farmerjg

2001 WS6

My check engine light is showing P0440. I've gone 70 miles on this tank and my fuel gauge is reading half full....or half empty. The tank immediately prior to this one got ~150 miles on half a tank of interstate driving (I was running rich from a bad O2 sensor, that's been fixed). The car lives in a garage and the garage does not smell of gasoline before or after driving. Thoughts? Can my gas cap be so loose when the system pressurizes I'm actually evaporating off gas? While I haven't done a smoke test, the purge valve and connecting hoses appear to be in decent condition (meaning no cracks). Help?

angel71rs

Loose gas cap will set code cause it makes it impossible to build & hold vacuum level needed to pass test cycle. But don't think a loose cap will cause your fuel mileage to tank.

Only thought... when charcoal cannisters go bad, they can allow bits of charcoal to get sucked up to purge valve. If that prevents it from closing, will constantly apply vacuum to tank, perhaps sucking gas vapors into your engine... and your fuel mileage with it.

To check, remove purge valve, tap it to see if charcoal crud falls out; if it does, your evap cannister is falling apart. I found it easier to pop off front hose where it hooks to intake manifold... couldn't unhook the damn thing from the purge valve while installed.

farmerjg

Not that I really expected anything different (because nothing is ever what it's supposed to be), but I pulled off the purge valve and there was no crud anywhere. The parts didn't even appear to have dirty interior walls. I suppose I need to change the gas cap then do a control test on the highway to find out my true mileage and to see whether or not I'm really losing gas or if my right foot is causing the poor mileage. 6th gear going 70 down the interstate should get me high 20 mpg's, right?