MPG decreasing-HELP!! From a newbie

[2007gmcyukon]

Hi,

My name is Amy and I have a 2007 GMC Yukon. It's the SLT model, 5.3 L, 2WD and has just over 75,000 miles.

I recently noticed my MPG were decreasing. In a matter of about 2 weeks, they have gone down from about 16 to 12. I've changed my air filter and checked the air in my tires. Oil is good and not in need of being changed.

I'm sure it could be a lot of different things, and I;m sure it's impossible to diagnose the problem purely by using this site. But I'm trying to learn about my car. I thought I'd join this forum to hopefully gain some insight. I'm sure I need to take it in, but I don't have a good mechanic and I'd like to understand what I'm dealing with instead of take someone's word for it.

Any insights or advice would be greatly appreciated. Thanks for reading and thanks for your time.

 

[ezdaar]

By some mass air flow cleaner, its a spray can. clean your MAF.

O2 Sensors, replace the primary (front) O2 on left and right side.
If you can change a air filter you can change your O2's. Buy the correct socket for a O2sensor and get busy girl.

Could also pour in a bottle or two of some injector cleaner. I run 2 bottles through at a 1/4 tank of gass, every time I change my oil.
Might aswell change Fuel filter while your at it..

GL.

 

[emann_01]

getting the throttle body and intake manifold cleaned could help...this is a packaged service that GM dealerships offer

 

[2007gmcyukon]

Thank you thank you thank you for your help! I'll look into this...It's kind of fun, I always wanted to learn about cars, but never really knew where to start. This site is great, and it's nice you you all to be so helpful.

 

[bauer4567]

Had the info under your username said "Name: (insert any male name) and Location: (insert anywhere except So Cal)" instead of "Amy from Socal" The answers may have been a tiny bit more condescending

But all the above are good places to start!

 

[Zed 71]

Hi,

My name is Amy and I have a 2007 GMC Yukon. It's the SLT model, 5.3 L, 2WD and has just over 75,000 miles.

I recently noticed my MPG were decreasing. In a matter of about 2 weeks, they have gone down from about 16 to 12. I've changed my air filter and checked the air in my tires. Oil is good and not in need of being changed.

That's a drastic change in mpgs. Just a few Qs.
- How are you calculating mpgs? Over what period is this being calculated?
- Weather conditions same or drastically changed?
- Same tank of gas?
- Is this the same route or driving habits?
- Any changes like brand/octane of gas, additional wieght in the truck, carrier on top, etc.?
- Since you have 75k miles, has the 60k service been done? Was the same air filter used?

 

[2007gmcyukon]

That's a drastic change in mpgs. Just a few Qs.
- How are you calculating mpgs? Over what period is this being calculated?
- Weather conditions same or drastically changed?
- Same tank of gas?
- Is this the same route or driving habits?
- Any changes like brand/octane of gas, additional wieght in the truck, carrier on top, etc.?
- Since you have 75k miles, has the 60k service been done? Was the same air filter used?

Hi,

I thought is was a pretty drastic change. It's always been about 16, and it started decreasing maybe 2-3 weeks ago. Not it is at 12, and this is according to the car, what it says on the driver information center.
No significant changes in weather and no driving route, habit or gas changes.
I don't think I did the 60K service, maybe I should start there. That seems like a good idea and I feel a little stupid for not doing that. Ooops. Is that something I can schedule with a regular mechanic or does it have to be done at the dealership? Thanks for your help.

 

[Zed 71]

First try and calculate the mpgs using the actual miles and gallons from the gas dispenser. Let's see what you get. Are you reading the instantaneous or average mpgs on DIC? Check odometer by confirming route with GPS or Google Maps. Just trying to confirm the most obvious things are working correctly.

Now it's dropping from 16 to 12 mpgs... Geez, with something that drastic you would probably notice a change in vehicle dynamics (assuming everything else is the same).

As far as 60k service go to the cheapest place you trust (not one of those quick lube places). Call around. If you are up to the task, most of it can be done at home.

 

[2007tahoe]

Did you ever get your mpg back up? My truck usually averages 13.6 for the last year. All of a sudden it droped to 11 when it got really hot out side in a matter of weeks. I have changed to 93 octane from 89 and tried a few different gas stations with no change. I have already did an engine clean about 10,000 miles ago (intake drip, throttle body clean, and injector clean). I never get on it and drive like grandpa. It has 66,000 miles on it. It does not have to do with now added alcohol in the fuel because I owned this truck in Cali and they have had alcohol in fuel for years. The only thing that is different is I think I put 10-30 synthetic in last oil change instead of 5-30. I donot think that would drop mpg down by 2. I was going to get a black bear eco tune and was hoping for 14.5 to 15 mpg average. But now I am going backwards for no given reason. I will sell the truck before I spend 800 on a tune and intake to get 13mpg that I was getting before. It is a 2007 2wd 5.3 nonflex fuel. thanks for anyhelp.

 

[Sheriff]

I think what you are dealing with here is different driving styles. The previous owner(s) might have done 85% highway driving. And if you're now doing 85% city driving, the drop is easily explained. The computer does not reset your mpg with each fueling. It keeps a runing total over the life of the vehicle and how many gallons it has used in it's lifetime. If it ever drops below 10 mpg, then you have reason to worry.

My Z71 has dropped to 11.4 mpg, 98% city driving. But it's still better than the 8 mpg I am getting on my Ford Excursion.