UEGO IDEA

[Ludis Langens]

I wrote:
> I checked the VE table in a production PROM.  At most RPM values, there
> was almost exactly a factor of two increase in VE from 20 KPa to 100
> KPa.  (Once the MAP gets multiplied in, that means a factor of ten in
> fuel from 20 KPa to 100 KPa.)  Across the RPM range, the highest and
> lowest VEs varied by about a factor of 1.5.

Oops!  I forgot that the VE is actually the sum of two tables - one
which I looked at for the above, and one which expands the first for
high RPMs.  The actual ratios are much smaller than above.  Here are the
corrected values:  The VE at 20 KPa is about 2/3 that at 100 KPa.  And
the VE at low RPM is about 80% of that at peak torque RPM.


Stuart Bunning <stuart at kenelec.com.au> wrote:
> Is the A/F ratio table found at xC4FA (ASBX) in my memcal responsible for
> part of the fuel supply multiplications that would be experienced even with
> a totally
> flat VE table?  As my initial thought was if VE was flat it would lean out
> as load or RPM increased. 

Yes, your A/F ratio table also affects the amount of fuel.  However,
that table's purpose is not to characterize the engine.  Instead it is
to select when to go into PowerEnrichment mode, and how much PE to do. 
Some older ECMs use just a single constant instead of a whole table like yours.

The VE tables let your ECM compute the amount of air flow into the
engine.  In a hypothetical system, the A/F ratio could be built into
that table.  However, knowing the air flow by itself can be useful for
things like EGR.  Further, when the engine is cold, the A/F table may
get ignored because the ECM is using a cold start A/F table.  The VE
needs to be broken out seperately in this case.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/