[Diy_efi] pic based afm -> maf conversion

Daniel R. Nicoson A6intruder
Thu Jan 19 02:37:29 UTC 2006


Honestly?  With some of the stuff you are proposing, I think you'd be
further ahead trying to read the bin file off the BMW ECU and figure out all
the settings there.  Then modify the fuel tables, spark tables, airflow
functions, and write this info back to the ECU.  What you are proposing in
all this discussion so far is modifying inputs to achieve outputs.  Problem
with that is you don't really know what the ECU does with all that.

One example:  You mentioned adding a lean-burn cruise mode.  I assume you
intend to tell the ECU there is less air than normal so it cuts fuel back =
lean.  That would be good except for cruise is typically a closed loop
operation.  Not sure how old your ECU is (do tell) but since the mid 1980's
most ECU's run closed loop at cruise which means they look at the calculated
air coming in, factor in other things like RPM etc, command a pulse width
and then check the result (O2 sensors).  Now if they detect a bit of
leaning, the ECU modifies its short term fuel trim table and starts the loop
again, this time zeroing out your recently added "lean input".

So by just modifying the inputs, you won't achieve long term success.
Without control over the actual code, tables, functions and scalars, most of
your proposed mods will not work.

This post is not meant to discourage you in your quest to make the BMW
better.  I would first research how much is known about the actual operating
logic for this particular ECU.  I think the older Motronic ECU's may have
some hacker groups out there, find them, learn as much about the various
modes of operation, then consider what some of these "input mods" will
really do.

Dan Nicoson

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