1991 International Transit Bus 3400 T444E 7.3L turbodiesel.
Been trying to diagnose an air in the fuel problem, traced it back, fixed a few things, now everything runs fine …if you bypass the fuel tank and pull from an external can of fuel, but not from the stock tank. Installed a lift pump right after the tank, but when hooked up to the stock tank it just pulls in air. Put in one of those little clear mini fuel filters (hate the threaded opaque mini filters they give you with those little green aftermarket electric diesel pumps). The clear mini filter just shows the residual fuel left in it and a lot of bubbles when the pump is on. Probably not a vacuum from a venting problem, otherwise there would just be no movement, no bubbles, I figure. Pump is really close to the tank and low down an claims to be self-priming, so I doubt it’s having trouble priming (and pulling from the portable tank sitting on the ground and thus lower was still no problem with this pump). Even tried a hand bulb primer pump in line with it, still air from the stock tank (though this hand primer is kinda cruddy, always breaks and I have to patch it up, hard to find a place that sells them around here).
I’m going to double check and redo all these tests I guess… But in the meantime, what could possibly go wrong in the tank?? What’s in there? (Or not in there, that should be?
The stock tank is huge and mounted under behind the big doors between the exhaust and side panels with not much space around it in an otherwise spacious undercarriage. It’s got the fuel out and fuel return connections at the center of the top of the tank, there’s barely enough room to get my hand up in there, much less a wrench, so there’s no way to undo the connections or remove the assembly without cutting a huge hole in the floor of the bus (if there even is a fuel assembly, it looks like it might just be two right angle connections for each just going straight into the sheet metal of the tank, but I can’t tell because there’s 20 years of this weird black coal-dust stuff piled on top and caked on.) Looks like there might also be a pair of wires, pretty sure thats the sender unit for the fuel gauge, I don’t get the impression this had a lift pump inside the tank.
Since the connections are on the top, wondering if there’s some sort of pipe going down inside to the bottom where I would assume fuel is picked up. Does anyone know if this is the case on this model? If so, do those things ever rot off or come loose? And, again, if so, what to do about it? (Besides the obvious of cut a hole in the floor, or sever everything and drop the tank). If not, well, I’m stumped as what else could possibly cause this.
If it is that, maybe just siphon the tank, drill a hole in the bottom of the tank, and thread in some cheap connector, basically make a new fuel out port?