1991 E150 5.8 Liter Midship Gas Leak

[ChadH]

I have a 1991 E150 with the 5.8 Lite with duel gas tanks. I had a mechanic replace the rear tank that was leaking when I engaged the fuel pump (turned the key). In hind site I'm not sure the tank needed replaced but it was along with the fuel strainer. The mechanic didn't think the tank was used for a while; it was full of a bunch of black gunk at the bottom. Rear tank doesn't leak anymore. The gauge says it's empty and it sounds kind of hollow when I tap on it but I can't get much gas in it from the station.

The mechanic said the way Ford designed this was with 3 fuel pumps, one in each tank and a third outside that automatically flips from one tank to the other once you run one tank dry.

Recently I would smell gas from in the cab when it's hot out but not all of the time. I also noticed fuel leaking from the midship tank now. I ordered a new fuel pump with the o ring thinking the smell and leak was likely coming from that. However, after dropping the tank, the pump and o ring looked fine but the rubber gromet housing what I think is the vent valve at the top of the tank was rotting pretty bad. I found a new rubber gromet at Ace Hardware for $1.65. Put everything back together, new pump, o ring and gromet and the 16 gallon tank took about 18 gallons at the station and puked probably close to a gallon on the pavement. I drove home on the midship tank and no leak. Since the rear tank gauge doesn't work, I like to drive on that tank first for a while and then flip to the front tank. When I drive on the aft tank, the midship one leaks, like a strong leak. Any idea what would be causing this?