Date:         Sat, 3 Feb 1996 20:43:39 CST6CDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Dan Houg" <fairwind@northernnet.com>
Subject:      Air Flow Meter /part 2

Just thought i would report on the status of my dinking around with 
the AFM on my '87...

The van continues to run nicely.  It must have been the dirty 
contactor in the AFM that was causing my gremlins.  and now, for the 
rest of the story...

I had tightened the tension on the spring acting on the air vane.  
This has the effect of leaning out the basic setting because with 
more spring tension, there is less air vane movement.  It works 
dramatically and should not be indescriminately fooled with.  A long 
(in terms of email volume) time ago, i had posted a 'wasserboxer tune-
up report' that detailed a lingering problem my tune-up did not 
solve.  Namely, a rough idle on initial start-up but only lasting
a minute or two.  Paying attention to this miss, i felt it was caused 
by over-rich mixture due to the black soot specks left on the snow.  
With the 'leaned out' AFM, this miss is nearly gone.  in fact it just 
seems like a few sputters associated with starting any motor at -20F.

Here's my Theory.....  (why do i feel the need to explain these gifts 
from the gods?)

On start up, a cold engine is regulated by a prescribed set of fuel 
and ignition patterns programmed into the ECU given specific inputs 
from the coolant sensor, the air temp sensor, and the air flow meter. 
 There is no feedback from the O2 sensor until it reaches its 
critical temp of about 600F.  This is called open loop mode and only 
lasts for a minute or two until things heat up.  If the AFM is 
sending a signal saying the air vane is moved X amount, it dumps that 
amount of fuel in.  AFM set rich = rich running until the O2 sensor 
heats up enough to wake up and tell the ECU to lean things out.  Make 
sense?

Remember that Gary Larson cartoon where the mathematician is deriving 
this huge equation on the black board and then writes "Then a miracle 
occurs." and finishes the derivation?  That's how i'm begining to 
feel about electronic engine controls.  We work with a known and 
measureable set of constructs; the various sensor inputs, grounds, 
wiring, and controlled devices.  All well defined and operate in a 
predictable fashion allowing successful troubleshooting if we are 
knowledgeable (and damn lucky sometimes).  But then a miracle occurs. 
 The ECU.  The bugger literally comes in a black box and by its very 
nature of being unknown, offers a degree of randomness that 
undermines my confidence.  It is always suspect... what if it has a 
glitch in it?  a bad solder joint. a demon to be exorcised.  its 
presence erodes the soul.

When the Big One goes off because some syphillitic third-world leader 
pushed a mushroom-cloud shaped button, few things in our modern world 
will be left functional.  Nearly everything has a tiny, fragile, 
utterly mysterious little black IC chip in it that will crackle like 
fresh Rice Crispies.  We'll be left in a world with cock roaches 
pre-electronic ignition busses. Unfortunately, my roto-tiller will be 
the only thing *i* have left working....

-dan (who perhaps shouldn't have had that last glass of wine)