[Walt Fricke]

Listen to Steve

The stock sensors and system produce a curve which basically has three slopes when it has voltage on the vertical axis, and AFR (or Lambda) on the other. It starts out a nice shallow angle, with modest changes in AFR for voltage changes. And at the other end, it is also at a nice shallow angle. However, in the area of interest between say 12 and 15 or so, it is very steep - there is just a very small voltage change between 12 and 15. So you don't really know what is going on, other than are you pretty lean or are you pretty rich.

At least for the CIS system using Lambda (maybe the 3.2s also?), this didn't matter to Porsche. If the sensor reads lean, the computer adds more fuel. On the 3.0s this is via the frequency valve in the WUR circuit. When it reads rich as a result, it feeds less fuel. The result is a kind of dynamic average for best part throttle fuel economy. This back and forth is by design. Works just fine to produce the fuel efficiency Porsche wanted. But not for tuning race motors, or home brew EFI systems.

As a result, we fool ourselves if we think we can use a stock sensor and a voltmeter (or an array of colored LEDs) for tuning of any sensitivity, if at all.