Farm trucks, popular where I live, are good for hauling a horse trailer, a boat, a hay-bale fork, or spike trailer. After working with a beater S10, then a Silverado, then a Ford Explorer, I was ready for something that drank less and cooled the cabin more. It turned out the local service station had just the truck -- a compact SUV rescued from a write-off that could haul a ton and had functional air.
One of the chores a farm truck often endures is launching a boat or jet ski in the shallow waters of the local dual-use irrigation/boating lake. When the water gets low, the ramp goes to a shallow angle, so my beater soon found itself in water two inches below the sill while I launched a jet ski. After two outings of this kind, it gave up, two miles down the road from the launch.
The fuel tank had taken in a half-gallon of lake water. In the course of drying the system out, we noticed there was something strange about the fuel pump assembly. This import SUV’s fuel pump is a fuel-injected multi-port, like most these days, so the pump is relatively high pressure -- 40psi above manifold pressure, vacuum, in fact. The pump sends fuel to a fuel injector manifold, and a regulator sends the excess back to the tank.
This particular model formerly had an inlet sock filter on the fuel tank floor and a return pipe that fed back to the tank base. Someone evidently had an idea: "Let's put the fuel pump in a plastic can and feed the return fuel into the canister, too. Then the pump would more likely be covered -- with a cooling and quieting effect." That's the way I visualized things in the design group in South Korea, anyway.
It was a good idea, but there was a little problem: the can had to admit fuel from the tank, but it didn't get it via an external sock inlet. Instead, the sock was folded neatly inside the can, and to admit fuel there was a little orifice in the foot of the can with a wire strainer over it, so more fuel could get into the can.
Now it is true that if you want fuel to flow from a tank to a can, there has to be a little pressure differential -- lower on the inside. So the can would have to have a fuel level lower than the tank fuel level. Even worse, if the can's orifice became constricted, the level in the can would drop faster than the orifice could supply it. The result was that the engine would start, run for a mile or two, then stop until the fuel percolated into the pump canister.
If only the inlet fuel sock was piped outside the can. The can would then always be full with the return flow, which I imagine was the desired effect. It took $600 worth of mechanical investigations to get to this final stage, after the pump and filters had been changed.
This entry was submitted by Brian Whatcott and edited by Rob Spiegel.
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