# mpG



## steve20 (Jan 12, 2005)

I just got 225 miles out of a 16 gallons of premium(93) in the city. Can someone help me out and calculate what the mpG comes out to? Thanks!


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## bluemax95 (Sep 25, 2004)

225 miles / 16 gal = 14.0625 miles per gal


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## steve20 (Jan 12, 2005)

bluemax95 said:


> 225 miles / 16 gal = 14.0625 miles per gal


 Thant's what i thought, but when saw the figure couldn't believe it, thought i was doing something wrong. So how can i improve the gas milege? I have 2000 I 30...


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## am3rican (Feb 26, 2005)

other then being 225 miles of city driving, give us some more details (i.e. was there a lot of idling? did you floor it at every light? or did you drive like a normal person should?) without more details, we cant diagnose the problem.


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## Jeff (Oct 17, 2002)

It 'should' be about 100 more miles on the tank than 225...

Answer Am3rican's questions and then tell us if you have any codes or when your last tune-up was.
You could have a bad knock sensor.


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## steve20 (Jan 12, 2005)

am3rican said:


> other then being 225 miles of city driving, give us some more details (i.e. was there a lot of idling? did you floor it at every light? or did you drive like a normal person should?) without more details, we cant diagnose the problem.


maybe a few minutes of ideling, never floored the pedal eather. Did use AC a few times... I did not do a tuneup since i got the car 3 weeks ago. 

Thanks for the input guys!


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## Jeff (Oct 17, 2002)

Usually when the knock sensor goes out you will lose big on mpg. If you have any mechanical knowledge then check the spark plugs for age. It could be something as simple as dirty filter or clogged fuel filter.


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## steve20 (Jan 12, 2005)

MrEous said:


> Usually when the knock sensor goes out you will lose big on mpg. If you have any mechanical knowledge then check the spark plugs for age. It could be something as simple as dirty filter or clogged fuel filter.



Thanks for the tips. What's "knock sensor" ?


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## Jeff (Oct 17, 2002)

Knock sensor is an engine sensor that detects knock. When it does detect it, it will retard the timing and dump more fuel to compensate...causing poor gas mileage.


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## cardana24 (Oct 15, 2003)

sounds like you have a lead foot with a huge fuel leak. Or someone is coming by and sticking a siphon hose in your tank at night. My car is supercharged and even when I boost a lot I still get better gas mileage than that.


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## brianw (Feb 25, 2004)

Failing O2 sensors can grossly affect fuel economy. Try those first, all three of 'em.

In a supercharged `97 autotragic I was still getting 16-20mpg in the city, average of 18mpg with 50/50 driving mostly in traffic and hitting boost all the time on onramps... 14mpg is pretty low unless you're doing all sub-10-mile drives on city streets, in which case 14mpg is unlikely but possible.


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## steve20 (Jan 12, 2005)

brianw said:


> Failing O2 sensors can grossly affect fuel economy. Try those first, all three of 'em.
> 
> In a supercharged `97 autotragic I was still getting 16-20mpg in the city, average of 18mpg with 50/50 driving mostly in traffic and hitting boost all the time on onramps... 14mpg is pretty low unless you're doing all sub-10-mile drives on city streets, in which case 14mpg is unlikely but possible.


If o2 sensor was bad, wouldnt' computer detect it + the light would be on...

Well, i do leave in New York. So 80% are city ~10 mile drives + parking+ ac ect. I'm going for oil change next Saturday, and will talk to the mechanic about this. My friend with Jeep GC gets 10 in city...


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## brianw (Feb 25, 2004)

No. o2 sensors usually _gradually degrade_, which means that short of the sensor coming unplugged or completely corroded, the computer will _not_ detect a failure.

IIRC Q45Tech or someone else on this forum said to typically replace o2 sensors every 70k-80k miles or so if you are worried about them degrading.


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## steve20 (Jan 12, 2005)

brianw said:


> No. o2 sensors usually _gradually degrade_, which means that short of the sensor coming unplugged or completely corroded, the computer will _not_ detect a failure.
> 
> IIRC Q45Tech or someone else on this forum said to typically replace o2 sensors every 70k-80k miles or so if you are worried about them degrading.



Thanks! I'll check the filters, plugs and knock sensor. If that doesn't work then i'll definetly look in to getting a new O2... I have 110K on it


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## Jeff (Oct 17, 2002)

...why replace a sensor if you aren't getting a code? The ecu would come on for o2 sensors whether they are completely not working or even if there are voltage irregularities.

Now the Knock Sensor could be a ghost code and never show up with the check engine light but not an o2 sensor.


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