[alfa] Re: alfa-digest V9 #1175

[alfa@xxxxxxxxx]

> Date: Fri, 12 Mar 2004 17:29:47 +0000
> From: webb.p@domain.elided
> Subject: Re: [alfa] Re: alfa-digest V9 #1174
> 
> The O2 sensor should be as close to the exhaust port as possible.   The
> 'correct' (should be indicated) AFR is constant throughout the exhaust prior
> to the CAT.  What's usually at issue is the EGT.  Non-heated sensors need to
> be much closer to the port to maintain heat to report correctly.   If you're
> running lean and your EGT goes above 1500degF, you could damage the sensor.

This is 1/2 the story...  Temperature is a major issue to get the sensor working
properly, but just as important is the ability to see all the cylinders to get
a proper chemical signal to the catalyst.

My suggestion would be to find a generic 3 wire sensor and run it at 12V all the
time.  Or perhaps have a WOT switch to turn it off at wide open throttle- don't
exactly need it then.



> 
> If you felt extremely frisky, you could go WB02.   The WB02 controllers from
> Tech Edge run about $100-200 and the LSU 6066 Bosch sensor is about $50
> nowadays from Volkswagen.   The WB02 sensor puts out 0-5v true AFR.  The
> controller outputs 0-1v to input to your ECU.  WB02 records true, realtime
> AFR not a slow reacting guestimate the NB02 does.   The controllers usually
> have either lights or displays to indicate AFR which makes tuning your
> modifications much much easier.
> 

That is an expensive solution to a simple problem, my friend.


> Disconnecting the O2 sensor forces the ECU into open-loop mode with no
> feedback.   NB02 sensors are usually VERY slow and mostly inaccurate.   The
> usual failure mode of a bad NB02 sensor is slow response to the feedback loop
> in the ECU, making the car run badly.
> 
Peter, peter, peter... do we have to go over this again???  NB O2 sensors are
generaly FASTER than WB ones, more importantly, the switch point for a NB
sensor is far more consistent than a WB one.  That, I do know from real
experience- seeing it right now for control purposes, and NOT for some
aftermarket gizmo.  For the current breed of sensors, they are fast enough to
see a voltage shift if one cylinder is lean of stoich while the reast are rich.
 It's a real annoying problem to have to fix, but it happens.

Find a good 3 wire sensor, add the O2 boss after all the cylinders run together,
which should be just before the catalyst.  You will be all set.

Eric Storhok
Ann Arbor, MI
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