[Diy_efi] Effect of detonation on measured mixture?

Bruce nacelp at bright.net
Fri Apr 26 18:42:52 GMT 2002


The O2 sensor is a reflection of what's going on in the chamber.
It ASSUMES, that things are OK.   Now the trick word is *things*.  Meaning
mechanical errors, and chemical properties can affect what it *thinks* it's
seeing.

If you are to believe the SAAB patents (amongst others), then there is an
ionization level change that accurs at or near detonation.   If some
remnents are left and in the exhuast stream, then they have to have some
effect on the chemical reaction in the sensor.

I wouldn't put total trust into any readings taken when things are WRONG.
ie in detonation.  But, I don't put total trust into anything other then
reading the plugs.   Seeing any signs of detonation on the plugs puts the
whole tune into guestion anyway.

Remember the DIY is not a lab grade devise nor was it ever represented as
one.

You have to test for timing as a function of performance, so in your travels
you will see the indicated AFR change as you move the timing around, so you
do have to chase back and forth in getting a calibration right.

If your running with the timing too far retarded and the reaction is going
poorly in the chamber then advancing the timing will change the indicated
AFR in the direction of leaner (in my experience so far).  I added 4d (may
have been 6) timing at idle with no other changes and the AFR went from an
indicated 13:1 to 14.5:1.

All tuning means finding what the engine wants and giving it that.
Bruce



----- Original Message -----
From: "Shawn Fogg" <sfogg at attglobal.net>
To: <Diy_efi at diy-efi.org>
Sent: Thursday, April 25, 2002 7:49 PM
Subject: [Diy_efi] Effect of detonation on measured mixture?


> How, if at all, does detonation effect the mixture seen by an O2 sensor?
>
> I was adjusting the mixture on my supercharged Z3 trying to eliminate a
little bit of ignition retard I was seeing WOT due to the knock sensors
kicking in.
>
> I enrichened the mixture (+4%) in the area of the knock (around 4300 and
up) and retested ignition and mixture. Now I wasn't getting the ignition
retard but my mixture actually looked leaner in that area.
>
> I'm assuming this is because I'm getting better combustion in that area
(no detonation so a few more degrees of advance) but wanted to confirm that.



_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi



More information about the Diy_efi mailing list