Fuel Pressure and the filler neck...

Hi all.. quick question..

My service engine light is on pertaining to fuel pressure. Removing the gas cap and greasing the seal will keep the light off but after a few days it comes back on (particularly when the tank gets below half). Today I noticed that the little metal flap on the filler neck is stuck open. My question is does this little flap contribute to sealing the opening and hence fuel pressure? If so then this is most likely my next plan of attack.. picking up a new cap tonight to see if that makes any difference.

Thanks!

What do you mean by "pertaining to fuel pressure"?What you descibe is the EVAP system,I do believe.A new cap might fix the problem.I'm not sure about the flapper.When I put a new fuel pump in,I had the light on and it turned out to be that the o-ring on the pump assembly didn't seal right.I have read on here that traceing down a problem in the EVAP system can be pure hell,but the problem is usually the gas cap.