S52 Misfire and possible fueling issue

[Poeman446]

I finished my s52 OBDII swap a few months ago, and it runs pretty well with the exception of a misfire every now and then. I couldnt figure it out for a while but I believe it is due to a pressure differential between my tank and the atmosphere. When I opened my tank to get gas the other day, I heard a sucking noise when I took off the cap, and pressed down on the flap in the fueling port. I believe that it's a vacuum in the tank, and not a positive pressure. Has anyone had this issue before, and what could be the cause?

I think that my evap purge valve is bad, but I believe my lines are hooked up correctly. I am using the OBDII running losses valve from a 99 M3, so that also may be an issue. All vacuum lines are either hooked up or plugged. The charcoal canister was deleted, and my evap line runs directly from the tank to the evap purge valve to the intake. I know this isn't correct, but I don't believe that would cause my problem. Any insight? I can reinstall the charcoal canister if need be, i was just trying to get some working clearance around my intake and other components.

If I ever do have a misfire in the car, I get out, equalize the pressure in the tank and restart the car. The misfire has always gone away after that.

Thanks!

[DesertBMW]

try running the car without the fuel cap, just put a rag, see if you get misfire, if you don't then fuel tank vending system is bad. It could be because of no charcoal canister

[328ijunkie]

Youre drawing raw vac on the tank. You need a charcoal canister or vent the tank to atmosphere.