MAF meters and open-loop

[d houlton x0710]

Bruce Plecan wrote:
> 
> 
> From: Daniel Houlton <houlster at user2.inficad.com>
> To: EFI <diy_efi at efi332.eng.ohio-state.edu>
> Date: Thursday, February 25, 1999 8:06 PM
> Subject: Re: MAF meters and open-loop
> 
> Please read the archives about O2 sensors, and EGOR before melting your
> motor.
> Unless your oem O2 is WB it's not telling you what is really going on.

Nope, it's not a WB and I have scoured the archives about 02 sensors so
I'm familiar with it's really telling me (or not actually).  My understanding
of how these meters work is they can only reliably show rich or lean.  Not 
*how* rich or lean.  The LED's up and down the range I assume are buffered
and kind of represent a duty cycle.  It the mix is above .5v (rich) for say
70% of the time, then 7 LEDs light up.  If it's 50/50 above and below .5v,
it shows 5 LEDs, etc.  It can give you an approximation of how rich or lean,
but not the true value.  If this isn't right, please let me know.

I had asked about an EGT gauge.  Would this be the best way to monitor what's
happening to prevent a melted piston?  Seems like it would be since A/F
mixture isn't the only thing that can cause a melted piston.  Things like
intake temp (high for me under boost without an IC) can cause a lean mixture
(or even a stoich mix?) to burn a piston a lot easier/sooner than normal
intake temps right?  Seems like exhaust temp is going to be directly related
to how much heat the pistons are seeing regardless of A/F mix or intake temp.
Does AutoMeter make an UltraLite series EGT?


> Are you absolutely sure your MAF is variable voltage and not variable
> frequency?.

Variable frequency?  I'm not sure.  Would I need an o-scope to see this?
Variable voltage?  Definitely, and it's very much determined by load on the
engine.  It seems to be quite non-scalar though.  Very slight changes in
load at idle and light cruise result in big changes between about 1v and
3.5v.  The higher the load, the slower the output voltage climbs.  From
light cruise to WOT the output voltage only goes from around 3.5v to just
over 4v.

--Dan