John Sampson

Hey everyone!

For about 4 months now i have been having very poor gas milage. I run through a full tank in about 200-250 miles. I do mostly highway driving which is very confusing. I do occasionally drive it hard of course, but even if i'm not driving it crazy all the time I still have poor fuel economy. Why would this be?

I used to get about 350-400 miles on a tank. Now i'm lucky if I get above 250.
I changed out spark plugs without much improvement
My car is a 2002 Boxster 2.7L with 120k miles

Any suggestions would be appreciated!

I usually shift at around 3000 RPM as I am accelerating, but on the highway ill go into 5th gear.

Weazer

Check for any codes, may be something pending. Maybe tired oxygen sensors? May not throw a code yet still cause a rich condition and consequent poor performance/gas mileage, plus the additional fueling washes down your cylinder walls causing premature wear. May want to pull your plugs and check the color, tips should be whitish tan in color, if they are sooty they are gas fouling. I just recently changed out all 4 oxygen sensors on my 996 although I wasn't getting any codes, and the engine seems to run much smoother and throttle response seems snappier. Also, make sure your air filter element is clean.

Byprodriver

Run some fuel injecter cleaner in the tank, that should help, or if you want it as good as can be, remove the injectors & have them cleaned by a specialist shop, you may have 1 leaking.