What Happened To My Hissss? P0446?

[helomechs]

this started about 9 months after i bought the truck, (bought in jul 03) its an 03 silverado extended cab 4.8L

 

i got a p0446 evap sys malf. i also noticed my hisssing sound when i open the fuel tank had dissappeared. i know the system vacuums out air during cold start ups 15-85% fuel level etc. and that was probably my hiss right? regardless i ignored the code cause i dont have to smog it anytime soon. well i erased it and it didnt come back for a year. erased it again maybe anothe 6 mo. before it came back. so i did lots of research on this site and concluded i should replaced the purge solenoid and upgrade to the "robust vent valve" since these were the 2 most likely causes judging by several topics on this site. i erased the code and it has yet to come back. but i really expected to hear that hissing noise again and since i dont i am expecting to get that light back again. will somebody clue me in on whats happening? how do i know replacing those two components did anything?? and should i be concerned that my tank no longer hisses? be advised i currently have a loss of injector pressure problem which i am sure is a back check valve on the pump assy.

 

this new robust valve.

 

i read that you need the vent valve (32$) which is about 2.5" round instead of rectangle like the stock one. so i was told i also needed a bracket (57$) THIS WAS NOT NECESSARY. NOT ONLY DID THE NEW BRACKET NOT FIT IN MY TRUCK I JUST BENT THE STOCK ONE A FEW TIMES AND IT WORKS JUST FINE. SO THAT MAY SAVE OTHER LIKE ME A FEW BUCKS. the purge sol. cost me 20$

 

the vent valve is on top of the "charcol" canister in front of my tank. very very difficult to replace with tank installed but possible