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WinRice WinRice is offline
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Join Date: Jun 2005
Location: Colorado
Posts: 700
Originally Posted by 911st View Post
The pressure above the plunger would however increase to equal system pressure and system pressure it's self will not be effected in any manner.

The fuel that was going to be passed through the WUR would just pass out the FD's system pressure regulator and go back to the fuel tank.

Blocking the Lambda Frequency Valve however would effect AFR's as it would reduce the pressure differential. Doing this will not effect System Pressure ether. Just lower chamber / differential pressure.

Thus, there is no reason to maintain any special level of Control Pressure unless it is going to be used as a spring / force to keep the control plunger from advancing unnecessarily and or it is to high, as if blocked, it might take somthing like 25 lbs of force to push the control pin up against it. (Anyone know the surfice area of the control plunger.)

A simple over the counter pressure reg (as suggested) in the place of the WUR that is calabrated would work just as well and alow such a system to be offered in a standardized kit form. Or just leave the WUR in place and work with it.

Again, good stuff.
I pretty much agree, I was going off you first comment that blocking off the WUR would effect the lower chamber pressure, and from my highly tuned memory () of the system. Now I'm looking at the Bosch manual.

The lower chamber sees the regulated system pressure, then the upper part of the plunger sees pressure from the 'decoupling restriction' which then leads to the WUR.

So if you blocked off the WUR, the plunger would see the full system pressure. If your stepper or servo could handle the force, it wouldn't be an issue. That could be a sizable force. Looking at the 928 rebuild guide, my highly calibrated eye () estimates the plunger diameter to be around 3/4" dia, so at 100 PSI that would be 44 pounds of force. No wonder the flap needs a good mechanical advantage through the lever. So you would want to bleed this off as much as possible to make the plunger easier to move.

I guess the proper way to block this off, would be to seal off the 'decoupling restriction' and the return line from the WUR to the system regulator, then you shouldn't have any CP?

Or just tie the WUR lines together and return all the fuel from the top of the plunger.
1986 911 Turbo
3.3L, K27HFS, Tial 46mm, TurboKraft Intercooler, 964 Cams, Monty Muffler, MS3Pro Evo, M&W Ignition, Zietronix WBO2 Data Logger, Wevo shifter, coupler and motor mounts.
Old 09-24-2010, 02:50 PM
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