Fuel injection questions

[Phil Payne <quk@sievers.com>]

My careful rationalisation of the MB's method of operation is lying in ashes 
this morning, so I'm appealing for ideas.
 
Brief recap - the MB engine's "warm-up regulator" is exactly that.  There is no 
vacuum connection for fuel enrichment.  Question one - is this device (a warm-
up regulator with no provision for vacuum control) unique to the MB?
 
The MB also doesn't have a system pressure regulator inside the metering head.  
Instead, it has a "pressure regulator" valve mounted on a bracket behind 
the fuel metering head. I suspected mine was getting old (138k) and so decided 
to change it.  In the absence of a new part (eight weeks lead time from the 
Fatherland) I fitted one from a 60k car.  Then I conducted some experiments:
 
a) I used the on-board diagnostics to run the fuel pump and warm-up valve.  
Then I applied vacuum to the pressure regulator.  The fuel pump noise 
rose in pitch, quite noticably.
 
b) I got the engine idling to check the system and control pressures.  The warm-
up regulator does its job properly - starting at 2.something bar and drifting 
to 3.something bar over two minutes or so.  But the final control pressure is 
now 3.6 bar - it was 3.4 bar before I changed the pressure regulator.  So I 
believe my first hypothesis stands - in a steady-state warm MB engine it's the 
"pressure regulator" that is in charge of control pressure and not the 
warm-up regulator.
 
The surprise came when I applied vacuum to the pressure regulator.  As I 
expected, 0.5 bar of vacuum reduced control pressure - though by only 0.2 bar, 
much less than I expected. Question two - in cars with vacuum enrichment via 
the warm-up regulator, how much does control pressure drop for 0.5 bar of 
vacuum input?
 
A bigger surprise came when I measured system pressure.  I had hypothesised 
that the two were brought under one valve's control on the MB to allow system 
pressure to be increased as control pressure is decreased as a result of the 
vacuum input.  WRONG!  System pressure drops almost 1.0 bar with 0.5 bar of 
vacuum input.

Question three: is this correct?  I can't see how it can be.  I have a brand 
new pressure regulator on order from Bosch (six weeks to go - $160) and I have 
a workshop session booked with Martin at BR Motorsport a week on Wednesday.

Question four (addendum to Question one): do any other cars (not necessarily 
Audis) use a valve like this in a K-type Bosch injection system?

Bye-the-bye: I wanted to set the idle "properly" - 430ma through the ISV at 
800rpm and 0.75% CO - so I went out and bought a "Digital Automotive Analyser" 
made by Draper.  200mV to 600V DC, 10A, 200ohm to 20Mohm, diode, and dwell & 
tach for 3 to 8 cylinder engines - GBP26 ($40).  It comes with crocodile and 
probe leads, and is encased in a heavy rubbery housing, eminently suitable for 
concrete workshop floors.  How they do it for the money ... 

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