I have a 2002 Cavalier 2.2 with 125,000 miles, and in the summer, I was getting close to 40 mpg but now, barely 22 mpg and 95% is highway driving. What gives? Oil changed 200 miles ago, used injector cleaning stuff in the gas, 4 tanks ago, and a brand new Spectre Short Ram Intake. Engine light is on for a small EVAP leak, but the light was on in the summer also so I doubt that's it. I understand winter knocks a few mpg off but not this much. I don't drive like a maniac but I don't drive like a old lady either. I travel around 320 miles a week and considering a Saturn for fuel economy, even tho I love this car

Do you let it idle to warm up the car now? Also the new intake may affect your mpg as well.

Naw, I always just start and then drive right away. And I kinda figured, but wouldn't the freed up air flow help the economy?

Could it be that the oxygen sensors going bad?

Could be the upstream O2 sensor. I replaced mine around 100k miles because mine was getting a little slow. I'd recommend you stick with AC Delco if your shooting for the best fuel economy.

And the intake may help fuel economy but that's only likely if you keep your foot out of it (my fuel economy went to crap when I put a aftermarket muffler because I loved to hear the sound).

Winter is a killer. Winter blend fuel doesn't get you the mileage it should. When it's cold the car dumps fuel to keep the mixture stoichiometric, especially when the motor is still warming up. I lost a solid 8 mpg highway this winter.

Still, it can't hurt to change that upstream o2 sensor out for a new ac Delco piece. Just be ready to pay.



"In Oldskool we trust"

I second yellowcav, every year I get customers come in saying in the winter there gas mileage suddenly isn't what it used to be. I blame winter gas and people tend to let there cars warm up 5-15 minutes before driving them anywhere. the engine also takes longer to warm up which in turn dumps more fuel into the engine.

Thanks for the replies guys. I agree that winter is a killer but right now, I'm averaging 19 MPG highway right now and easy on the pedal, I know winter winter knocks a few mpg off but 10-15 mpg off? And I just might replace the O2 sensors in the spring when I'm planning to do a lot of things to my car. Tomorrow I'm taking it to my school's auto shop class to smoke test it. My auto shop teacher thanks there's a major vacuum leak somewhere but I'll keep you guys updated!

Does it idle properly? If it does there's no vacuum leak. Also, don't waste your money on a downstream(after cat) o2 sensor unless it's throwing a check engine light.

I didn't even read that the check engine light is on the first time. That can kill mileage too.



"In Oldskool we trust"

It idles perfectly, always stays at 900 rpm, never jumpy and so what. And the light has been on since I got the car, 7,000 miles ago, and
It's for the EVAP. Should had it checked up a long time ago but didn't think of it until my mileage is really dropping.

Yeah that's definitely your problem. If the evap isn't right the car won't run right and will dump fuel. Fix that and enjoy your improved economy. You try the gas cap?



"In Oldskool we trust"

Really? Tomorrow is the final time I deal with that light, and the crappy economy and hopefully fixes it. And yes, new cap around a month ago, new canister purge valve around a week ago, along with a new hose for the canister to the valve. Still throwing the EVAP code.

Gonna have to smoke it with a smoke machine to find the leak. But yeah that's definitely the problem.



"In Oldskool we trust"

My auto shop class has one I could use. Not really worried about repair costs because I do all the work myself using the school's tools and such. And it's 600 rpm, not 900, my bad haha. But thanks for the help, you cleared everything up! Just never knew EVAP could murder my mileage

Update: used the smoke machine to locate the leak, and it was pouring out of the purge valve, the one I JUST replaced, but the thing is, the entire EVAP system in the back won't listen to the OBD scanner as we commanded it to open and close. It just said it was closed, yet smoke was still pouring out. We tested the other valve also and that wouldn't do nothing. Is it an electrical problem? The scanner can control everything on the car but the EVAP system, which I'm finding pretty weird....I just have a feeling it's an wiring issue somewhere.

You should have constant power at the pink wire on the plug and the ground should switch when you command it on the dark green wire with the white tracer.

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Thanks for the diagram. But today I pinpointed the problem, I unhooked the canister hose and gas was dripping out, so the canister (IMO) was clogged up forcing the purge valve to stay open, because the vapors don't have anywhere to go. Luckily my teacher had a spare one in his parts shed and I hooked that one up, and to my surprise, the purge valve finally closed when I commanded it to on the scanner, and I confirmed the smoke machine was still running. So I cleared the light, hopefully it doesn't come on now. Also I noticed on the canister that around the cap or cover or whatever, that it was all wet and reeked of gas. Sandblasted the bracket and now it's done! Just now I have an grinding vibration at exactly between 15-20 mph..