Bosch Motronic AFM => Point - Counterpoint

[WERNER_HAUSSMANN at HP-Loveland-om2.om.hp.com]

I think both views are correct in the point counterpoint.


Most EFI systems do NOT run at closed loop (Stoichiometric) unde
r heavy 
load or WOT.  At this time loosening the Air Meter will richen t
he mixture.

Some older EFI systems and many DIY systems do not run closed lo
op at all, 
and for these the 'spring' allows for fine tuning the AF ratio. 
There are 
other ways and this is one that works.

For the Bosch systems with the air meter, when changing the trot
tle, the 
air meter will overshoot, the ECU will sense the rate of change 
and and 
provide an accelerator pump action. 'Loosening the spring' will 
increase 
that accelerator pump action. That is kind of the intend of the 
discussion.

Using the coolent sensor is not as good because the cooling temp
erature is 
not stable.  Using the air temperature sensor in the Air meter i
s another 
way to make small adjustments.



Werner


______________________________ Reply Separator _________________
________________
Subject: RE: Bosch Motronic AFM  => Point - Counterpoint
Author:  Non-HP-owner-diy-efi (owner-diy_efi at coulomb.eng.ohio-st
ate.edu) at 
HP-ColSprings,uugw2
Date:    6/26/96 8:01 AM


At the risk of continuing this discussion into the new millenniu
m, I present 
this response from Pat Braden, author of the book "The Alfa Rome
o
Owners' Bible", in response to our recent discussion.

  ************************* Forwarded Text *********************
*********

"2-3 notches on the spring will change the Air Fuel ratio by abo
ut 2%"

Hate to disagree. Presuming that the spring has any effect on ai
r/fuel 
ratio, loosening it (that is, allowing more air to enter) would 
_lean_ the 
mixture, not richen it. Conceivably, weakening the spring could 
allow the 
flapper valve to swing further for a given air velocity, indicat
ing a 
higher volume of air, for which the control module would immedia
tely 
provide a richer mixture. However, the mixture would immediately
 be 
corrected to the stoichiometric value of about 13.4:1 by the con
trol 
module, acting on information from the Oxygen sensor.
My understanding of the system is that the spring is there only 
to return 
the flapper and act as a damper on its actions. Weakening the sp
ring 
reduces the damping effect, allowing a faster throttle response 
but not 
changing the A/F ratio.

With any Motronic system, presuming it is in working order, noth
ing you
do to the mixture will change the actual air/fuel ratio because 
the Oxygen 
sensor signal will simply force the control module to correct th
e mixture 
strength to stoichiometery. With the Oxygen sensor disabled, the
 easiest 
way to get a richer mixture is to fool the coolant temperature s
ensor  by 
putting resistance in line.