Thread: Gas Mileage

I be done almost everything I can to TRY and improve my gas mileage. I replaced the resonator with a straight pipe since it had a hole in it, I did a tune up, I sea foamed the car, and yesterday I changed the ecg valve or something like that. And after all that its still showing up 10-13 MPG...wtf.

I understand a used cars needs repairs, and I am willing to put money into it as long as it improves, not sets me back. Its really frustrating, and the valve is now making some weird noise D:

I DID have a Check Engine Light, but that was the valve, which I replaced. How would I know if its a shot o2 sensor or vacuum leak?

Not sure if it's the exhaust, but there's a lot of loud and weird noises D:

I changed the fuel filter, and the pump IS making noise. Havent really looked into the lines for leaks, neither the o2 sensor. How would I check if the cat is clogged? I rarely ever heavy foot it unless I need to, and there's no way I heavy footing it as much as where it drops down THAT much. I go into the car this morning to warm it up. What started at 13 mpg, ended at 3.1 mpg by the time the car was done warming up...D:

Thanks for the suggestion, but I've reset it almost every time I would pump gas.

The DIC isnt always correct even resting it, my Silverado normally says 13.8-14.5 and I regularly get 16-18, not sure with the Prix, havent even had it a week so we have yet to run a full tank through it

Originally Posted by akaMatt

have u actually tried dividing the miles driven by the gallons bought?? i never reset mine, and its actually pretty close... i get 21.x in mixed driving/commuting...

That, I havent done no. I'll have to try doing that the next time I fill up.

Originally Posted by BlackSun

I go into the car this morning to warm it up. What started at 13 mpg, ended at 3.1 mpg by the time the car was done warming up...D:

Of course your MPG isn't good your sitting still. Also check your tire pressure.

What he said. How far had you driven it to get the 13 mpg? These don't have an 'actual' mpg, it is averaged. If you filled up and then went home and parked it and ended up there with 13 then of course you only had 3 after sitting there warming up. You are using gas and going nowhere, so your mpg's while warming up are zero. It only needs 10-15 seconds of warming up on a cold day before you can drive it (carefully until it reaches operating temp).

As mentioned, you need to check how many gallons it took you to drive the miles you got out of that tank. If you do a lot of excess idling and warming up and only drive around town you will never get good mileage. My DIC usually shows about 30, but I drive 99% of the time on the highway, and even then I find it to be about 5-10% optimistic.

Originally Posted by 40th GP

What he said. How far had you driven it to get the 13 mpg? These don't have an 'actual' mpg, it is averaged. If you filled up and then went home and parked it and ended up there with 13 then of course you only had 3 after sitting there warming up. You are using gas and going nowhere, so your mpg's while warming up are zero. It only needs 10-15 seconds of warming up on a cold day before you can drive it (carefully until it reaches operating temp).

As mentioned, you need to check how many gallons it took you to drive the miles you got out of that tank. If you do a lot of excess idling and warming up and only drive around town you will never get good mileage. My DIC usually shows about 30, but I drive 99% of the time on the highway, and even then I find it to be about 5-10% optimistic.

That honestly really helps, I always give the car 5-10 mins of warming up only because literally EVERYONE says you have to wait until the temperature hits like 180 before driving -__-

I changed out the plugs and wires about a month ago so I doubt that could be the problem.

Other than that, I'll just have to calculate it myself and see what I get. Thanks a lot to every one of you for the help, I really appreciate it.

Originally Posted by Remnant King

I always give the car 5-10 mins of warming up only because literally EVERYONE says you have to wait until the temperature hits like 180 before driving -__-

That's ideal, but I bet 95% of people don't do that. Typically, unless it's really cold, I give my car about 2-3 minutes, then just take it easy until it warms up to where I can see it's 160 or better.

Originally Posted by Remnant King

That honestly really helps, I always give the car 5-10 mins of warming up only because literally EVERYONE says you have to wait until the temperature hits like 180 before driving.

That's your problem. If you are doing that and you drive mostly around town you will probably never get more than about 15 mpg at best. You only need 10-15 seconds of warming up to get fluids cirulated and oil up to the top of the engine, then just drive it easy until fully warmed up.

Bringing this thread back up because I finally got the chance to calculate it the way it's supposed to be. I filled up the car with 11.2 gallons, and I drove 168 miles with it. After the calculations, it gives me exactly 15 miles to the gallon, which is even LOWER than what the DIC is showing :\

It's getting a little frustrating to be honest haha.

Only thing I can think of to do would be replacing the O2 sensors, cleaning/replacing the catalytic converter, or a vaccum leak which would throw a code right?

Just a recap, this is what I have done to the car already:
Replaced Spark Plugs and Wires
Replaced a valve (ECG or something)
Replaced the shot Resonator with a straight pipe
Seafoamed the car
Used Injector Cleaner
Replaced Fuel Filter

I am usually just driving from my house to college, or around town.

I only go on the highway either once or twice a week.