Quote:
Originally Posted by bwilson4web
I noticed the initial fuel consumption was quite low at idle after running at highway speeds and parking but after a few minutes, I could see the spark retard and fuel consumption increase. This MAY be due to the intake manifold cooling off and thus cooler air. However, I have not yet studied this effect. Given the Prius normally turns the engine off rather than idle with the engine running, it may be moot.
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I think you have part of that backwards after getting off the HW the engine (when running) should be at the lowest fully warmed up temp. Once the car stops the intake manifold now has less air moving around it and the engine holding more heat in the engine bay causing it to heat soak. From this heat soak the IAT (intake air temp) will read higher and the coolant will get warmer. On all the PCMs I have looked at as IAT rises it subtracts timing when it is lower it adds timing usually there is a flat spot that 0 is added to the timing. The same goes for coolant temp but also scales it with RPM or AirMass instead of just temp.
So with that said I believe that the resistor is used to A. Set a single cold value to increase timing or B. Placed parallel with the sensor to give a reduced IAT value to add timing.
Some people tuning cars will place a variable resistor in place of the sensor and use that to add or subtract timing on the fly.