Mixture question

[brett at netacc.net (Brett Van Sprewenburg)]

On May 23, 2006, at 11:05 AM, Drew Mac wrote:

> On 5/23/06, Dan Bubb <jdbubb@verizon.net> wrote:
>>
>> It's long been my understanding that adjusting the mixture on CIS
>> mostly affects idle and has less and less of an effect as the fuel
>> metering plate moves higher.
>
>

Yes, this is the case (idle mixture affected more so then high rpm
running).  Here's an excerpt from an email I wrote back in December
of 2000:

 From the Bosch Fuel Injection 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."


Remember this is a mechanical bias adjustment that changes the  
relationship
of the air flow plate to the fuel metering plunger for the entire  
operating range of
the mechanical plate.  For a given volume of air moving through the  
air box,
the plate will "float" to the same height.  Alter the relative  
relationship to
the fuel metering plunger via mechanical means and you've got a  
change in fuel
delivery for a given volume of air at every value of the air flow plate.

So, yes, it alters the AFR throughout the operating range of the air  
flow metering
plate and therefore engine operation.

==Brett