OK, I asked this question a few years ago and really could not get an answer.

Question: what does a catalytic converter do to a wideband sniffer's accuracy out the tailpipe during dyno?


Here is my scenario: Went to my shop and did a pull. Before I started the run, the AFR on the monitor was showing I was above 16:1 at idle. My car was running perfect so no way was I off that much.

OK, so I start my WOT. The car starts lean and slowly moves towards what I had tuned in as an AFR.

Is it correct to theorize that the cat will affect AFR? Is it also correct to assume that as I push more exhaust through it at WOT that the cat cannot burn off that extra fuel fast enough thus why I start the pull lean but ending close to where I want in AFR?

Another thing to consider is does a wideband read AFR or does it read CO and HC levels? I understand CO and HC levels change through the cat but the AFR does not.

Ben

 

Sure... the cat uses the O2 in the exhaust to combine with unburned HC and CO. The wideband can only "see" O2.

You don't put the wideband after the cat(s). You unscrew the stock pre-cat O2 sensor and screw the wide band into the bung.