O2 sensor location

[Terry Martin]

Michael J Weber wrote:
> 
> At 12:35 PM 9/9/97 -0700, you wrote:
> >On Tue, 9 Sep 1997, Todd King wrote:
> >
> >>      <<<
> >>      On a home-built Turbo/EFI performance system using an aftermarket ECU,
> >>      should the O2 sensor be located before the turbo or after ? If after

> >>      Do like the oem's do- put it before the turbo. The stock loc on mine
> >>      is about 2" before the turbo.
> >>
> >>      Todd       todd_king at ccm2.jf.intel.com
> >>
> >Haven't really thought to look at several turbo cars for this feature,
> >but Mitsu eclipses and Audi turbos have them after the turbo, so perhaps
> >there is no universal law for placement...
> >
> >Seth Allen
> >
> All the Grand Nationals and Turbo Regals have the sensor in the downpipe
> after the turbo.
> 
> Mike Weber
> mweber at interaccess.com

It depends on the ECM/PCM/OBC/ECU/VCM-A calibration, (whichever you
prefer, computer geeks like alphabet soup), among other things.

Pre-turbo results in a different O2 reading than after turbo, simply
because the turbo a) adds more time in the exhaust stream, and extracts
energy, and, b) because of the delayed sensor reading, post turbo
results in a cooled, energy deficient, oxygen used, exhaust stream being
measured.  

If nothing else, O2 measurements are temperature dependant because of
the partial pressures of the various gasses.

Terry