Carb tuning w/O2 sensor

[Tom Kirkham]

Originally Posted by mrmustang

Tom,
...the placement of the O2 sensor plays a critical role in how accurate your readings will be. Mismeasurements by as little as one half and inch in either direction can mess up your readings by as much as +/- 10-15%.
Bill S.

Please explain. I have never heard of the placement being so critical.

NGK says

http://www.ngksparkplugs.com/pdf/AFX...ual_REV_06.pdf

"The AFR sensor should be located between 12” and 48” from the engine, upstream of any catalyst device if so equipped. The closer the sensor is to the engine, the more likely it will be overheated, possibly shortening its life. The further it is from the engine, the more likely condensed water will get into the sensor and thermally shock it, again possibly shortening its life. The sensor should be mounted at least ten exhaust diameters upstream of the exhaust exit (ex. for a 3” exhaust pipe, that is 30”). If the sensor is mounted between one and ten exhaust diameters from the exhaust exit, the AFR measured will be leaner than the actual AFR by as much as 2 AFR at low engine speeds (i.e. less than 3000 rpm)."