I'm lucky enough to own 2 F-150's. One is a 94 4x2 - 5speed and the other is an 88 4x4 - auto. Both are 4.9L 6 cyl's. longbeds, pretty standard trucks...

I run both trucks until the gas tank is coughing and sputtering, then switch to the other tank.

When the 94 runs out, and I hit the switch, it takes a second, maybe two, until the engine "catches" again and runs fine. The 88, however, takes 30 or so seconds for the stalling/sputtering/bouncing to stop.

My question is this - Why the time difference? Am I missing something with the 88?

It's usually running out at 25MPH - so I have to find a place to pull over.

Any thoughts would be appreciated

 

Quit running it out of fuel. That is the worst thing you can do. The pumps have screens on them so when you run them empty, they are sucking all of the crud from the tank. This cannot be good for the fuel filter either. I imagine the screens on the '88 are slightly plugged or the filter is plugged.

I have the 19 gal tank on the front and the 18 in the rear. Since I get 10 MPG in the city (all the driving I do is back and forth to work- about 10 miles each way in the city) I have a paper where I write down my miles plus 180 when I fill up. When I hit that mark, I switch to the rear tank. I have yet to sputter. Just my $0.02

 

Thanks! I purposely empty the tanks. I did that when I first got the trucks, and as soon as the second tank emptied, I replaced the filters. I fully expected the sludge and crud to come though, and it did. I can and will continue to run the tanks dry. It's the prudent thing to do, especially when one is trying to clean the tanks out from the mess that's in there.

But that still doesn't help the problem with the time problem with the fuel system. Unless you are thinking that the reason that there is a hesitation is that the four fuel filters that I've put on the truck in the past four months aren't doing their job and filtering the fuel.

I know the junk that can come through - which is why I let the tanks run dry. That is what the filter is for. I can't be the only one with twin tanks that drys them out regularly...

 

The 88 has three pumps, two in-tank pumps and a high pressure in-line pump on the frame rail. Some fuel is kept in the dual function reservoir (which is the switching valve) to keep the high pressure pump fed, should the in-tank pumps momentarily fail to pickup fuel. I'm guessing that the 30 seconds is how long it takes for the in-tank pump to replenish the fuel in the reservoir.

As for running the tanks out of fuel: the pumps are cooled and lubricated by the fuel flowing through them, so running them dry can overheat the pumps and reduce their life. As long as it is just something temporary to clean the tanks, you should be okay, but I wouldn't run every tank dry.

 

Ummm...tanks always draw the fuel from the bottom, so the pump will pick up any sludge, goo, gunk, flakes, etc. no matter the level in the tank.

As for the fuel cooling/lubricating the pump, that may be true to a degree, but the amount of fuel going through these pumps at any given time is so small that the cooling is insignificant. I've always run my tanks dry before switching, and have yet to replace a fuel pump.

Otherwise, what Eric said is true that the '94 has a high-pressure pump in each tank. The '88 will only have the high-pressure pump if it is EFI. If it is carbed, it may have a mechanical "suck"-type fuel pump on the engine, hence the long wait for the engine to catch back up. (My friend had an '88 E-150 with a carbed I6 in it, and it was the same way when you ran a tank dry--took forever to catch up again unless you were above 25-30 MPH).

Jason

 

Fuel flow through the pumps is what 80-something LPH or something like that? That doesn't sound very insignificant. The fuel actually passes through the electric motor itself, cooling the motor. There's no airflow through the windings like a traditional electric motor, so something has to take the heat, and that ends up being the fuel on its way to the engine. Try running the pump dry on a work bench continuously without fuel and see how long it lasts.

 

The transfer unit (reservoir, etc) is also different for those years you have. I had to replace the one on my 88. One point on the cooling effect of the fuel: It's not only the fuel going through the pump which cools it, but the fuel in which the pump is submerged. It's your truck(s) do as you like, but I try to switch mine at 3-4 gallons remaining.

 

What cools the in-line pump on the frame...it isn't surrounded by fuel, and it's surrounded by a thick piece of foam and a steel sleeve, so it isn't air cooled either. The surface area (heat transfer area) of the fuel touching the inside of the motor is much, much greater than the surface/heat transfer area of the exterior of the pumps.

 

Thanks for the input, guys - I didn't think about the fuel being the coolant for these things.

When I bought my 1st F-150, I switched the tanks often, but I was always worried about "what if" I had to go longer, so I ran it dry - then did the same thing to the other tank. Since then, I've changed the filter at least 4 times, worrying about the deposits from the bottom of the tank.

I pretty much know how much fuel they have, and when I'll run out. Now that I've been edumicated ( ) I'll switch before the tank goes dry.

Thanks again!!!