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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 3,357
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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