[Diy_efi] Re: Diy_efi Digest, Vol 4, Issue 30

[Adam Wade]

--- Bill Washington <bill.washington at nec.com.au>
wrote:

> but when they are working I believe they do measure
> the mass flow.

If that was true, then there would have been no
purpose for an ambient air temperature sensor, which
many if not most of the VAF L-Jet derivatives have. 
There would also have been no reason to build the
expensive and difficult early hot-wire MAF sensors
used in the LH-Jet and early Motronic units.

> Then the O2 sensor can correct for the 
> inaccuracies...

The O2 sensor is for closed-loop operation, and not
for correcting anything in open-loop operation.

> The Hot wire Mass flow meter (LH Jet) is a
> refinement which overcomes most of these issues.

The hot wire MAF has all kinds of problems with dirt
and getting an accurate sampling of airflow, not to
mention counting reversion as additional airflow and
running pig-rich unless mapped to handle areas where
reversion occurs.  These problems were not wholly
overcome until the unidirectional hot film element MAF
sensor, which still has some problem with accurate
sampling of airflow.

Since it is a much more expensive and
difficult-to-manage sensor, why would anyone have
bothered using it if, as you suggest, the VAF was
wholly adequate for measuring air mass, and the O2
sensor corrected for any inaccuracies in the VAF's measurement?

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