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wmjinman · 12-13-2012, 01:31 AM

The other day, I jacked up the rear wheels on the Jimmy and gave it a shot. Interestingly, cruise control wouldn't work. Maybe it has some sort of "smart" programming that knows the front wheels aren't turning - or that there's no load on the engine. (the ABS light came on eventually, so that's why I'm wondering if it "knew" the front wheels weren't turning).

So, very carefully with the foot throttle, I kept it at 50 mph for 2 minutes and got an average "trip" MPG on the ScanGauge of 48.2. I also noted it was at 1550 RPM.

I then did one at 2000 RPM (which the BSFC chart showed to be more efficient), and that one worked out to 65 mph and with one minute on the ScanGauge got 49.5 MPG.

Then I tried it in 3rd gear at 2800 RPM, the best RPM for BSFC. (I was afraid to spin the wheels that fast in overdrive, although I didn't notice anything (vibrations) to make me worried it was trying to hop off the jackstands). Of course, in 3rd gear, I was covering less "miles", so it was only 34.9 MPG.

I noticed the temperature was climbing during all of this, so I went back to 50 mph in top gear and did another one. This time, it came out at 52.8 MPG after running the "trip" on the ScanGauge for 1 minute.

About this time, the neighbor came over & asked if I was having "car trouble", so I figured I'd better quit this "horsing around" before someone else got curious/concerned.

After that, I went ahead and changed my oil & put Mobil-1 synthetic, 5-20 in it. Up until this time, I'd always ran Pennsoil 10-30, or maybe 5-30. So when I get the chance, I'll have to jack it up again and try the experiment again & see if there are any changes.

For the sake of safety, in case it "hopped off" the jackstands at 50 or 60 mph, I was parallel parked on the street in front of my driveway, facing down the street with no cars in front of me for several houses.... and I was IN the driver's seat while it was in gear. So I told myself if any mishap occurred, I could probably hit the brakes & stop it before anything "bad" happened.

12-13-2012, 01:31 AM	#24 (permalink)
wmjinman Master EcoModder Join Date: Oct 2012 Location: Carson City, Nevada Posts: 612 Jimmy - '00 GMC Jimmy SLT 90 day: 21.18 mpg (US) The White Gnat - '99 Suzuki Swift Team Suzuki 90 day: 51.87 mpg (US) Thanks: 240 Thanked 114 Times in 90 Posts	The other day, I jacked up the rear wheels on the Jimmy and gave it a shot. Interestingly, cruise control wouldn't work. Maybe it has some sort of "smart" programming that knows the front wheels aren't turning - or that there's no load on the engine. (the ABS light came on eventually, so that's why I'm wondering if it "knew" the front wheels weren't turning). So, very carefully with the foot throttle, I kept it at 50 mph for 2 minutes and got an average "trip" MPG on the ScanGauge of 48.2. I also noted it was at 1550 RPM. I then did one at 2000 RPM (which the BSFC chart showed to be more efficient), and that one worked out to 65 mph and with one minute on the ScanGauge got 49.5 MPG. Then I tried it in 3rd gear at 2800 RPM, the best RPM for BSFC. (I was afraid to spin the wheels that fast in overdrive, although I didn't notice anything (vibrations) to make me worried it was trying to hop off the jackstands). Of course, in 3rd gear, I was covering less "miles", so it was only 34.9 MPG. I noticed the temperature was climbing during all of this, so I went back to 50 mph in top gear and did another one. This time, it came out at 52.8 MPG after running the "trip" on the ScanGauge for 1 minute. About this time, the neighbor came over & asked if I was having "car trouble", so I figured I'd better quit this "horsing around" before someone else got curious/concerned. After that, I went ahead and changed my oil & put Mobil-1 synthetic, 5-20 in it. Up until this time, I'd always ran Pennsoil 10-30, or maybe 5-30. So when I get the chance, I'll have to jack it up again and try the experiment again & see if there are any changes. For the sake of safety, in case it "hopped off" the jackstands at 50 or 60 mph, I was parallel parked on the street in front of my driveway, facing down the street with no cars in front of me for several houses.... and I was IN the driver's seat while it was in gear. So I told myself if any mishap occurred, I could probably hit the brakes & stop it before anything "bad" happened.