Is it possible to re-write the cruise control programming to read from the TPS signal instead of the VSS signal?
The thinking is this: Currently, the cruise maintains a constant speed by taking a reading from the VSS and modulating the throttle to match that signal. On anything other than a perfectly flat stretch of road, this constantly adjusts the throttle position, increasing/decreasing the injector pulse, and often putting the engine into boost. As we all know, more boost = more fuel consumption.
However, if the cruise system were reading off the TPS, I think it would effectively "lock" the throttle in a fixed position. This would eliminate the extra fuel pulses from the injectors, keep the engine out of boost, and should increase fuel mileage considerably. Yes, you would lose speed going uphill, but you would regain it on the other side, and your speed would average out over time. Wind resistance would also be another factor.
Case in point: When my Charger (no cruise) still had a functioning odometer, with mostly highway driving such as my commute to work, it would average right around 30-31 mpg. My best for the car was on the way back from SDAC-21 between west of Chicago and Iowa City, which is a very long flat stretch of road, where I managed 34.1 mpg without doing anything special other than maintaining speed. The following year, my Daytona (regularly 28-30 mpg hwy) reached that same mileage on that same stretch of road, with the cruise control on.
Thoughts?