RE: 87 535is is running lean

[Jerry Lee <Jerry.Lee@xxxxxxxxxxx>]

Bob,

Having gone thru way, way too many problems with engine management (read
motronic) problems with my '88-535is and emissions certification in Atlanta,
I can tell you for a fact that the O2 sensor (working correctly) will indeed
try to lean out mixture, especially at idle.  All of these cars run great in
the open look mode.  I have a few questions: Have you invested in the Robert
Bentley E-28 manual?. Are you running the proper Bosch Silber Plugs? How
many miles are on you 5er?  Have you checked the exhaust system from the
manifold to the converter for leaks? 
Even a slight leak will cause an improper reading at the O2 sensor, and the
computer will compensate by driving the mixture lean.  A slight AFM
adjustment (I have a test mule and a new adjusted replacement unit) by
"loosening" the spring (make sure that you make an index mark on the toothed
wheel) 1 to 2 'teeth" should give you better driveablilty, and high mileage
cars they tend to lean out as they get older. Take note that this will do
nothing for your idle in the "closed loop" mode (O2 sensor connected, car
warm to hot).  Make sure that you check the fuel system for correct pressure
and delivery, and that the pressure regulator is working properly (this one
part made a nice improvement).  I know, there  lots of stuff to check, but
these cars run very lean from the factory, and this version of the motronic
system is hard to diagnose correctly.  Use the manual, verify everything.
It took over 5 months of on and  off work to get my high mileage 535is, now
@ 182Kmiles, to run perfectly.  Have you had the FI system cleaned?  If not,
start using the Red Line S1 synthetic fuel system cleaner, it will run
better each tank until the deposits are cleaned off the back of the intake
valves.  FWIW: You might also look into a Jim Comforti chip, it was night
and day difference in my car: more power, higher rev limiter, better fuel
curve, better starting....

I hope that this helps,
Jerry Lee
'88-535is, 182k, JimC, Borbet 16x7.5, H&Rs, B-Sports, much, much more...
'71 Dodge Challenger R/T, 425 hp, pistol grip 4 speed, 3.23 posi, 1 belt
beast..
'96 C-1500,Ext-Cab,Vortec 350, trailer pkg tow-mobile..
BMWCCA # 150271



<Date: Thu, 17 Jun 1999 10:57:36 EDT
<From: BOBINYELM@domain.elided
<Subject: Re: AFM Recalibration

<My 87 535is is running lean. Idle is rough and car hesitates and lacks
proper 
<power. By substituting all parts in the injection system, I found a
computer 
<(059 style on this model) that is 75% better, but the car still runs better

<if the AFM flap is opened slightly manually and the O2 sensor is
disconnected.

<I have read that recalibrating the AFM spring weaker by one or more notches

<will richen the mixture to where the car will run right.

<My question is if the O2 sensor is reattached, won't it try to drive the 
<mixture back too lean by compensating on injector pulse width?  Anyone 
<recalibrate with success?

<Thanks,
<Bob

------------------------------