Tank Vapor Pressure

Peter Petersen pwpetersen at earthlink.net
Wed Jul 3 12:15:47 EDT 2002

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Hi Guys:

I'm going to try this one again because I don't think I described the
problem well enough last time and it's a pretty scary problem.

The problem I'm having is with excessive pressure in the gas tank.  On a
hot day, after I have been driving for a couple of hours, if I loosen
the gas cap, fumes rush out and continue to do so for several minutes.
It's almost as if the gasoline has been heated to an excessive temp and
the vapor pressure at this temperature is significant.  If I were to
remove the cap immediately, there would be a fume jet shooting out of
the tank in quite an explosive fashion.  One static spark and were
talking serious BBQ

Also, the pressure does not diminish rapidly, almost like vapor is being
replaced by additional fuel boil off.  Again, pretty scary.

I recently had the fuel pump replaced and the work is somewhat suspect.
I'll take a look at the plumbing tonight.  Is there any chance the
mechanic could of screwed something up with the plumbing and the fuel
pump is pressurizing the tank by air-rating the fuel?  (the car does run

Another possibility: the fuel pump is staying on after engine shut down.
The fuel, passing thru the rail is becoming a heat soak for the cooling
engine and higher temp in the tank = higher vapor pressure.  I'm
currently checking to see if this is happening, but I haven't caught it

Any other suggestions greatly appreciated.  I'd hate to end up in the
papers for starting the next Colorado wildfire with my Audi, or worse
yet, rolling in the bushes trying to put myself out...



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