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2010 Pontiac G6 GT 3.5L Flex Fuel
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Hey y'all, I got a 2010 Pontiac G6 GT 3.5L. All of a sudden I noticed a significant drop in gas mileage. I used to average around 22 or 23 MPG. Now I average around 16 MPG and having to fill up a lot more. I've changed the spark plugs, ran a fuel system cleaner through, also made sure my tires are set at the correct psi. Any thoughts? Thanks!
 

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Hey y'all, I got a 2010 Pontiac G6 GT 3.5L. All of a sudden I noticed a significant drop in gas mileage. I used to average around 22 or 23 MPG. Now I average around 16 MPG and having to fill up a lot more. I've changed the spark plugs, ran a fuel system cleaner through, also made sure my tires are set at the correct psi. Any thoughts? Thanks!
I assume you have checked for gasoline leaks, checked the fuel filter and fuel pump? Have you noticed an increase in the exhaust, any backfires, or leaks in the exhaust system? I have 3.9L and get around 16mph around town and 23mph HW. Not great, but consistent - so I think something on your car has failed. As someone else said, check to see what error codes you are getting.

Finally, take it to a reputable dealer and ask them to troubleshoot :)
 

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2007 G6 GT conv
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I had a similar issue with my 3.9L. Turned out to be the air flow sensor unit . It was not operating properly and causing the computer to issue more fuel to compensate for the "supposed" low air-to-fuel mixture. Hence more fuel usage and low mileage numbers. Got that replaced and its' working reasonably fine. Good luck.
 
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