quattro digest, Vol 1 #582 msg #14

[isham-research.freeserve.co.uk at pop.pol.net.uk]

> Sorry, De Witt, your theory about the lower o-ring and the purpose of
> the air shrouding is frightenly wrong. The injectors are "air shrouded"
> as a means of cooling them. No air is introduced into the fuel and
> atomization remains unaffected ...

You're the one frighteningly wrong.

There is an air gap between the tip of the injector and the little
brass cap on the end.  Air is forced down between the cap and the
body of the injector - its sole purpose is to improve fuel
atomisation.

Obviously pushing the cap too far onto the injector would defeat this,
so the tip of the injector itself has three small dimples spaced
equally around it to show how far the cap should be pushed on.  It's
quite common for the cap to be left behind in the seat when the
injector is pulled out.

Note, incidentally, that the hose connecting the inlet manifold and
the head to supply these shrouds is not a hose, it's a part.  There
is a constrictor inside it and it should never be replaced with just a
length of hose.  It's possible for high boost levels to pop injectors
out otherwise.

The factory microfiche also says that no meaningful tests can be
performed on an injector that has been out of the car for more than
an hour.  I suspect this is because an internal seal dries out, and
I always keep this type of injector in a small jar of fuel if it's
out of the car.

--
 Phil Payne
 UK Audi quattro Owners Club
 http://www.isham-research.freeserve.co.uk/quattro
 Phone +44 7785 302803   Fax: +44 7785 309674