The condition you described is indicative of a malfunctioning purge
valve on the charcoal canister and/or the BVSV valve is
closed/plugged. (BPSV is a coolant temperature controlled path for
canister vapors to enter the intake manifold.) If you remove the
fuel cap to vent all pressure, replace the cap for a few minutes, and
then find more pressure upon cap re-removal then you have fuel that
is being heated excessively. Ported vacuum is supposed to prevent
pressure build up in the fuel tank while driving ... but only if the
canister valves and BPSV valve are not clogged or otherwise
inoperative. A little puff of pressure is one thing ... a BIG WHOOSH
is quite different.
I had my garage check these today & they found both working fine. They put
the BVSV valve in a freezer then took it out & found it was opening &
Just now I tried removing the gas cap - and there is no Whoosh - and the car
keeps on running!! So maybe there was some kind of temporary heat-related
problem that caused the gas smell and the whoosh/stall on Saturday - or -
maybe when the garage removed & checked the parts then put them back on that
this made a better connection & that fixed it.
I just got back from a 1 hour highway run - the gas tank is now on empty -
with the car running I removed the gas cap - no whoosh and no stall. So
maybe as you say the garage got rid of an obstruction in the charcoal
cannister because I had noticed in the past what seemed like a vacuum when I
would remove the gas cap after coming off the highway with the tank on empty
(sort of the reverse of what I experienced on Sat with gas tank pressure).
Now if I could only get my intermittent starter problem fixed....
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