Q about placement of wideband A/F sensor

[richardholdener]

The position of the oxygen sensor in the exhaust system will not change the reading (rich or lean). The farther away from the cylinder head, the air/fuel curve will have basically a time lag when compred to engine speed. This means that the curve will be the same with respect to rich or lean, it will be just shifted slightly in the rpm range. Once agin, no change in air/fuel reading from change in position of oxygen sensor or from having catalytic converter in system (seems odd but back to back tests reveal identical air/fuel before and after cat).

Originally Posted by LtNoogie

I just wanted to get this straight in my head. The further back one places the wideband A/F sensor, in the exhaust system, the leaner it will show? i.e. most accurate is in the header, more lean after first cat, more lean after second cat.

The reason I ask is that when I dyno'd the car, the mechanic read the A/F mixture from the tailpipe. The entire A/F curve is probably shifted slightly to the lean side, right?

TIA

[largeorangefont]

Originally Posted by richardholdener

The position of the oxygen sensor in the exhaust system will not change the reading (rich or lean). The farther away from the cylinder head, the air/fuel curve will have basically a time lag when compred to engine speed. This means that the curve will be the same with respect to rich or lean, it will be just shifted slightly in the rpm range. Once agin, no change in air/fuel reading from change in position of oxygen sensor or from having catalytic converter in system (seems odd but back to back tests reveal identical air/fuel before and after cat).

I agree. I have seen slight variances at idle when taking AFR readings pre and post cat, but these seem to go away once the car is moving.

I've actually tested with 2 widebands at the same time.

Are you going to run a wideband in the car or do you just want a bung for testing?

[The Spectacle]

Originally Posted by richardholdener

The position of the oxygen sensor in the exhaust system will not change the reading (rich or lean). The farther away from the cylinder head, the air/fuel curve will have basically a time lag when compred to engine speed. This means that the curve will be the same with respect to rich or lean, it will be just shifted slightly in the rpm range. Once agin, no change in air/fuel reading from change in position of oxygen sensor or from having catalytic converter in system (seems odd but back to back tests reveal identical air/fuel before and after cat).

I know this is old but I stumbled across this post in a google search and I feel obligated to post...this is plain false. The futher away from the motor (or conversely the closer to atmosphere you place) the o2 is the leaner it will show relative to another o2 placed further upstream in the exhaust system. Tailpipe sniffers on dyno's have free air going past them and will read leaner.

[127.0.0.1]

Originally Posted by richardholdener

The position of the oxygen sensor in the exhaust system will not change the reading (rich or lean). The farther away from the cylinder head, the air/fuel curve will have basically a time lag when compred to engine speed. This means that the curve will be the same with respect to rich or lean, it will be just shifted slightly in the rpm range. Once agin, no change in air/fuel reading from change in position of oxygen sensor or from having catalytic converter in system (seems odd but back to back tests reveal identical air/fuel before and after cat).

never put an engine controlling air/fuel sensor behind a cat. you do not want the computer running the engine based on reading from behind a cat.