Some ideas...

[p.beaubien1 at genie.geis.com]

Dale,
 
  > S-D is more reliable. You also need to calibrate both of them, no matter
  > what, since MAF has to calculate reversion.
 
Isn't S-D a lot more complicated to calibrate (ie. map)? Reversion is when
you basically get a standing wave in the intake or exhuast pipes, correct?
You'd have to account for that in a SD system as well, correct? Does
reversion show up as a dip on a VE graph of an engine?
 
  > A GM MAF sensor gives a frequency output, which can be measured using an
  > input capture function on the 68HC11.  >
 
What other smarts are built into this GM MAF sensor. I take it not all GM's
use this type of MAF sensor. Do you know which ones do? Is the frequency
directly proportional to the amount of air passing through?
 
  > If you know the speed of the engine, degrees can be translated into
  > timer ticks, which is how most engine computers do it. For example,  a
  > timer tick is 250 usec on my ECM, so if it takes 12000 timer ticks per
  > cylinder on a 4-cylinder.... well, you can easily figure out speed with
  > a division, and the spark angle is translated to, perhaps, 10000 ticks
  > after the first reference.
 
How accurate is this when the engine is accelerating? I guess good enough.
It sounds like you've built a little something; can you share what you've
done?
 
  > If you want to use a 68332 processor, you *could* use a degree wheel,
  > becuase  in a 68HC11, the processing overhead of too many ticks can get
  > heavy. I  found that more than 8 ticks per revolution tends to slow
  > things down  too much.
 
Which are you using? So you think that it's better to have a few (say 4)
ticks/rev and interpolate the position of the engine rather than have a
bunch of ticks/rev knowing basically where the engine is.
 
  > You sound like you're kinda on the right track. The biggest thing is
  > different processors have different timers, so the HC11, which is
  > useful for almost all ECM needs, lacks in here...  the 68332 series
  > looks NICE. I was going to try one...
 
What I'd like to do is hook up the sensors on the engine and then be able to
monitor them. Then I'd get into have a microprocessor actually control bits
and pieces until it can handle most everything. Once I get some sensors
connected etc., I'll think more about which processor I'll use.
 
Thanks for your help.
 
 
Matt.