so i worked on a 99 k1500 today that had a p0446 code. heres how i diagnosed it:
- need to use a scantool capable of watching fuel tank pressure AND be able to munipulate the EVAP system (command purge on etc)
- i commanded the purge valve on 100% with the vent valve open. this is alowing then engine to apply vaccume to the evap canister and related hoses as well as the fuel tank. and yes you do wnat the vent valve open during this.
- while doing that above step i watched fuel tank pressure. went down to about -7.5 H20 and stayed there. acceptable vaccume though the system is -5H20 or less.
- i unplugged the vent valve from the canister (removing some restriction to the system) and now im looking at -6H2o
- still not happy with the resuls i unplugged the canister from the fuel tank and watched fuel tank pressure. took about 15secounds to to 0H2o. pressure should have equalized MUCH quicker then that.
- next step to try and find out where the restiction was was to take the other end of the hose (that goes from the fuel tank to charcoal canister) off of the fuel tank. (this is after i hooked everything back up to put vaccume back in the fuel tank)
- once unhooked from the tank pressure still dropped slow. so now i know there is a restriction in the fuel tank and the tnak has to come out.
this isnt the best detailed instructions but im just trying to give you guys some insight. pretty much theres a blockage in the evap system and the goal is to elimate peice by peice untill i find where the blockage is located.