At 10:40 AM 6/15/2001, Russ Gunter wrote:
>  The gas pump will not operate if there is a significant leak in the
> system because it needs a vacuum to pull against.

Eh?  I think you need to re-examine this statement.  The Bosch pump is a
roller pump; analogous to a gear or flexible-impeller pump in its operating
principle, i.e. it is a positive-displacement pump that takes fuel into a
rotating chamber, then reduces the volume of the chamber which causes the
fuel to squirt out under pressure.  It will create a suction on the input
line to pull fuel in if gravity flow isn't sufficient, but it doesn't
depend on that suction for operation.  Of course if it's easier to pull air
into the pump than fuel, it will pump air, though not as well as gasoline.

Like most (all?) in-line FI fuel pumps, it is cooled and lubricated by the
gasoline passing through the motor on its way to the actual pump.  That
means the pump spends some power trying to spin the armature through all
that nasty thick gasoline, but I guess it solves enough other problems
(notably shaft sealing) to be worth it.  But it means that the lifetime of
a pump running dry is probably measured in single minutes.

>  So, I am going to replace the gas tank (it is badly corroded) and work
> at replacing all the rubber and plastic gas lines.

A worthy enterprise, I'm not trying to discourage that!  Though the plastic
line is probably all right, they seem to be very tough.

david

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"