out of the tank, making the lift pump scream. truck will run out of gas at 1/4 tank tho. This only helps if the guage is correct.

Try taking the lines off the transfer reserve.
Disable the main pump at the pump electrically
Aim the line at a can, and have someone cycle the key for each tank.

This will tell you if the lift pump is working.

Be carefull tho, the nylon lines are brittle, I pinched a hole in mine doing this and didn't realize it until I was out on the road and changed tanks/
Gas does a pretty good job of removing undercoating....

I have been lucky, my lines have all been in good shape, even on the 86... I agree though, the noise has to be travelling from somewhere, it really can't be from the switch itself. You could bypass the switch using steel line inserted into the fuel lines to see if the noise changes. A 3-4" chunk will do. One is 3/8", the other is 5/16". The o=rings int he fittings will seal up to the steel lines. Expect the plastic clips to break though...

Thanks for the info, Roger and Charlie. Won't have time to take a closer look until next week.

Plastic clips are only fuel filter clips, so no big deal there.
If you push them out with a screwdriver from the bottom, instead of prying them out from under the wedge part, they usually don't break

Yes, the clips are easy to get. They tend to get brittle over time. I have had them break even pushing from below the clip, not the wedge.