GM '89 Bosch MAF - was RE: MAF & base fuel tables

[Mike Pitts]

The big question is, how do you know 850mv is really 13:1? 

Standard O2 sensors behave more like a digital switch than 
an analog feedback sensor.  If you ever look at the response 
curve, you will see it's *extremely* steep around approx 14.5:1 
to 14.9:1.  This is the desired behaviour of a standard O2 
since the ECM switches between lean and rich such that it 
averages out to approx 14.7:1.  Outside of that range, there is 
no guarantee any two O2 sensors will return the same voltage 
for a particular A/F ratio. 

Basically all you are guaranteed of at 850mv is that the mixture 
is richer than 14.7:1.   Could be 13:1 or 14:1 or 11:1. 

A UEGO is much different.  It has an oxygen pump that is driven 
by the ECM.  The reading portion of the sensor is the same as a 
standard O2 sensor in that is switches around 14:7:1.  The big 
difference is that the ECM can add O2 to the reference side of 
the sensor to move the switch point up and down.  The amount 
of current that the ECM has to supply to maintain the switch 
point determines the actual A/F ratio.  At least, that's the way I 
understand it to work.

-Mike

-----Original Message-----
>I don't understand the UEGO statment though, the standard o2 sensor woke
>very well for you application, generaly most of these engine reach amax HP
>arround 13:1 AFR or about 850 mvdc.