Re: Ur-quattro's Deceleration valve?

[DeWitt Harrison <de@aztek-eng.com>]

On Sun, 18 Oct 1998 00:32:07 -0400, Martin Pajak wrote:

>What does the deceleration valve do on the 1983 Canadian Ur-q do?
>I am trying to clean up some of the unnecessary vacuum lines and was
>wondering how important is it?  It sort of looks like a blow-by valve
>except it's hooked up to the intake rather than before the turbo.

The valve prevents the dumping of unburned hydrocarbons at
throttle closure. When you lift, the throttle shuts faster than the
fuel distributor can back off on fuel delivery resulting in a momentary
excess of fuel at the intake ports. The decel valve opens at that
moment allowing unmetered air to enter the system to combust the
extra petrol and, possibly, to allow the air metering arm to fall faster.

It is also yet another example of the band-aid, fix on top of fix
widgets the Bosch boys had to resort to in order to make the CIS
idea work more or less properly.  If you are worried about it,
there are plugs available from Audi to close the holes in the
air box and the intake duct after you rip the junk out. Look
closely at the microfiche. No change in starting or running
performance,. Just one less source of unmetered air and a lifetime
of guilt from emitting the occasional puff of unburned hydrocarbons.
I don't know if I can continue to live with myself.

DeWitt Harrison
Boulder, CO
88 5kcstq