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From digest.v7.n902 Thu Jan 8 14:47:14 1998
From: (Eric Tangen)
Date: Thu, 8 Jan 1998 11:08:51 -0600
Subject: <M30> Re: Big 6 air flow meter tinkering

>From: "John G.Burns" <>
>Date: Thu, 08 Jan 1998 0:10:37 GMT
>Subject: <M30> Re: Big 6 air flow meter tinkering
>I have read of the need for this procedure in the BMW
>Enthusiasts Companion p93. It says that "BMW Fuel Injection:
>An Enlightened Approach" contains the details of how to do
>this "straightforward" procedure.
>I have an '85 635CSi with 142K and am respobsible for two
>friends 520i's which both have over 100K. In one 520 the
>idle adjust screw has bottomed out which I believe is the
>sign that spring retensioning time has arrived. Any adivce
>is appreciated.

is 'BMW FI: AEA' still in print? i'm pretty sure it isn't; mine is a spiral bound book from Metric Mechanic and covers only K and L Jetronic.

the AFM recal is pretty straightforward; you add tension to the spring to lean out the mixture, release the spring to richen. spring tension cal works across entire rev range, CO scew adjust affects only the idle mixture. Back it out to lean, screw it in to richen.


0. get spark system in order before doing

anything on the fuel system.

  1. paint a dot on the spring wheel and

    a corresponding dot on the AFM body; this is helpful if the spring spins wildly during adjustment.

  2. ajust richness/leaness at 2500-3K RPMs

    by pressing the flapper which moves the pointer on the wiper track; monitor the O2 sensor to see how much adjustment you need and change spring tension accordingly. one tooth at a time is best.

on my L-jet cars, i do this with 02 sensor open loop; i have no idea how a Motronic car responds to open loop O2 operation.

'BMW FI: AEA' recommends finding
this sweet spot by ear.

3. i thought the early Motronic cars had

a dip switch in the control unit
for minor adjustments to the richness and spark advance; i've heard this referred to as the 'Fuel Quality Switch'. that's all i know about it

eric tangen
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