[urq] Into the CIS abyss

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Mon Nov 22 14:16:08 EST 2004

... no big deal on my part, but I thought I'd point out that the person
who made the comments on the CIS that you quoted was me, not Martin ...
wouldn't want anyone accusing Martin of saying something he didn't say!

I still believe that you should be able to do the same thing as tweaking
the regulating valves to each injector equally by adjusting the control
pressure ... the only thing the metering head knows about WOT is the
position of the metering rod, which is based on the amount of air
flowing into the engine.  I suppose one thing that could happen is that
the rod could top out and saturate ... if that was indeed happening then
the solution you propose would be a possible work around.  Lower control
pressure means that the metering rod will move more for a given amount
of airflow, so it might be more likely to cause the rod to run to the
end of travel.  Has anyone confirmed whether or not this happens, say on
a car that is running higher than stock boost?  

My concern is that the CIS system is based on regulated pressures, and
it is my understanding that the adjustments on the metering head that
you are adjusting are intended to set the pressure to match the pressure
that the injectors open at.  The other variable is the OXS Freq Valve
contribution ... this may be varied based on WOT as the ECU is in
control of the duty cycle ... 

I've wanted to instrument the engine up a bit more to test some of this
stuff myself ... my plan is to actually install gauges for the control
pressure and duty cycle so that I can see them from the cockpit while
the engine is running.  I've even thought about installing EGT sensors
for each cylinder in the exhaust manifold.  

As they say, nothing succeeds like success ... and it sounds as though
your test worked for you ... that's cool!  It will be interesting to
hear what you find in terms of idle and partial load performance ... 

Steve B
San Jose, CA (USA)
> 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 employed).
> 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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