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Old 03-03-2016, 09:04 PM   #37 (permalink)
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Join Date: Feb 2011
Location: Phillips, WI
Posts: 982

Nameless - '06 GMC Canyon
90 day: 37.45 mpg (US)
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Revision H: Vacuum gauge

My winter 2015-2016 results are in: 3180.0 miles, 100.16 gallons = 31.75 MPG. This is by far the best winter mileage I have ever got with this truck. My best previous winter mileage was 30.08 MPG. This winter was warmer than average, which I estimate accounts for about 0.5 MPG.

The remaining improvement came from learning how to work with the engine control system. I have a Scangauge and a mechanical vacuum gauge. I noticed that, at 55 MPH (1800 RPM) and 10 In Hg vacuum, the instantaneous mileage could be either 22 or 25. Then I noticed that the instantaneous mileage under those conditions was 25 if I was slowly increasing throttle from about 13-14 In Hg vacuum, and 22 if I was decreasing throttle from 5-9 In Hg vacuum.

Similarly, MPG at 15 In Hg can be 35 to 45. If I very lowly close the throttle to 15 In Hg, it shows 35 to 38 MPG. If I close the throttle at a moderate rate to 15 In Hg AND the speed at 15 In Hg increases by 1.5 to 2 MPH, the instantaneous MPG increases to 42 to 45.

My current technique in rolling hills is to climb at 5 In Hg, get to 55 MPH at the top, then back off to 15 In Hg, let the speed pick up, and watch the MPG climb. When the speed decays to 55 MPH at the bottom, I will slowly open throttle to about 10.5 In Hg at 27 MPG until the speed starts to drop, then go straight to 5 In Hg.

I think what is happening here is that the cam timing has hysteresis in its programming with a switching point around 10 In Hg, and another switching point near 15 In Hg combined with a speed rate of change factor. Whether true or not, my mileage this winter was 5.6% better than I have ever done in winter.

(1-31-2017) Link to my vacuum gauge thread:

(2-1-2017) Summary of MPG results:
Summer 2013: 36.0 MPG
Winter 2013-14: 28.7 MPG
Added the vacuum gauge
Summer 2014: 38.2 MPG
Winter 2014-15: 30.0 MPG
Summer 2015: 38.5 MPG Had wheel covers this summer
Winter 2015-16: 31.75 MPG This winter was warmer than normal
Summer 2016: 38.6 MPG

The vacuum gauge, with the driving techniques described above, added about 2 MPG.
The vacuum gauge plus wheel covers helped increase summer 2015 mileage to 38.5 MPG, while summer 2016 mileage was 38.6 MPG without the wheel covers. Drove 33,021 miles 2016-2018 at 35.00 MPG.

Last edited by JRMichler; 02-01-2017 at 09:40 AM..
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