Re: [alfa] Re: alfa-digest V9 #1175

[webb.p@xxxxxxxxxxx]

> > 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.

With a batch fired system, there's no perceptable difference in AFR from one bank to the other.   The only exception to that would be an injector or driver failure which would only take out 1 cylinder.    I'm limiting this statement to batch fired systems of Jetronic/Motronic-1.3 vintage.   Modern batch and sequential systems aren't that simple.

> 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.

L-Jet already goes open-loop at WOT.

> > 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.

Depends what problem you're trying to solve.  On a stock daily driver I'd tend to agree.   The poster indicated modifications to his car and looking for performance.   Every tuner I've read or talked to works with WB02 for performance engines, including every dyno shop in my area.

> 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.

Read the Tech Edge data sheets or better yet look at the MS target AFR code.   There's no way target AFR would work with a NB02.   It requires WB02 for it's speed and accuracy for sub-second correct based on Lambda feedback.   

O2 crossover tuning is an educated guess at best, and I've witnessed that trying to tune the Verde on a NB02.   Everyone in the MS community suggests tuning with WB02.   I can't wait to get my Precision Wideband Controller that B&G just released to get my tuning right once and for all.   

The 1000's of running MegaSquirts out there say volumes to me about real-world experience.   Probably more relevant is Per Andersens MegaSquirtAVR (who developed the targetAFR code) and MegaSquirt TomTek who does a lot of work with WB02, ignition and ion sensing.

-Peter
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