Tas,
I am amazed by the depth of your thinking. The textbooks say that EGR shortens ignition delay.
I haven't played with fuel economy since the experiments last summer. My normal procedure was to fill my tank to the neck at the Tooele truck stop area on I-80, west of Salt Lake City. I drive west to the Nevada line (Wendover) 100 miles, then turn around and drive back to the truck stop and refill. All on cruise except the start, stop, and turnaround. The highway is nearly flat and usually has very light traffic. I monitor my speed with a GPS, and use GPS for distance. I also drive fast for one hour before beginning the test. Results are fairly reproducible, about +/- 1 mpg (in 65).
My scan guage is running during the testing. Here is something to ponder. About 10 miles out of the truck stop, the highway pavement changes from smooth concrete to smooth asphalt. I see an abrupt drop in fuel economy on the ScanGuage when I transition from concrete to asphalt, maybe a few mpg.
On a trip near the bay area in California, I crossed a pavement change where I-580 connects to I-5. I-580 is smooth concrete and I-5 is rough asphalt. My ScanGuage reading dropped by about 10 mpg. Repeat: From about 75 mpg to about 65 mpg--about a 15% difference due to pavement change from smooth concrete to rough asphalt. This effect has been documented by others.
Ernie
Quote:
Originally Posted by tasdrouille
Ernie, when you say you worked with kerma to chip your TDI for fuel economy, how did you measured fuel economy when making changes to the ECU maps?
Using vag-com to log fuel consumption, my experience has been that advancing start of injection timing 3 degrees over stock (everything else remaining the same) led to more or less 5% increase in FE.
Tweaking the EGR for max recirculation also lead to an additional 3-5% in FE when combined to a 6 degrees timing advance over stock. When using vag-com or a scangauge to read fuel consumption, increasing EGR will look like fuel consumption went up, because the IQ value was offset upward when you change the EGR rate, which is deceptive, you need to look at tank-to-tank FE. Also, since increased EGR retards the start of combustion event, you need to advance the start of injection timing in order to preserve optimal FE.
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