MB engine CIS system

[quk@sievers.com (Phil Payne)]

Any of the experts care for a quick speculate?
 
I'm trying to establish a theory of operation for the fuel injection system on 
the ur-quattro MB engine.  I'm especially interested in WOT fuel enrichment.
 
The system is standard CIS K-Jetronic - up to a point.  There is no vacuum 
connection to the control pressure regulator (a.k.a. warm-up regulator), and no 
pressure control valve in the metering head itself.
 
Compared with the WR system, there are two notable additions.  One is what the 
German documentation calls a "membrane valve" - it's connected to air mass 
sensor upper chamber and is the jumping off point for the fuel return line.  
The other is what appears to be an electrically controlled valve.  The membrane 
valve is clearly shown in the microfiche drawing, although there is no 
discussion of its function or of testing it.  It holds vacuum.  The other valve 
_is_ mentioned in the microfiche (as "valve N") and the on-board diagnostic 
trick for actuating it is discussed. There's no discussion of what it _does_ or 
any way to measure its effect - you apparently stick a stethoscope on to see if 
it's clicking!
 
>From the wiring diagram, valve N is a "Taktventil fuer Lambdaregelung" - a 
frequency valve for lambda control.  Odd - because there is no lambda sensor 
anywhere on the car, and no catalyser.  It runs on leaded petrol.
 
Anyone care to speculate on why things are as they are?

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club