2007 Yukon Poor Mileage

zwitter153

I have a 2007 Yukon 4WD I obtained six months ago. I now have 12K miles and in the last month I have noticed my gas mile plummit. I had been getting 19 miles to the gallon and it has dropped to less than 16. I drive 100 miles daily, all highway miles. My dealer is clueless. Anyone have a suggestion? The service engine light did come on once and went off by itself. Delaer says no codes were stored.

bluegender72

I feel your pain. I too bought my GMC Yukon 2007 six months ago and I am going through the same exact problems. First, my wife thought we were having a fuel leak as our mileage just went completely south. Second, the fuel gauge is never accurate and I understand that is because of the fuel management system, but nonetheless, it should closely reflect actual. Third, I started my car with the AC on and when I attempted to drive off, the car greatly hesitated and this horrific grind sound happened. My assistant has the exact same car and hers does the exact same thing. The dealer has no idea and is a complete waste of time. If you find out anything, let me know.

brewboy

You may wish to look at reprogramming the ECM with a programmer like the Diablo Sport Predator. Gains are minmal like 1-2 mpg but you gain 25HP at the wheels and increase in torque. This is the reason why the Escalade has the same engine and transmission but offeres 403HP as compared to our Denali 380HP.

zwitter153

I found a blurb on the GM website that said in order to increase mileage, turn the A/C off. You have to actually power the climate control system down by hitting the "1/0" button. Just turning off the compressor by hitting the little "snowflake" button will not do it. My milage came back up from 15.9 MPG to 21.2 MPG.

So, GM, What's the deal with the A/C? Is it the new freon that is loading down the engine so much? Defective A/C compressors?

obyone

6 mpg increase by turning the a/c off? Is this in city or highway driving. I'm assuming highway. That's unreal.

tidester

My milage came back up from 15.9 MPG to 21.2 MPG.

I'll be interested in seeing whether that persists or whether it is an aberration.

tidester, host
SUVs and Smart Shopper

zwitter153

I've been through one tank of gas now, all highway miles, and results are holding true. With the A/C on, I was filling the tank every 4 days. I was able to get 3 extra days without the A/C. With the A/C on, there is a noticeable drag on the engine, almost like towing a heavy trailer. Without the A/C the engine has all it's "pep" back. GM is still clueless as to why the engine is so labored by the A/C.

tidester

That's pretty amazing! Most tests that I have read^* about show very little difference in gas mileage between running with air conditioning and running without it. However, the "off" condition was done with the windows open which, of course, increases air drag on the vehicle. If you're running with air conditioning off and windows up then I could see some difference in gas mileage. Very interesting!

(^*) See e.g. Test #4 in our Fuel Economy article.

tidester, host
SUVs and Smart Shopper

dardson1

Everyone assumes fuel is a constant. Since ethanol, with many fewer btu's per gallon is the new additive (for whatever reason they need an additive), it makes a huge difference how much ethanol is in the blend. A full dose of ethanol in the blend can lower milage substancially. Unless you know what's in your fuel it's pretty darn hard to know the real milage.
Since fuel blends have moved from MTBE's (think that the name) to ethanol I've given up trying to keep up. My milage used to be fairly constant but these days it bounces around like crazy. It's the dang gasoline.