'86 F-250, 6.9L diesel, dual fuel tanks ...

This air intrusion stuff is driving me nuts. I get the truck running great for a few days, then let it sit and it won't start again. Not running at the moment.

But after crawling under the truck and discovering all the crazy stuff previous owner(s) did to the fuel lines and selector valve(s), I'm thinking I'm just going to replace lines. Not terribly expensive and should help with air leakage issues.

Problem is, I can't figure out how the selector valves are supposed to work. I seem to have two of them, daisy-chained together. The lines coming from the engine are plastic, one grey and one blue. The frontmost selector valve has both these lines connected to it, but three out of the four lines that are coming off the back of that valve have been tied off. Only one line comes off the back of it, then connects to a second valve. There is an electrical connection, with 5-6 wires, to both of these valves.

In short, I have no idea what's going on here. It would seem to me that each tank should have a source (drain) and return line, and the selector valve should have two coming from the engine and four going out to the two fuel tanks. It would appear, though, that my return line does not actually return to either of the tanks.

Would anyone be so kind as to provide a diagram or description of how all this is supposed to work, so I can make some sense of it? I've got a good handle on how everything from the water separator onward ties together, but fuel selectors aren't making much sense. Thanks.

 

After thinking it through, what appears to be the case is that someone who owned this truck before I did replaced the stock fuel selector valve, but did two things I don't understand: did not remove the original fuel selector valve, and did not replace it with a six-port valve.

I've got two still hooked up: the stock valve and the replacement. But since the replacement valve is only a three-port, the PO plugged three of the ports on the original valve and hooked a fuel line between it and the new valve. Then connected the two tanks to the replacement valve. Both of the valves are hooked up electrically, so I guess they're both operating when I hit the switch.

So although my return line is still connected to the original valve, the return line on the other side of the valve is plugged. In other words, my return line goes nowhere.

From what I've read, this isn't exactly good for the long-term health of my injector pump.

So I guess it's time to yank both these valves and replace with a known working six-port valve. Anybody got a recommendation? Rock Auto has four of them, but I can't tell a difference other than $40-$50 between the most expensive one and the least expensive.

 

Not starting may be due to fuel draining off the IP and filter...... this can be caused by air intrusion to any part of the fuel system......usually in the return lines, filter or fuel connections on the engine..........

Granted the BS around the selector valves does not sound good, PO may have had a third tank in the box????

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