aliens8mycow

I didn't see this exact issue covered yet, so here we go. I have a 91 f150 with the 5.0L engine and dual tanks.

I recently replaced the rear tank, pump, sending unit, wiring harness, and filter. Obviously, that works pretty good now!

Here's the deal - the front tank doesn't work. Never has since I got the truck. There's a fuse for the fuel tank in the panel under the dash, but it's missing the connector on one side - would/could that be the reason why the front tank doesn't work? I guess the real question is, is there a way to wire in an inline fuse and bypass the one in the fuse panel? From there, I could see what other issues I might be facing, such as a bad switch, bad fuel pump, etc.

Second question - remember, rear tank works, front doesn't - the front tank is full of gas (empty when I bought the truck, and has never been filled from the spout)!?!?!?! What the hell is up with that? This one doesn't have the 3rd fuel pump on the frame rail - could the valve where the two lines connect be worn out and back-flowing into the front tank? It's full to the point where there is pressure built up - If I take the cap off, fuel will spill out. I'm hoping it won't build pressure past the normal system pressure and blow up the tank or anything... Until I get the front tank running, could this cause problems? I gues the good news is that the front sending unit works - it shows full if I switch to that tank. (maybe that rules out the switch being bad too?

There's no real hurry on this, since the rear tank works (as long as the front one isn't going to blow up!)

Just call me Sean

iTrader: (1)

Your front fuel pump is bad. When you switch to the front tank and the gauge works that is showing that the switch works. The valve that prevents fuel from being pumped to the wrong tank is part of the fuel pump. Each pump has one. The front tank pump valve isn't working allowing fuel into that tank. It's going to continue pumping fuel into the front tank until it spills out. It's only the return, so the pressure may not be enough to spill the tank over, but the tanks have a vent that may allow fuel to come out anyway. The valve may have recently messed up and that's why no fuel has spilled out yet. The fuel pumps don't run off a fuse anymore, but they used to and the fuse box lettering wasn't changed through this model run, that's why it isn't used. The pumps run off a fusible link.

aliens8mycow

Well, that was easy...

I assumed it was the pump, since it's the biggest hassle to replace. (that's just my luck)

Thanks for the reasonable explanation - I guess I'm gonna spend a few hundred more $$$ soon. Since the gas that's pouring out of the front tank is full of flakes and smells like it's got water in it, I'll probably do the same as the rear tank and replace the whole thing while it's apart.

Just call me Sean

iTrader: (1)

Nevermind, I thought I was wrong, but I was incorrect.

Just call me Sean

iTrader: (1)

Same as above, wrong, not wrong. Not about your problem, just other info I had.

aliens8mycow

Ok... let's see here. I have a working tank in the rear, and the front one needs a pump (maybe the tank too). It's building up enough pressure to leak out the filler cap on the front tank.

At this point, I'm not ready (ok, my wallet is not ready) to replace the whole front tank/pump/etc.

This leads me to a few questions:

Is there a way to bypass the connection between the two tanks and bypass the front one altogether?

Can this be done without messing things up for when I decide to get the front one back in order?

Should I just open the front tank every day or two to release pressure and keep things simple?

Thanks for any advice you can offer!

Just call me Sean

iTrader: (1)

Because your truck is newer than mine it doesn't have a switch so I'm not sure where the line tees off at, but it does tee off somewhere. If you can find the tee and get it apart without any drama you can remove the front tank line and splice the rear together only without a tee. Unfortunately I doubt you will be able to do that so the only other recommendation I have for you is to unhook the return line at the tank and put a cap on it to stop fuel from coming out of it. I think you only need to do the return line. Get it apart and see what size fuel hose will fit over the end and then find something to cap off the hose. You need to use fuel hose for fuel injected vehicles and fuel line clamps also for fuel injected vehicles. There is a difference.

aliens8mycow

Thanks - I'll give it a look, and hopefully find some way to do this without causing problems/cost for later. If it looks like I'm going to create a mess and cuss myself when I'm ready to get the front tank working again, I think I'll just have to go ahead and replace the fuel pump.

It's killing me as it is, because it builds up enough pressure in the front tank to make it seep out around the filler cap, and at almost $4 a gallon, that's gotta stop.

aliens8mycow

I found the split in the return line - it's just a plastic Y fitting. Do you think I can cap the fitting end that runs toward the front tank and be good, or should I run some hose and clamp it like you mentioned before? It looks like a real joy to get to, since it's in the frame rail along with all the other send/return lines for both tanks (and not much room to get at it with the tank a few inches away).

I'm really not sure if I have the guts to start messing with the fuel lines... I don't want to cause more problems for later.

Just call me Sean

iTrader: (1)

I don't know what the y looks like, but it's probably not made to be taken apart. Another option is to take a pair of vice grips and pinch off the line, but you can't pinch it at any plastic section of the line, you have to find a rubber spot and I'm not sure if there is even a rubber spot.