Re: [Tech]: O2 sensors

[Brett Van Sprewenburg <brett@netacc.net>]

>>From: "Chris DeLong" <green536@hotmail.com>
>>
>>ok, if you disonnect the freaky valve and the lambda switch then 
>>you basically have a regular CIS system. Any adjustments made at 
>>idle will affect the entire rpm range. just cause you adjust it at 
>>idle doesnt mean it wont change the geometry inside the fuel 
>>dist/air box assy.
>
>That's what I thought too, at first. But That's not what my air fuel 
>gauge was telling me. Stoich at idle dropped off below the scale 
>when the motor was revved, even just a bit.


Lest I repeat myself, but from the exact same book chapter 5, section 2.1
"Mixture (CO)":

"To ensure that the basic air-fuel mixture is in the best range for emission
control, all continuous systems have a provision for mixture adjustment.
Although this adjustment is made at idle, it affects the basic sensor-plate
and control-plunger relationship over the entire range of operating conditions.
For a given lift of the sensor plate, the lift of the control plunger is
adjusted to change the amount of injected fuel, and therefore the air-fuel
mixture."

>
>I have 2 bits of evidence to back up what I previously stated ("You 
>need to get the whole distributor from a non-O2 equipped car")
>
>1. Simply disconnecting the frequency valve is the same to the fuel 
>distributor as having a frequency valve connected, but running at 0% 
>duty cycle. That will make it run lean
>
>2. The mixture adjustment screw is ONLY for idle mixture adjustment. 
>It does NOT have the same effect over the whole airflow range. 
>Here's a quote from Charles O. Probst (from his awesome book "How to 
>Understand, Service, and Modify Bosch FI and engine management" 
>Chapter 7, section 5.2, Part "Mixture Adjustments" Paragraph 3)
>
>"Competitors in the now defunct SCCA Rabbit/Bilstein Cup racing 
>series (for near-stock, Volkswagen Rabbit sedans equipped with 
>K-basic) used to carefully adjust the idle mixture to a very rich 
>setting-the rules prohibited any real modifications. The result was 
>that the large enrichment in fuel mixture at idle brought with it a 
>smaller but meaningful enrichment at high rpm, where it would give a 
>little more power."
>
>The key point here is that the _Large_ enrichment at idle does NOT 
>cause the same enrichment at high rpm.
>
>HTH
>
>Jonas

While I agree that changes in the mixture screw will affect idle more
so then high rpm running, which is blatantly obvious as the motor can only
burn so much fuel at idle, while the same motor can use up more fuel
at higher rpms; all relatively speaking of course.  Saying it doesn't affect
the entire operating range of the motor is not correct though.  Perhaps
we're actually in agreement here... :)

==Brett

 \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're small"
\/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | - brett@netacc.net

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