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2004 EXT
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305 Posts
Discussion Starter · #1 ·
It's been awhile since my last post as i thought i might be selling my car....however now it seems that there is a slight problem (or at least i hope its slight). I've been experiencing terrible gas mileage (13.5 mpg) with about 165 miles per tank. I sea foamed intake & gas and it seemed to go up in gas mileage but it was only for a few miles. Furthermore its started hesitating on acceleration. I hope you guys have encountered this before....oh white pearl.:bigroll:
 

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06 CTS Sport/Luxury package
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9,858 Posts
Have your car scanned with a "live" scan tool. To see if they are any misfires. Some misfires you'll need a live scan for some dumb reason. This tool ain't your local autoparts store type, so you might have to pay a shop.

It may take a few minutes of scanning, or you might see a misfire right away. With mine I had 3 to 4 misfires on cylinder 2 with in 30 seconds.

KOT
 

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2006 CTS-V
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4,969 Posts
Also, replace your fuel filter. It cost like $10, takes less then 15 minutes to do with the right tools, and it will probably help the most. (its on passenger side, a bit behind the back door, underneath the car.
 

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NONE - was 2006 CTS. Now 2012 4LT Centennial GS Corvette
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388 Posts
Like already indicated, the first thing you need to do is find out what OBD codes are being thrown, if any. From your description I'd hazard an initial guess that you have a bad O2 sensor.

Check to make sure you don't have a leak somewhere in the intake between the throttle body and the air filter box.

Let us know what you find out after this.
 

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465 Posts
Max, I noticed you started having consecutive issues after the timing belt replacement, therefore, I would rule-out anything associated with the protocol of the job.

Also, new plugs, air filter and fuel filter will help with poor MPG, if timing belt is placed correctly.

Codes..?
 

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2006 CTS-V
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4,969 Posts
:yeah:

And check your trans cooler line. Those tend to fail very easily and you could be losing trans oil / possibly even mixing.
 

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2003 CTS
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2,337 Posts
my question would be, do you have a CEL on? if so, have the codes checked. The greatest mileage increase i have had was after changing out an O2 sensor that was bad. My mpg's got much better after that and cleared up the rough idle.
 

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2004 EXT
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305 Posts
Discussion Starter · #8 ·
so i should have my car scanned to look for misfires?

Where are these o2 sensors located?

i changed out my air and fuel filters. Could the fuel filter be clogged?

I had my timing belt stuff all done by "professionals" so hopefully they didnt f*ck anything up. Is there a way to figure this out?

And lastly how do i get that master air flow sensor off? Rather where can i find a tool (circle in the middle)?

thanks guys
 

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2003 CTS
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2,337 Posts
you have 4 o2 sensors. 2 before and 2 after the Cats. pretty simple to change
 
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