[Diy_efi] Importance of TPS with lightweight cars

Shannen Durphey shannen at grolen.com
Mon Jan 13 11:31:25 GMT 2003



William Shurvinton wrote:
> 
> ----- Original Message -----
> From: "Shannen Durphey" <shannen at grolen.com>
> >
> > GM did this for several years with light vehicles (pickup trucks did not
> > get this type of tuning).  I have done this in my own cars for almost 15
> > years.  The trick is to understand when it's possible to operate lean,
> > and when to back out.  For anyone who is not mild on the throttle, it
> > works out that much less than "most of the range" becomes a lean fuel
> > mode.
> >
> > Look at the hac for the 727/730 calibration.  Read through 'til you find
> > the highway fuel mode sections to get a rough idea when one of the big
> > three automakers felt it was ok to run lean.
> 
> I have looked at this a few times, but seems a bit slow, plus needs VSS,
> which I don't yet have. I was approaching from the other direction,
> asssuming lean more than normal and correcting with PE. Will re-read the
> code again and think some more.

Some things to think about:

How will you determine where it is ok to run leaner than stoich?  
How did GM make this determination?

AE has one job:  covering the "hole" created by rapidly opening the
throttle.  It's not to be used to cover anything else.  In GM cals AE is
not scaled, but is a time based value.  It is more difficult to get
correct AE values than close AE values.

With GM, PE is designed to add fuel and/or spark.  PE mode can be used
primarily to provide cooling and initiated by counting a timer down to
PE enable.   It can also be used as the basis for acceleration and WOT
modes by engaging it under any substantial load.  This might be
equivalent to adjusting the secondaries on a two stage carb system.  Or
it can be disabled entirely.  

A fuel map can be made that is leaner than stoich during low load
conditions, and leaner than best power under acceleration.  This can be
combined with a spark map that is less aggressive during non PE
operation.   PE can be adjusted to provide maximum acceleration.  PE
enable parameters can be adjusted to suit your tastes from there. 

With my cars, most of my driving is on the highway.  Except when I'm
playing around, most of the time I drive on the highway throttle opening
is less than 25%.  If I can remove some fuel from the map in these
conditions, then I can run lean(er) "most of the time."  I make sure to
increase PE responsiveness and if the engine demands it I also increase
the AE fuel delivered.

Shannen

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi



More information about the Diy_efi mailing list