KISS System

Howard Wilkinson owly at mcn.net
Tue Feb 24 02:08:59 GMT 1998


There seems to be some objection to CIS type systems..... From what
I've seen they work well, and are simple.  Perhaps the best thing is
to have the injectors at the upper end of the intake runners in this
sort of system rather than at the port.
    It would seem to me that if you have a accurate measure of air
flow it should be unnecessary to have an O2 sensor in a feedback loop
once a lookup table is perfected.  An O2 sensor attached to a guage
would be useful in modifying the program though.  The mechanical
system I was describing which I have in a box has no feedback or other
systems to modify the mixture from what the airflow driven servo
determines.  The only electrical part on it other than the fuel pump
is a primer.   I always assumed that the overshot due to inertia of
the servo plate was what provided momentary enrichment on
acceleration.
    I suspect that once a proper lookup table was developed so that
the correct mixture was provided at all airflows the system would
function without the added complexity of a feedback loop.  Feedback
from the airflow sensor and the O2 sensor could be temporarily saved
to your laptop to help in modifying the lookup table as needed.  If
the airflow signal were modified mechanically by applying greater or
lesser resistance to the motion of the sensor choking for cold engine
operation could be accomplished without having to deviate from a
simple table.  One apparent airflow condition results in one fuel
flow.
    Using throttle position, and rpm and temp sensors you have a
situation where you have to determine airflow from throttle position
and rpm, then modify that value depending on engine temp to generate a
value from which to control fuel flow.  You then have an O2 sensor
that says "you're too rich" in response to which you have to change
the value, or modify the O2 reading or block it if you are in a choke
(cold engine) situation.  Or does the system operate on a 4
dimensional spreadsheet type of table with each piece of information
pointing to one coordinate of the table?
    It all seems a bit complicated to me, but I suppose the really
serious developers feed all the data into a computer which generates
and modifys the program as it goes along until you have something that
works and can be placed on your embeded controller.        H.W.





More information about the Diy_efi mailing list