Changing the tank selector valve
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
elbowgrease,
Have you driven the truck for a couple of days on the front tank?
Does the fuel go down but the gauge stays reading full?
When the switch goes to the other tank, the fuel gauge connection is the last thing to engage.
Have you driven the truck for a couple of days on the front tank?
Does the fuel go down but the gauge stays reading full?
When the switch goes to the other tank, the fuel gauge connection is the last thing to engage.
New User
Joined: Jun 2006
Posts: 7
Likes: 0
Yes. I drove the truck for a couple of days with the switch on front. The gauge wasn't going down. I was thinking that the sender or gauge was bad, but initially it didn't occur to me that anything but those could be defective.
All at once, it hit me that maybe I was actually draining the rear tank. I threw the switch to the rear, and the guage dropped near zero. I didn't totally panic because I know the rear sender gives readings all over the place once I drive on the rear tank for more than 5 gallons or so, but I got right over to a diesel pump to fill it up. I know running diesels dry is bad, but I don't know the details.
I know I tried to put fuel in the front tank once and it was full. I'll double check that in the next day or so, now that you mention it...just in case I've missed something.
Thanks.
All at once, it hit me that maybe I was actually draining the rear tank. I threw the switch to the rear, and the guage dropped near zero. I didn't totally panic because I know the rear sender gives readings all over the place once I drive on the rear tank for more than 5 gallons or so, but I got right over to a diesel pump to fill it up. I know running diesels dry is bad, but I don't know the details.
I know I tried to put fuel in the front tank once and it was full. I'll double check that in the next day or so, now that you mention it...just in case I've missed something.
Thanks.
Logistics Pro
Joined: Apr 2004
Posts: 4,292
Likes: 5
From: NJ where fun comes to die
I had a similar problem with my 90. It turned out to be a bad power wire. Mine used to be a short bus, so it was hard to find out where the wire came from. Eventually I just ran a new wire from the fuse panel and cut the old one.
Also if you change the valve underneath, mine has two different size lines for supply and return. So you have to buy two size clips to replace the original.
Also if you change the valve underneath, mine has two different size lines for supply and return. So you have to buy two size clips to replace the original.
Last edited by trike1946; Jun 26, 2006 at 06:37 PM.
New User
Joined: Jun 2006
Posts: 7
Likes: 0
>>It turned out to be a bad power wire
Interesting...I wonder if old wiring is giving me low voltage at the solenoid. Enough voltage to make a noise, but not enough to actually flip the valve.
Does anyone know the how these valves work? Is the rear tank the position when no power is applied? Can they get stuck on either tank? I'm assuming it's a solenoid; is it something else?
I'll try pulling the wiring connector off (it' on pretty tight), and running a strong 12V to it. If I can drive around with it like that and the front tank starts emptying, then problem solved (I hope!).
Interesting...I wonder if old wiring is giving me low voltage at the solenoid. Enough voltage to make a noise, but not enough to actually flip the valve.
Does anyone know the how these valves work? Is the rear tank the position when no power is applied? Can they get stuck on either tank? I'm assuming it's a solenoid; is it something else?
I'll try pulling the wiring connector off (it' on pretty tight), and running a strong 12V to it. If I can drive around with it like that and the front tank starts emptying, then problem solved (I hope!).
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
Try disconnecting the fuel lines at the tank........ stops syphoning effect.
Anyone needing a new FSV for older trucks you can wrecker dive for an 88-97 diesel valve and ensure you get the newer connector since re wiring your old one would be required.
Anyone needing a new FSV for older trucks you can wrecker dive for an 88-97 diesel valve and ensure you get the newer connector since re wiring your old one would be required.
New User
Joined: Mar 2008
Posts: 7
Likes: 0
Hi there I have an 87 F250 6.9 supercab the valve is missing and the wiring is a mess I have just won a wiring and vac pipe diagram set on ebay as replaceing the valve & getting it all working is on my list so if your stuck for diagrams please get back to me it should be here in about 10 days to come, thanks for the tip on the water trap from Dave I wondered what that ring pull was for !, Jon.
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