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Location: Glorious Pac NW
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CIS control pressure management

OK, I've read enough positive reports about folks managing control pressures with the Andial frequency valve - and smurfbus's recent report about managing the CP via lambda control valve - to be convinced I want to try this. Rather than dump on the existing threads, I thought it would be better to ask my dumb questions on a separate thread

My '78 930/60 has (as far as I can tell) a non-lambda RoW fuel head. So I can't easily do what other folks are doing.

However, I can't see any good reason why it wouldn't be possible to get the same effect by modulating (via a frequency valve) the pressure line from the top of the fuel head to the WUR and bleeding off excess pressure to the return side. Am I missing something? This is how the WUR regulates the control pressure, right?

Is there some magic in the circuit in the lambda fuel heads? Seems to me that the WUR regulates the control pressures via that line - so why wouldn't that work just as well as the lambda valve and/or the Andial frequency valve?

Also, peering at Theirry's thread, I notice from this picture

that the Andial valve will bypass the pressure input to the WUR directly to the return circuit on the fuel head.

If I'm seeing this correctly, this approach requires two non-standard hollow bolts to take two fittings (one on the top of the WUR, one on the fuel head return fitting).

Why? Anyone have any thoughts as to why this was done this way?

Wouldn't bridging the standard WUR fuel feed/return lines with 'T' pieces on the middle of the hose run and a frequency valve joining the 'T' pieces have precisely the same effect to override the WUR? The WUR can't keep the pressure high if the frequency valve is in the same circuit and bleeding it off, right?

Input and sanity check welcome!

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'77 S with '78 930 power and a few other things.

Last edited by spuggy; 11-07-2010 at 03:04 PM.. Reason: Fixed URL to image
Old 11-07-2010, 03:03 PM
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The stock lambda frequency valve on a stock unmodified aluminum USA lambda fuel head doesn't have any effect on control pressure like it appears your thinking.
It has no relation to control pressure at all.

The lambda frequency valve modulates lower chamber differential pressure in the fuel head to lower emissions and get better gas mileage when cruising and idleing. It does that by returning fuel to the return line going back to the gas tank.

This system along with a catalytic converter is what allowed Porsche to meet the EPA emission requirements to resume selling the 930 in the USA in 1986.

hope that helps.
Old 11-07-2010, 04:11 PM
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Quote:
Originally Posted by JFairman View Post
The stock lambda frequency valve on a stock unmodified aluminum USA lambda fuel head doesn't have any effect on control pressure like it appears your thinking.
It has no relation to control pressure at all.

The lambda frequency valve modulates lower chamber differential pressure in the fuel head to lower emissions and get better gas mileage when cruising and idleing. It does that by returning fuel to the return line going back to the gas tank.
Yes, the lambda frequency valve controls the lower chamber differential pressure, rather than the control pressure fed into the WUR.

But the Bosch K-Jet documentation states that the individual differential pressure valves on each fuel delivery outlet maintain the upper chamber pressures to within .1 bar of the lower chamber - so wouldn't it be true that modifying the lower chamber pressure directly modifies the upper chamber pressure as well?

As smurfbus is controlling the lambda valve with an AIC/1 and affecting his WOT AFR's, it would appear so...
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'77 S with '78 930 power and a few other things.

Last edited by spuggy; 11-07-2010 at 05:48 PM.. Reason: fix quoting
Old 11-07-2010, 05:33 PM
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Spuggy, you editted your post while I was writing a reply to the post you had befroe you changed it so now i have to change mine to keep from looking like an idiot...

OK, you got it right now but what you have written above after editting is now completely different from what you wrote before, and what my reply was referring too.

so it goes...


Last edited by JFairman; 11-07-2010 at 06:42 PM..
Old 11-07-2010, 05:52 PM
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