[Diy_efi] Importance of TPS with lightweight cars

[Shannen Durphey]

Djfreggens at aol.com wrote:
 
> > 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.  
> 
> no it most likely has to do with driving up nox2 emmision.

The "removal" of highway fuel has everything to do with increased
emissions.  The drive cycle for emissions testing did not cause the ecm
to enter highway fuel mode.  Therefore, a vehicle could be calibrated to
pass emissions testing and achieve increased fuel economy at the same
time.  While emissions may seem to be priority number one, CAFE
noncompliance gets extremely expensive in a hurry.  Vehicles such as the
Caprice, the Corvette, and the Camaro needed as much help as possible to
bring the corporate fleet mileage within the legal limit.  Just as the
rapid drop in numeric final drive ratio in the late '70's and early '80s
was a quick fix to decrease the tailpipe emissions in parts per mile,
highway fuel mode was a patch for improving corporate average fuel
economy in the middle '80s and early '90s.  Once the EPA realized what
was going on, they shut it down.

The EPA isn't on top of everything that happens.  Remember how long it
took before they caught Cadillac dumping excess fuel into the tailpipe
in the case of excessive engine temps?  Hefty fines were given out
several years after the fact.

Shannen

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