I have two questions -

1. Both my fuel gages on the dash do this same thing - when I fill the tanks the gage goes way past the full mark. After running almost all the fuel out the gage comes down to 1/8 tank mark. When it hits the empty mark it is empty. It seems to work fine once it comes down to the 1/8 mark. It will bounce back and forth between 1/8 and full right before it drops to the 1/8 mark and stays there. Any information on this problem?

2. My selector valve is sticking open to the back tank. I filled both tanks this weekend and ran it on the front tank. The truck shuts off pereotically and when I switch it to the back tank it starts running fine again. It ran on the back tank the whole time even though I had the switch on the dash to the front tank. I know this because when I went to fill up the tanks the front was still completly full. Can these selector valves be fixed or do I need a new one and if so where can I get one?

Thanks in advance for any help!

 

welcome to fte.

here is a tip: put what year truck and any other important info in post.

you should only have one fuel gauge.

on fuel crossover do an advanced search in this forum for more info.

i never had one go bad and i do not offhand remember what needs to be done to fix it.

 

Sorry, the truck is a 1988 F-150 4x4 with duel tanks and one fuel gage on the dash for both tanks. The gage acts the same no matter what tank is selected.

 

It sounds like the fuel pump in the front tank is not working properly. The fuel switching valve is pressure operated by the in-tank pumps, so without the front pump working, the high pressure pump will draw from the rear tank as long as it can maintain prime, even without the rear pump running. A new pump/sending unit should fix the gauge issue as well.

 

I have the same fuel gauge problem on my 87 F350. When full reads full but below about 1/2 tank the gauge bounces back and forther between full and empty until I run out. Anyone had a simalar problem? I am assuming it is the gauge cause both tanks so both senders do the exact same thing.

 

My truck recently started doing this, but only on the front tank. I replaced the rear sending unit soon after I bought the truck, and the gauge reads perfectly when running on the rear tank. With 183,000 miles and 21 years, I just figure the sender has some breaks in the windings.

 

Thanks. Sounds like I need to start with a new sending unit in the front tank. I will let everyone know if this solves the problem.

 

Update - I am not in a hurry with this so I am trying one thing at a time. Last night I replaced the switch on the dash for the tank selection. I figured that if the back tank works fine even when the switch is in the front setting that maybe the switch was bad and not switching the pumps in the tank. well it still does the same thing. So I wonder what will happen if I switch the lines at the manual selector valve on the rail? If the front tank then works (with the switch still on the rear tank) that will tell me that the selector valve is bad. If it doesn't work then that will tell me I need a new pump in the front tank. Does that sound like a plan? Will this work?

 

Sounds like a good idea, you'll be able to pin down the actual problem and not just throw parts at it.

 

My '88 has always acted about that way since I got it over 10 years ago. On mine the guage will stay on full then suddenly drop to about 1/8 full, at which time I switch tanks. When mine drops to 1/8 I think I actually have about !/3 tank left, I never figured it out exactly comparing how much gas it takes to refill with the claimed capacity in the owners manual. I don't consider it to be a big problem, because I always fill both tanks and reset the trip odometer. I do like to follow the 1/4 tank rule though. NEVER RUN THE TANK BELOW 1/4 FULL BECAUSE THE GAS COOLS THE FUEL PUMP. I know a lot of people think that rule is BS, but I have always followed it and never had a problem with a fuel injected fuel pump.

 

I don't like going dry by any means (usually 1/8th tank is my limit), but the fuel that flows through the pump is what cools it, not the fuel surrounding the outside of the pump. So theoretically, as long as there is fuel flowing through the pump it will stay cool.

 

I keep my tanks full for another reason. Ya just never know when something is going to happen that makes fuel unavailable.

 

Ok, so I unhooked the fuel lines (delivery and return) at the mecanical selector valve from the front tank. I had someone turn the switch to the run position and nothing came out of the lines with the selector switch on the front tank on the dash. When the switch was turned on I could here a pump start, I think it was the high pressure pump on the rail and only for a second or two. It is my understanding that I should have had gas flowing out of the delivery line and into my bucket at this point. Is this correct and if so I assume that I have a bad in tank pump in the front tank and this is what I should replace next.

 

how can you possibly keep them always full?

when you are on a trip do you stop every 10 minutes to fill up?

every day on the way home from work do you fill up?

every trip to the store do you fill up?

 

So am I on the right track? If I unhook the delivery and the return lines from the valve and turn on the ignition switch to run I should see gas coming out of the delivery line into my bucket from the tank? I realize that I would only have to unhook the delivery line.