Need Help, poor performance. 2004 Aveo

So I recently bought 2004 Aveo Manual 1.6L in Canada.

The car gave me 350km in a full tank (40L) on highway.

Then It gave me 280km in city with a full tank.
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I decided it needs maintenance, although the oil was relatively new, i still decided to change it.

I put Castrol Advanced Synthetic Oil in it. With a filter from FRAM and an air Filter from FRAM as well.

Used an Engine Flush liquid to clean up the engine

and put NGK platinum spark plugs in it.
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I filled up the tank with High octane 91 Gas, and It gave me 400km in a full tank in city,
I am still not satisfied with the performance as I drive a manual car a civic/corrolla/mazda3/acura gives better mileage than this car as I discussed with my friends who own these cars.

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Does someone have suggestions for me, i expect atleast 500km in a full tank, does anyone get than mileage? If you get it then how?

I'm not all that good with metric.. but you dont need to spend the extra money on the 91 octane gas.

A 50km difference between two tanks is not an average. A change in stop lights, driving speed, and a many factors can account for that loss.

Also, its the middle of winter, did your friends account for that? I generally experience a 10-15% (at least) loss in fuel economy based on winter blend/temperatures/etc. Also if your friends were talking about how far they get in a full tank compared to you, did you account for your tank size difference? Or are they talking numbers overall, or in the summer? Did you compare dirving styles, routes, etc? I am not generally surrounded by hypermilers to know if these conversations exist.

What kind of engine flush liquid did you use? an oil flush, fuel additive, coolant flush? If your running 91 octane with a fuel additive, the timing advance the computer would be using to accommodate that change as depending on what you have done you might be in the 94-100 octane range. You at least "compensated" for the 91 octane with platinum plugs.. sort of.

you need a little more info here to get credible advice imho.

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Originally Posted by Talha

So I recently bought 2004 Aveo Manual 1.6L in Canada.

The car gave me 350km in a full tank (40L) on highway.

Then It gave me 280km in city with a full tank.
____
I decided it needs maintenance, although the oil was relatively new, i still decided to change it.

I put Castrol Advanced Synthetic Oil in it. With a filter from FRAM and an air Filter from FRAM as well.

Used an Engine Flush liquid to clean up the engine

and put NGK platinum spark plugs in it.
_____________________

I filled up the tank with High octane 91 Gas, and It gave me 400km in a full tank in city,
I am still not satisfied with the performance as I drive a manual car a civic/corrolla/mazda3/acura gives better mileage than this car as I discussed with my friends who own these cars.

____________________

Does someone have suggestions for me, i expect atleast 500km in a full tank, does anyone get than mileage? If you get it then how?

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I do get that 500K per 40L in my 2005 manual (it's actually 32 MPG). Medium speed driving, but almost no stop-and-go or lights. Your "highway" mileage seems WAY too low. But what speeds are you usually doing? If you're travelling at very high speeds, plus lots of wind and/or hills, that might explain it a bit. Also, do you like to "wind it way up" all the time? That could be a big waste of fuel, depending on how much shifting you do. I shift at 2-3K, but never so early that the engine lugs.
"500K per tank" is ok for a rough calc, but in order to really be sure of what you're getting, you need to deal with exact numbers. Fill it up, and reset the ODO to zero. When nearly empty, fill again, record the mileage (Ks) and fuel usage, and also reset the ODO. Do this all the time, and then you have the exact KPL. And +1 to what PR said, skip the 91 and just use regular octane.

I shift In between 2-3K rpm, 2.5 to be exact, there is no rough driving what so ever, I have had cars before, the mileage is unbearable, the other cars I told have those statistics that are legit, everyone knows about it.
I just need advice on spark plugs/ air filter or something.
any great tip to boost up the mileage,

400 KM is very low for a 1.6L car that is being driven smoothly.

We have basically the same vehicle, and it also sounds like you drive similar to how I drive. So, based on the numbers you give, it seems that something may be wrong with yours. But the problem is, there are a large number of possibilities. First, how did the old plugs look? If you're not sure, there are pics available on the web of "good" used plugs, and the various flavors of "bad" plugs, along with possible reasons why they look that way. Next, how many KM on it, and how does the engine sound- any miss? Does the engine always stay strong, especially going up hills? Have you done a compression/ leak down test? Any OBD codes ever get set?
Some other things that come to mind are blocked emissions or exhaust, plugged/bad cat, bad O2 sensor. But one or more codes often show up when there's a problem in those areas. A couple of other things which are easy to check is a packed air filter/box (critters make a home there in 30 seconds), and also deposits in the throttle body. How about the wheels? Assuming the tires are full prressure, then perhaps a bad brake or wheel bearing. If you can find a place where you can drive for a few miles and then coast to a stop all without applying the brakes, none of the wheels should be hot.
Of course, there are a number of other possibilities as well, so just go through the list of every performance factor you can find, and eventually the problem will be identified and get fixed. Good luck with it!

One of the vacuum lines on my intake manifold cracked. It didn't set any codes or cause a miss of any kind, but was costing me about 10MPG. Cold weather can cause those to break. A friend happened to notice it, & when I fixed it, I got my mileage back. I can also attest to the O2 sensor problem. It should throw a code, but that bad sensor was costing me about 7MPG.

Yours does not seem to bad, i would still look into it but on my aveo the last few city tanks i got about 20 mpg but i also idle alot, i dont shut it off much when it hits 40 below, couple time last year i let it idle for a few days straight. Btw where in canada are you?

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Originally Posted by avguy

We have basically the same vehicle, and it also sounds like you drive similar to how I drive. So, based on the numbers you give, it seems that something may be wrong with yours. But the problem is, there are a large number of possibilities. First, how did the old plugs look? If you're not sure, there are pics available on the web of "good" used plugs, and the various flavors of "bad" plugs, along with possible reasons why they look that way. Next, how many KM on it, and how does the engine sound- any miss? Does the engine always stay strong, especially going up hills? Have you done a compression/ leak down test? Any OBD codes ever get set?
Some other things that come to mind are blocked emissions or exhaust, plugged/bad cat, bad O2 sensor. But one or more codes often show up when there's a problem in those areas. A couple of other things which are easy to check is a packed air filter/box (critters make a home there in 30 seconds), and also deposits in the throttle body. How about the wheels? Assuming the tires are full prressure, then perhaps a bad brake or wheel bearing. If you can find a place where you can drive for a few miles and then coast to a stop all without applying the brakes, none of the wheels should be hot.
Of course, there are a number of other possibilities as well, so just go through the list of every performance factor you can find, and eventually the problem will be identified and get fixed. Good luck with it!

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Thanks for this advice, I will also check my car as it gets terribly low mileage on a full at the moment.
OBD2 diagnostics are error free only plus 5 on the Long Term Fueling Trim.