We installed and tested a M&W UEGO linear O2 sensor in both the DP and the end of the cat back exhaust. We did not observe any noticeable differences in the AFR readings.

Someone had asked me this question and I just got around to testing it.

Being futher away from the turbo and with cooler temperatures, the self heating sensor will last longer.

 

Hi Chuck, so I can have an o2 bung welded just in front of my cat on the pipe for tuning purposes? I don't want to mess up the ceramic coating on my dp, and do not want to go thru the hassle of swapping the cat out for a mp for tuning.

 

Only if it is a self heated O2 sensor!

 

I think a little farther away from the extreme heat and pressure might help it last longer/more reliable. Half way down the DP or something is where I am going to mount mine.

Tim

 

I've had some problems with bad readings after cats. It might work sometimes but other times it hasn't. I would recommend not using a wideband that way unless you are just trying to see if the a:f is in the ballpark (e.g., wideband reads 11:1, a:f might actually be 10:1 or 12:1). Normally the reading will be leaner than actual so it is a valid way to see if you are RICH enough, but don't try to do precision tuning this way.

I would recommend using the sensor at the end of the downpipe or just before the cat. Running a sensor at the stock location will damage some wideband sensors.

I still use a tailpipe probe for my own car and other cars with no cats.

Wade

 

When tuning with my horriba widebands, I found that
any measurement down from the stock O2 sensor location would give approx 1/2 AFR richer reading. This
is also the case with piston cars especially like
single turbo supras. And yes this is very hard on sensors
but considering the cost of single turbo, highboost cars
its worth it.