MB fuel system

[Phil Payne <quk@sievers.com>]

In message <970420110121_-2104205379@emout08.mail.aol.com> Raudi83TQ@aol.com writes:

> 1. Your control pressure regulator (aka WUR) has no vacuum lines, so it has
> no ability to respond to boost?

Correct.  Which is why (despite Charles Probst's recommendations in his 
otherwise excellent book) I've gone back to calling it a "warm-up regulator".  
For the MB, that's the only function it performs.

> 2. Your lambda valve has no O2 sensor so it is not for emissions control.
> What does feed it with power to regulate duty cycle? (I assume the ECU, so
> I'm looking for what sensor input here. I am guessing vacuum/boost.)

Yes, it's the ECU.  But what inputs the ECU uses ...  I don't know.  I had 
assumed the WOT switch and perhaps boost - it also looks at various temperature 
sensors, I gather.  I'd like to find a spare MAC-12 and get one of the experts 
to disassemble the code ...

> What I found was that the addition of vacuum control to the control pressure
> regulator was to improve emission control, then later to allow response to
> boost on turbo cars. Older K-basic systems had no vacuum lines, so it mainly
> responded to block temperature and electrical input, hence WUR.

WR engines in the UK all have vacuum to the warm-up regulator (in this context, 
Probst is right and it should be called the "control pressure regulator).

> The lambda valve was added to further improve emissions control. This use 
> on your MB is unique in that it has no emission control function, but is 
> being used to regulate fuel delivery in response to some other input.

That's how I see it.  

> I am guessing that the control all lies with the fuel distributor piston with 
> input from the other two.

I'm beginning to suspect that the warm-up regulator has no function at all once
the engine is warm.  Both the control and system pressure lines are taken to 
the "pressure regulator".  Twiddling with its vacuum affects both.

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