Power vs. Fuel Economy Question

Nevada_TDI

Top Post Dawg
Joined
Aug 17, 2008
Location
Reno, sort of...
TDI
2001 Jetta TDI
I have been looking at other posts/forums and have not been able to find an answer... Here is kind of the short version: how and or why would reducing my static IP timing and increasing my Adaptation timing cause a huge fuel economy increase?

Before: IP set at top of graph and Adaptation at 2-2.5; 35 MPG absolute best on freeway at 65-70 MPH.
After: IP set at mid 50's and Adaptation set to 5.5; 46 MPG driving as fast as was surrounding traffic. Every possible speed between 55 and 85 driven on California freeways.
History: We traveled from Reno-ish at 4600' elev to Cambria, California at sea level and back. On an 820 mile round trip, I filled to top before leaving (with winterized diesel) drove 500 miles and added 5 gallons of non-winterized diesel, drove 320 more miles and filled to the top once again with non-winterized diesel; I maintained a 2% Bio-D from start to finish.

What gives? I realize winterized diesel has less energy but certainly not 25% and I was not driving moderately for the majority of the trip.
A couple of things noticed: I did not have the same power at WOT above 3500 RPM, but the power band seems to come in quite strong at 2500 RPM or so--which did not happen before--, and there is more "clatter" when the engine is at idle, and significantly more at WOT.

According to everything I have read, my current timing settings will not cause any harm in the long or short term, but can reducing the total timing cause such a huge increase in fuel economy? Am I missing something, and if so will those knowledgeable please respond to help clarify this question for me? Sorry for the long post.
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
Maybe the previous timing was very sub-optimal for winterized fuel. The fuel itself may be responsible for ~10% of the discrepancy.
 
Top