poor fuel mileage


Asked by Mar 01, 2008 at 02:11 PM about the 2005 Chevrolet Cavalier

Question type: Maintenance & Repair

I have a 2005 cavalier with a manual trans and the 2.2 ecotec engine. the first year and a half the car got almost 38 mpg. I drive all highway. The car is supposed to get 36mpg highway. I was happy. Now the best I can get out of it is 31.2mpg, averaged over many fillups. I drive exactly the same every week, same highway same speeds, same shiftpoints. What would cause this drop off? I put in a new set of plugs a few weeks ago at 65,000 miles. No improvement. I also replaced the fuel filter, air filter, and I do use fuel injector cleaner. The car has been back to the dealer several times, new fuel pump(took two trips to the dealer for them to believe it was really shutting off on the highway), some kind of very fast (3000rpm) idle problem.  Any idea where to look?

3 Answers


What type of plugs did you use? Anytime I put any other plug than AC Delco in a GM engine, the customer comes back, That is the only plug I recommend for GM engines. and it is always the customer who says to put the other plugs in. That could be one of your issues. A other thing is that cars lose some MPG as the cars get older and or more mileage on it. And what plug gap did the mechanic use? Alot just take the plug out of the pkg and put it in the car... If you still have issues, ask the mechanic to hook up his computer to your OBD port and take the car for a ride. His "scanner" will be able to see what you sensors are reading out while the car is driving. Best of luck.


Thanks for the response. I used Bosch platinum plugs, but the fuel mileage is exactly the same as the old plugs(and the car runs beautifully, as it did when it was new). I have no idea of what the spark plug gap was set at, what should it be? I own a 2001 Silverado with a 4.3 liter and 75,000 miles on it(it still has the original spark plugs), and it's fuel mileage actually improved as I put the miles on, not the other way around. I will ask the mechanic about the scanner, good idea, thank you.

change your ignition coil on these cars if you see a dramatic drop in mpg, along with wires and copper spark plugs. fyi always run full synthetic oil not blend full synthetic Castrol oil.

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