77 c10 dual tank setup, driver side builds too much tank pressure

[77c102door]

hey guys im having this continue issue with my fuel system. my setup is a 77 c10 that came with dual tank setup, however i have a fitech efi system with a fuel command center. i deleted the charcoal canister and the command center vent is vented to the hardline vent on my truck. I have my gas cap changed to a vented gas cap. Keep in mind the driver side tank never worked ever since i bought the truck. whenever i switch to driver side tank the gas gauge reads passed full, so it has to be a ground issue or the sender. i disconnected the vent line from the driver side and capped it, however i still have the outlet hooked up to the selector valve. The damn thing is still building too much pressure which causing the fuel to gush out from the gas cap. any suggestions?

 

[1987 GMC Jimmy]

All I know about this system is that the FCC vent is supposed to be routed directly to the hard line that goes to the tank, which you did. Is the vented cap part of it, though? If the FCC is supposed to exist in place of the charcoal canister, I would imagine you’d keep the smog gas cap so vapors would flow like they were intended to. Unless you’re following explicit manufacturer instructions, I’d see what they have to say about the cap. Otherwise, I’d check the line for restrictions. Blowing into it is a bad idea because there’s likely a little cage on the inside of the sender where the metal vapor neck goes into it, and that could collect the obstruction. If you can safely suck on it without huffing vapors, you could at least see if it was clear. I’m not sure what the best way to accomplish that is, but some sort of vacuum or siphoning device might be a good place to start. I’ve sucked on gas lines before, but I’m not that good at it, I have gotten fuel in my mouth, and I don’t want to suggest it to others.