Re: was resistor in the O2 loop now AFM flap shennanigans

[Rob Ellis <aellis@xxxxxxxxxxxxxxxx>]

Well, I thought this was well-known, but a lot of people have 
asked about it.  First off, don't expect a miracle here.  This 
mod is a fine-tuning of the fuel system, the difference this 
makes will depend greatly on the other mods which have been done.

Also, do this at your own risk... you can damage the AFM, or your 
cat, the engine, fail emissions specs., etc.

Remove the square black cap of the AFM (it's held by an adhesive 
sealant) and underneath you'll find some electronics, and a black 
gear.  A metal "finger" is located in a valley of the gear teeth 
(it's a good idea to mark this valley with a Sharpie).  Push the 
finger to the side, and turn the gear a notch or two at a time 
ONLY.  I may be wrong here, but IIRC, Counter-Clockwise gives 
richer mix, Clockwise gives leaner mix.

Theory: You're changing the tension of the flap, making it easier 
or harder for air to open the flap.  The computer reads how far 
the flap is open, and adjusts the fuel accordingly.  If the flap 
opens easier, then more gas will be added to the mix, since the 
computer thinks more air is coming in.

That's it.  Be sure to test this with either an exhaust analyser 
(your local shop), an air/fuel mixture meter (~$60), or on a 
dyno.  Or you can use a fancy multimeter with an averaging 
function, and check the AVERAGE value of the O2 sensor output.

For reference:
Maximum power occurs at 12.6:1 (Labmda=0.86) A/F ratio
Stoichiometric occurs at 14.7:1 (Lambda=1) A/F ratio
Maximum fuel economy occurs at 15.4:1 (Lambda=1.05) A/F ratio

I think you should be able to reach max power by moving only 2 or 
3 notches on the gear (depends on the engine).

Good luck, and I hope this helps!

Rob

> Date: Mon, 13 Jan 2003 12:58:05 -0500
> From: "Ric" <rlb1@domain.elided>
> Subject: Re:was resistor in the O2 loop now AFM flap shennanigans
> 
> ROB Wrote>>>>>
> 
> However, there are better (and easier) ways to do this... for
> example,
> adjusting the tension on the AFM flap by a few notches will give
> you a
> nice, fine adjustment of the fuel mixture (at least on older
> cars, like
> my E30).
> 
> 
> 
> Can you tell us more about this or point us in the right
> direction?
> 
> Ric
> 1991 318is

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