[urq] Into the CIS abyss

DGraber460 at aol.com DGraber460 at aol.com
Sun Nov 21 22:51:51 EST 2004

In a message dated 11/18/2004 5:17:10 PM Mountain Standard Time,  
martin at quattro.ca writes:

...  getting back to the CIS tuning ... I think the first thing I  would
recommend is to read through the widely available Bosch documentation  on
the CIS system to gain a full understanding of how it works.   For
example, you could have done the same thing as cranking all ports  45
degrees by reducing the control pressure.  In fact, assuming that  your
OXS feedback is working you should expect the duty cycle on the OXS  Freq
Valve to compensate for the richer mixture.  It seems to me  the
adjustments for the individual ports might help with balancing  the
cylinders ... such as richening or leaning particular cylinders based  on
the inspection of the spark plugs after a run  ...

Well received and done. I had read before but a review was in order.
I do disagree that the same result would come from reducing the control  
pressure. I know and agree that such will richen the mixture. I have played with  
that over the years and it never yielded any WOT positive improvement.
I have felt (thought) that "richening the mixture" via control  pressure 
concerned idle and partial throttle- not WOT. I believe (and could  be full of 
crap) that WOT calls for max system flow at factory setting which is  limited to 
a preset max flow spec. I ventured down this path hoping to  flow more fuel at 
WOT, while still utilizing all the system controls at idle and  partial 
throttle. It appears to have done just that, although I will need to  verify with a 
fuel mixture gauge in the future (like when I can again become  gainfully 
After reviewing the CIS documents, and totally dissassembling a spare FD to  
examine its innards, my instinct tells me that turning the screws out  
(counterclockwise) should lean the mixture, as it reduces the spring pressure on  the 
diaphragm in the FD. This is confusing, but imperical evidence is conclusive  
that WOT is noticeably improved! A quick plug read, shows good cylinder 
mixture  conditions, and the FV is still hanging around 40-45 as before. 
I would caution anyone else to not mess with this setting unless you have a  
spare stock FD to return to. I am out on a unverified, unscientific limb of  
experimentation, and at 5k' elevation. Your experiance may seriously vary!
Any feedback appreciated.
For the past few days I just can't wait to drive the car.  Transformed  from 
"fun" to "great fun"!

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