What are differences in WB AFR readings from before cat, after cat and at tail pipe?

[Chalky]

Has anyone had a chance to compare afr readings a on the same tune but sampling WB AFR at different points in exhaust system?

I know there is not absolute answer but there must be some consensus on what impact taking readings before, after cats and using a tail pipe sniffer will have on wb afr readings.

I am sure the best readings are at collectors and before the cats but in the real world, most people do not have bungs before the cats and most tuners are tuning using tail pipe sniffers.

[chpspecial]

Has anyone had a chance to compare afr readings a on the same tune but sampling WB AFR at different points in exhaust system?

I know there is not absolute answer but there must be some consensus on what impact taking readings before, after cats and using a tail pipe sniffer will have on wb afr readings.

I am sure the best readings are at collectors and before the cats but in the real world, most people do not have bungs before the cats and most tuners are tuning using tail pipe sniffers.

On my 2004 silverado SS with an STS kit, the readings where less than .01 AFR. the pre cat WBO2 sensor was an innovate LC1, the tailpipe WBO2 sensor was the innovate LM1. this was with cats still on the truck.

[ScarabEpic22]

On my 2004 silverado SS with an STS kit, the readings where less than .01 AFR. the pre cat WBO2 sensor was an innovate LC1, the tailpipe WBO2 sensor was the innovate LM1. this was with cats still on the truck.

Really? Hmmm good information. Was this at WOT or cruise?

[chpspecial]

Really? Hmmm good information. Was this at WOT or cruise?

it was both, I wanted to verify the readings off the lc1 by intalling the lm1. I too was surprised to see the little varience. however, this would only apply to vehicles that do not have an airpump at the cats. luckly GM doesnt use air pumps on our trucks.

[Highlander]

I never noticed much if at all a difference, before or after the cats. IF you can put them before, then by all means do so... If you cannot put them before, doesn't matter. Point is. the shorter the distance the more accurate it will be to fix the MAF table.

[johnv]

I haven't seen alot of difference, you can see erratic readings at idle from the tailpipe if you don't have a good probe for the sensor.
And as said by Highlander the closer the sensor is to the engine the less lag you get and the more accurate the reading will be for the VE table cell that your logging.

[ScarabEpic22]

Hmm, well I stand corrected for preaching about only going pre-cat for WBO2s. I do like mine being nice and close though, throttle changes are very close to reported WB readings.