Hey all -- I've been working on converting my 88 Trooper to diesel using the 4JB1-T engine and am currently modifying the fuel system.

I am removing the electric fuel pump and installing a pickup tube I made using some 5/16" fuel line, replacing all the rubber fuel hose with viton tubing (so no biodiesel rot trouble) and welding up the old holes for the pump wiring. Obviously, I am planning on using the stock tank. I am also replacing the filler neck with one from an 86 diesel.

I noticed the diesel filler neck has an extra port on it compared to the gas version. There is one small port and one large port on the diesel neck (one is about 1/2" dia and also present on the gas filler neck, the other is about 5/16" or a bit smaller in dia. and unique to the diesel filler).

Is it a vent? I am not sure how the diesel system is designed. There is no vapor recovery, but is there a vent to atmosphere? Is this filler port the vent? I was thinking I could hook it up to the vapor recovery ports on my gasoline tank if this were the case, would that be advisable?

Any help appreciated.