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Discussion Starter · #1 ·
Hi guys,

so i would like your opinion on something, i have a Cobalt LT 2.2L stock, only thing i changed was the muffler to an aftermarket one, because the other one fell of the brackets, cause the braket felt off. Lately ive been getting about 21,38 mpg to 19Mpg or 11.7L to 12L /100km on my car and so i can't get much more than 186 miles a tank (300km). That is on steel wheels an i get 23,52mpg (10.7km/100km) on aluminium wheels and also chek engine light appeared too and it's the P0456 Small leak, and i tought to my self if it's a small leak it would not be taking that much gas, so im asking you your opinions on what can cause that much of a big consomation.

Cobalt LT 2.2L 2D 2009
160 000 km (99419,3908 miles)
Manual Transmission
 

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I’m certain you have checked what issues might cause evap system error code P0456.

One issue that might noticeably affect your mileage is a leaky fuel tank sending unit / gasket.
There have been other known issues with cracked, leaking hoses, and a bad fuel cap.

while it’s quite difficult to check since it’s on the top of the fuel tank, you might be able to fish some toilet paper on a wire ( coat hangar) and swab around the top of your fuel tank. That or get a fiber optic camera and perform a visual inspection with a full tank looking for wet fuel spots. Another is to get a service shop to vacuum check your system.

it makes a difference if your car is a California emissions car or a federal emissions car. Different components.
And on the highway, you should be getting a good +30mpg…. I normally get between 33 and 37 with an average speed of 65-75mph up and down I-35 from Dallas to OKC to Tulsa and back and from Dallas to Shreveport and back on I-20
Using an 08LS BC with an L61 2.2L 5 speed and cruise most of the time.
Now to replace any of the fuel tank top components, do it with an empty fuel tank! Having gasoline sloshing around with the filler hose disconnected is no fun.

PS please check your decimal points…,it hurts too much to guess if you were getting 2138 mpg or if your Cobalt has 994 million miles or is that .
21-38mpg. Either is fine on mileage, 21mpg in stop & go city driving is not out of line and 38mpg is quite good on the highway and shows good highway driving skills. Btw just having a little fun with ya
enjoy
 

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Remember you have multiple lines and fittings into and out of your fuel tank
Fuel source…,to the engine
Fuel return ….from the engine
Vapor line to vapor canister purge….there are others

you might also look for rusted fuel line or a fuel line rubbed by a clamp developing a hole.
 

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Discussion Starter · #4 ·
Remember you have multiple lines and fittings into and out of your fuel tank
Fuel source…,to the engine
Fuel return ….from the engine
Vapor line to vapor canister purge….there are others

you might also look for rusted fuel line or a fuel line rubbed by a clamp developing a hole.
Alright i will be trying what you said, or i will send it to a mechanic. Thank you for your reply and sorry for the decimal here in canada since we're using km and L, i used a online converter and thought to myself these numbers don't make any sense to me 😂 no offense taken here.

Thank you.
 

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the evap and fuel line rust out just in front of the drivers side rear wheel. They are wrapped in a heat protective thing near the muffler. I had that code and when I took that wrap off the fuel line was so rusted it started leaking. Evap line was also rusted thru. If fuel line is bad you can buy a flexible plastic/vinyl ? replacement fuel line, goes whole length from filter area to engine. Like said above, when was the spark plugs, fuel filter and air filter changed, all will effect fuel milage, especially air filter.
 
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