MAF Sensors and Re:Spell Check

[Mark Boxsell]

At 10:46 AM 7/02/96 EST, you wrote:
>Alain Marchildon wrote:
>
>>OK 
>>The bickering has went on long enough.
>>I will reply be my self.
>>And terminate it my self.
>
>Time to throw my 2 cents in - 
>As a third generation American of French Canadian decent, give the guy a break!
>
>Alain, c'est ne pas votre probleme, ca va?  :-{)>
>
>Sometimes *I* write worse in English.  Maybe it's in our genes.
>
>
>Getting back to DIY_EFI, does anyone have more information, including the 
>governing equations on hot-wire mass air flow sensors - I may have to work one 
>up for my Briggs & Stratton project.  Single cylinder engines (especially 
>leaky flatheads like the B&S) have a horrible (to non-existent) vacuum signal
>to work with, and I'm not likely to find a MAF sensor with a 1" throat at my 
>Ford dealer.  Since the system I'm designing needs to be altitude sensitive, a 
>MAF may be a better approach.  The original plan was to use MAP and gather data
>on the test stand, but time is getting short and a MAF interfaced to a lookup
>table may be a far better choice than a MAP that may be reading noise.
>
>I'm assuming that the MAF hot wire is fed with a constant current and the 
>voltage variation due to temperature-dependent change of resistance is the 
>output that is conditioned further.  If anyone has any more info it would be
>much appreciated.
>
>
>MAP - Manifold Absolute Pressure
>MAF - Mass Air Flow
>B&S - Briggs & Stratton, maker of most of the world's lawn mower engines.
>
>
>Cliff Ducharme
>                                         /
>"A wing and a prayer"           _______[*]_______
>                                    b  /    d
>
>
>My remarks do not reflect the opinions of my employer.
>

Cliff,
      use throttle position it will work fine. You will still have to "map"
throttle position verses RPM of course. For altitude use a map sensor (eg GM
style) (don't connect to the manifold, don't even use a hose on it) and
apply a separate correction after you have looked up the value in the "map".
Using a Briggs & Stratton is a bit of a worry we use those things for boat
anchors in Australia (although I must conceed that their newer engines are
much better). Why not a nice Honda or Mitsubishi stationary engine.
You are wasting your time with MAF on a single cylinder engine because of
the pulsing in the inlet.
I have heard a lot of talk (on this list) about MAF sensors but until you
have to apply them they sound easy however you have all sorts of problems
with pulsing and reverse flow, etc. Why do you think some of the
manufacturers have such elaborate ducting and air cleaners (air box) that
look like they came off the space shuttle!
Don't get me wrong I have nothing against MAF but it's the same old story
things are not as easy as they may first appear.
This reminds me of a guy who had an early Air Sensors system (this was about
7 years ago)on a Mitsubishi Starion Group A car and wondered why the thing
would go bulk rich on gear changes and blow a puff of smoke and carry on
when he put his foot down again.
The Air Sensors system (which uses MAF) was happily injecting the correct
amount of fuel for all the air that was going out the compressor bypass
valve!!!!

A word for Peter Wales. I been told we don't use the "Queen's english" down
under but everyone seems to understand what I'm saying!

                regards,
                         Mark Boxsell
                         MRB Design
                         Sydney  Australia