I ave a 92 chevy silverado 350 i removed the canister purge valve a while back ago and caped the line giong to the fuel tank and every time i take the gas cap off it has alot of pressure is this bad for the engine or what can it do? Do i need to vent the gas tank ? And if so why?

 

the tank should vent through the evap charcoal canister. if pressure gets too high the cap is designed to release this pressure. Working properly, all the venting should be through the canister. the purge side should not effect this. check to see if the vent line from the tank to the cannister is clear. if ok, check that the canister is not clogged.