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Old 11-15-2012, 10:42 AM   #26
Scooby Specialist
Member#: 268354
Join Date: Dec 2010
Chapter/Region: NESIC
Location: Massachusetts
02 WRX 05 LGT
Slow Automatics


Originally Posted by the suicidal eggroll View Post
Probably for rapid closed loop changes. The farther the sensor is from the heads, the more delay you get between combustion and measurement. This will effect the behavior of the closed loop system, enough delay and you can start to get oscillation. This has nothing to do with whether or not the measurements are correct though, just the time delay in getting them.
I'd buy that as the major reason to why the sensor is in the uppipe. I've also been under the impression with low exhaust gas flow, its readings are more stable being closer to the ports. The other thing is it probably gets up to temperature quicker there, and has less of a chance for water vapor to collect in it.
Originally Posted by NSFW View Post
For the twin-scroll cars, Subaru actually did put the front O2 in the downpipe.
Hmm, interesting.. Probably so they could get readings of both banks with one sensor. No doubt the OEM unit is a wideband, and could be used as one (besides the rich limit), I'm just saying if it were optimal to have it the downpipe (in context of stock ecu/ CL parameters, etc), all turbo models would. As far as simply monitoring AFR for your own use, putting the O2 in the downpipe is the way to go.
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Old 11-20-2012, 11:24 PM   #27
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Member#: 258723
Join Date: Sep 2010

I'm pretty sure you're farther away mounting is fine ... as I've seen pretty consistent readings vs various in car widebands in different cars against the dyno's wideband they stick in the tailpipe.

There may be slight variance, but I'm going to go out on a limb and say your placement is just fine. It seems per the instructions (and the UEGO instructions I have sitting on my desk for my newest build) the real danger is too close to the exhaust ports (high egt's getting the sensor too hot) and leaded fuels cuttings it's life by 2/3's if not more.
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Old 11-21-2012, 01:09 AM   #28
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Join Date: Nov 2012


I was going through some old logs and found that my WB reading was spot-on (i.e. same as final fueling base and OL map all the way through to 7K rpm) until a certain day, and after that day it started reading leaner.

I installed an electronic boost controller (HKS EVC) that day.

I'm running only a couple of psi above stock with EVC and I wouldn't have thought that would throw the WB reading off.
Had a look under the hood but I couldn't find any sign of leak after MAF that would make the WB read leaner.

So I don't know. I adjusted the MAF scaling anyway to compensate for it..
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