CRAPPY highway mileage from my '07 Vibe!

[bsd70]

Good day...I need help with something, I figured you Vibe Masters would have an idea. My '07 Vibe (with about 137,000 KM on it) is getting much worse mileage on the highway (about 17 mpg) than in the city (about 27 mpg). I've had a tune-up, a fuel system cleaning, a wheel alignment, a new engine air filter, a mass airflow sensor cleaning - still no improvement. And the tires are fine. No check engine light has come on. Three mechanics I've spoken to are stumped . Do you fine folks have any idea what the problem might be?

[Baltovibe]

Catalytic Converter failing?

[vibrologist]

Is it shifting into overdrive? What is the tachometer saying at 70 mph?

[tpollauf]

Welcome to GenVibe .... although I wish it were on better terms! You definitely got something weird going on there. Not to rub anything in BUT here's a snapshot of my 2012 Chevy express 2500 (8000lb work van w/5.3l V-8 engine) getting an impressive 20.7 mpg on the Ohio turnpike the other day (had a good tail wind!). Too many factors to look into. Bad fuel, ECU acting up, tranny slipping (check RPM's), etc. Let us know what you find and post pics of your Vibe so we all know what you're driving!

[jolt]

Did anyone try pulling any trouble codes from ECU? Does the check engine light work? Did you do a gas mileage check the old fashion way and compare that to what the dash is saying? Automatic or manual transmission? Have any of the three mechanic worked on the car?

[ehoff121]

My '07 Vibe (with about 137,000 KM on it) is getting much worse mileage on the highway (about 17 mpg) than in the city (about 27 mpg). I've had a tune-up, a fuel system cleaning, a wheel alignment, a new engine air filter, a mass airflow sensor cleaning - still no improvement. And the tires are fine. No check engine light has come on. Three mechanics I've spoken to are stumped . Do you fine folks have any idea what the problem might be?

Welcome to genvibe!

Assuming you have a base FWD, the estimated US MPG is 30 city/36 hwy. You gave the odometer in km, but the fuel economy in mpg.

How are you measuring fuel economy? There are a ton of variables that can affect it. What is your cruising speed during highway driving? Anything over 70 mph (112 kph) is going to impact mileage. How aggressive are you when you drive? Do you "floor it" getting on to the expressway? Is the A/C on? Windows down? Tires properly inflated according to door sticker? No extra weight in the car, e.g., sandbags, "stuff", significant other, etc.? Is the road flat or hilly?

Not sure what a "tune-up" is since there's not much to tune up besides cleaning the throttle body, IACV, MAF, or changing spark plugs.

[Derf]

How long have you had the problem, 2, 3, 5 fillups? Using the same station for fuel? I had seen were fuel economy slipped because of fuel blending, more ethanol, goofy mixup in winter to summer blend. I agree on the transmission, if it is automatic, their could be drag, shifting, or fluid issues. Their had been one post about intake manifold gasket issue causing poor fuel economy, but that issue usually creates a check engine/trouble light.

The fuel line or tank could also be the issue. Had one vehicle that you could smell a faint oder of gas, but could never find a leak. Turned out that it leaked only when the fuel pump was running, it had a fine pinhole stream of gas out the line, engine off, the pinhole quit and their was no dripping.