re: How do I adjust Air/Fuel mixture?

[imlomax@xxxxxxxxxxxxx]

Scott Goodwin <scotti@domain.elided>
Subject: How do I adjust Air/Fuel mixture?

>>>>>>>>>>>>>>>>>>>
Ok, now that I've replaced my O2 sensor (with a generic Bosch single
wire unit), and installed a fancy air/fuel mixture gauge, I can see that

my newly-built 3.0 power plant is running rich (especially above 3000
rpm's at sustained speeds).
So how do I lean it out?  I'm aware of a hex screw on the Bosch Airflow
meter, but which way do you turn it?  I've experimented with it some,
but can't seem to find a pattern.
By the way, I have a modified black box, airflow meter... which may
account for the rich mixture?
Anyone know where I can find some information about tuning a Bosch
Airflow meter and/or setting the CO on an L-jetronic system?
>>>>>>>>>>>>>>>>>>>>>>>>
Scott,

The problem with using an o2 sensor for a measuring instrument is that
you only know that it's rich or lean, not <how> rich or lean it is.  I
thought the black box was supposed to richen the mixture at higher
RPM's, so it sounds like it's doing it's job.  If you don't see black
smoke while you're accelerating, you're probably ok.

There is a book on maintaining and tuning Bosch Fuel injected vehicles,
and I think it's available from IAP and others.  I forget the name off
the top of my head, but that would be a good place to start.  There is
not a whole lot you can do with a Bosch injected car.  They run pretty
good right out of the box, and are hard to improve on.  Just running
richer is not going to get you any more power, a common misconception.
Does the black box also raise the rev-limiter?  That I see as a useful
addition.  Running richer at higher RPM's is often done just to cool the
combustion chamber, then extra fuel does not add extra power.

Good luck!

Ian Lomax
Former powertrain engineer
Pittsburgh, PA

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