MAF meters and open-loop.ABout

[Roger Heflin]

On Thu, 25 Feb 1999, Daniel Houlton wrote:

> Jason_Leone at amat.com wrote:
> >
> > <<So maybe it is stopping at 5 volts and can't go any higher with more air
> > flowing through it?>>
> >
> > You answered your own question. The Mass Air system is not ideal for
> > forced-induction. In fact, it's pretty damn limiting. The MAF sensor can
> > only put out 5V and that's it. It's really easy to max it out when you blow
> > through more air, and even draw through more air. It just depends on the
> > MAF housing diameter,intake plumbing of the vehicle, turbo characteristics,
> > and the air flow velocity that cooling the MAF platinum wire.
> 
> I did some tests last night.  From what I remeber of monitoring the MAF
> output pre-turbo, I think the highest voltage I got was around 4.1v and
> that was always a spike when I nailed it.  About 3.8v was the steady
> state WOT voltage.
> 
> I did the same tests last night with the turbo.  Under boost (max about
> 7 psi) and WOT, the highest reading I got was around 4.3v and again that
> was a spike.  Also, the lean cut out I described before seemed to happen
> right around 4.0v.  Under 5 lbs boost, the voltage would stay just under 
> 4.0v and going a little further with the throttle to trigger the WOT
> switch would send it up to about 4.1v or so and it would go lean.  The
> 4.3v spike I got was hitting WOT (going from about 5 lbs boost to 7)
> for about one second (before backing off because it was lean).
> 
> So, it appears that the MAF isn't necessarilly maxing out.  Maybe the
> computer is?  i.e. 6 lbs of boost @ 5000 rpm is about 45 - 50 hp more
> (mathematically anyways) than the computer expects it can ever produce.
> Maybe it ignores the higher MAF readings because it knows it shouldn't   
> ever read that high?

I don't know about the computer in your car, but in mine (93 Z28, GM
computer) there are limits on several of the sensors after which the
computer takes a default value, because it believes the real value
must be wrong..  I don't know if you are hitting that, but that is an
option on some vehicles.  If you had a scan tool hooked up, it would
probably show odd things if this were happening.  Of course if it hit
the limit I would expect it to set some sort of code in the computer.

				Roger