[Diy_efi] Importance of TPS with lightweight cars

[Shannen Durphey]

Adam Wade wrote:

> --- William Shurvinton <shurvinton at orange.net> wrote:

> Makes me wonder if the tuning strategy shouldn't be to lean off as far as
> possible through most of the range and then have a fairly agressive
> acceleration and PE strategy  to handle when you open out the throttle.

> > Not with cars, but plenty with motorcycles.

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.

Rumor has it that the main reason highway mode was discontinued is that
it was found out by the EPA and determined to be a type of emissions
defeat device.  There are several mentions of highway fuel mode in the
archives.  I'm sure some of them cover the approach you mention.


> Seems like the more responsiveness the engine/vehicle
> combination has (lightweight, easy-revving motor
> combines with light chassis), the LESS it needs
> acceleration mapping, because it can accelerate enough
> to keep intake air velocity up.  Like with starting
> issues, the big problem seems to be when intake
> velocity drops.

Like bike engines, large and heavy industrial engines with governors
often have no acceleration pump or no acceleration aids.  Not being
subject to large and rapid changes in rpm or throttle opening, they have
little need for additional enrichment devices.

Shannen

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