CIS Control Pressure Question -- Adjustable WUR Question
 

Why does lowering the control pressure in a CIS fuel system enrich the air/fuel mixture? Intuitively, it seems that if you lower the control pressure then you allow more fuel to flow back to the fuel tank thereby diverting fuel away from combustion.

With respect to making the WUR on a CIS system adjustable, does the "aftermarket" plug adjustment set-up described in detail in many posts on this list allow you to adjust cold control pressure or warm control pressure or both? If I understand correctly, adjusting the plug adjusts the position of the bimetallic strip and the bimetallic strip overrides the spring pressure. Once the strip "heats up", it lifts up off of the plate and allows the internal springs to take over the upper diaphragm pressure. So the strip affects cold control pressure only. If this is correct, how do I adjust ward control pressure via the WUR?

Thanks,
Duane Duclaux
Richmond, VA

For your first question:
The WUR applied pressure to the top of the control plunger. So, if there is more pressure on the top of the plunger, then it cannot move as far in response to engine vacum. Therefore, less fuel pressure is directed to the injectors. If the WUR allows LESS pressure to the top of the control plunger, then it can move more in response to engine vacum.

The 'plug' adjustment changes your warm pressure. I think you need to shim it internally to change the cold pressure, IIRC.

I'm going to recant he statement above:

http://forums.pelicanparts.com/porsche-911-technical-forum/165146-wur-vacuum-question.html?highlight=WUR