Civic Si Lambda Correction
The Civic Si stock oxygen sensor is of a wideband type, however it does not read accurately once the mixture is richer than lambda 0.88 (13:1). Dyno testing shows that the stock oxygen sensor reads over 1 AF point different with rich mixtures.
A dyno run showing the difference between the stock o2 sensor and a wideband
However, our testing has showed that the difference between the stock oxygen sensor and the actual lambda is constant - there is no effect from exhaust gas temperature or time.
Effect of time and temperature on oxygen sensor and wideband readings on supercharged K20 at full load
On the dyno we measured the difference between the stock o2 sensor and the actual lambda.
Stock o2 sensor vs actual lambda
From there measurements we created a corrected AF sensor, using the correction as below. Mixtures leaner than lambda 0.95 (14:1 AF) were not corrected, even though the stock o2 reads richer than actual, in order not to alter the closed loop operation.
Lambda correction table
The corrected lambda sensor is available for datalogging and graphing as 'AF.Corr'.
Stock o2 lambda reading and corrected lambda
The corrected lambda reads very close to an aftermarket wideband.
Dyno run showing stock o2 reading, corrected lambda and actual lambda.
Disclaimer: We made every effort to accurately record the differences between the stock o2 sensor and actual lambda - on the test vehicle the stock o2 was replaced, the exhaust system was checked for leaks, a brand new, freshly calibrated wideband lambda was used with the o2 sensor being placed next to the stock o2 sensor. Testing was conducted on a load dyno with long settling times to obtain an accurate reading. However, it is possible to your results may vary from ours. We recommend the use of a dyno when tuning, especially for forced induction. In any case the corrected AF as reported in our software will always be leaner than that reported by the stock o2 sensor, so you will be safer using the corrected AF than relying on the stock readings.