[alfa] Re: alfa-digest V9 #1193

[alfa@xxxxxxxxx]

> Date: Thu, 18 Mar 2004 13:42:16 +1100
> From: dmasters@domain.elided
> Subject: [alfa] tuning/driving meter - was AD V9 1191
> 
> Can you answer a few questions about the tuning of my stock Alfa75 Twin
> Spark? These motors must be very similar to the Spiders with their variable
> intake cam.
> 1.  For years I have been running a DVM across some wires connected to the
> O2 sensor, and I like to make sure that the reading oscillates around 0.5V
> all the time at cruise.  I have adjusted the control on the AFM to see what
> difference it makes.  I count the turns.  For a Motronic 4.1 system, is
> this a valid way to set mixture?

It's a valid way to adjust the mixture, yes.  But I bet you are not seeing much
result on the O2 sensor.  Under the nominal conditions, it will always try to
center on a stoichiometry point.  Seeing what you are doing at air flows where
the computer does not use the sensor would require an additional WB sensor. 
That, and while I know that is one way to adjust, I can't tell you which way
goes more or less.  For that matter, I think you are adjusting the bypass flow
around the sensor- which is leakage air, and will not overly change the mixture
at high air flows.  But that last part is a guess.


> 2.  Will Tech Edge or Megasquirt help me here, or is my real issue that I
> need a real exhaust gas analyser to ensure a good mixture.  The few times I
> have had the car to a Dyno for checking, the mixture has not needed to be
> adjusted, but I do wonder about it from time to time.  There is so little
> to adjust, it seems to be more a matter of keeping everything clean and
> replacing failed sensors.
>

Either system will control the a/f, but may not control the VCT system.  You
mention that you are worried about it- in what way?  Generally, the do drift
over time, but there are also learning algorithms to remember where you are. 
Also, at peak air flow, I would imagine your car runs on the rich side, since
it has to protect the catalyst from damage.  So there isn't much fear of poking
holes in things.  The Motronic system does a very good job at controlling fuel,
air, spark, a/c, idle, vct...  If you are not going crazy with the mods, why
mess with it?

Eric Storhok
AA 
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