Mechanical Issue? Large variations in instantanious mpg
I don't really know where to post this question because it isn't specifically related to EFIlive but rather the results I'm seeing in my vehicle and a possible mechanical issue preventing proper tuning. Mods: Please feel free to move this to a better section is necessary.
2003 GMC Sierra Denali_6.0_4L65E_4.10:1_AWD_QS_138,000miles
So I've been trying to get deeper into EFIlive tuning with Lean Cruise and DFCO and have been working on my GMC. The truck seems very solid and since I've completed some VE tuning it runs pretty smooth. The trucks is all stock with the exception of a Volant CAI + scoop and a set of Silverado E-fans. I just got back from a short trip and noticed something very odd as far as my MPG read-out on the DIC. At this point I'm getting between 15-18 mpg on flat ground at 65mph. On slight downhill grades it will go as far as 35mpg if DFCO hasn't engaged. On slight uphill grades it will go as low as 10mpg(worse of course on steeper grades). This uphill reading isn't always very predictable. There are times that I go up one hill and get Xmpg and then go up the next hill which seems to be steeper and get a better mpg reading.
What I noticed this weekend though was a little out there. . . The 150 mile drive has grades, both up and down. Most of the time the DIC reading followed an expected value but at one point on the way to our destination, I started up a grade (from a pretty flat road) which should have caused a reading of 10-12mpg but I was showing 16-18mpg.
On the way home today, I was showing 60mpg down hill with DFCO engaging, I hit the bottom of the grade and immediately started up the other side(again an expect 11 or 12mpg hill) and was showing 18-20mpg.
This occurred in varying severity over the rest of the return trip. The only perceivable difference when this occurs is that the trucks seems more smooth and responsive when it is reading the high mpg. Unfortunately I didn't have EFIlive hooked up either time I noticed the anomaly but I did observe that the fuel mixture didn't go outside the normal range.
I'm just wondering if this could be a mechanical issue. Perhaps a worn out timing set or torque converter/other transmission component. Or if there is an issue with the DIC read-out. (mostly I'm just hoping that it is a mechanical problem and if corrected I can get that kind of mileage regularly.)
Jesse
PS. this occurs with and without Lean Cruise or DFCO enabled.
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Originally Posted by andysc3
