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2006 Hummer H3 very poor mileage all of the sudden


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2006 hummer h3, 5 cyl. About 125k miles.

Used to get at least 15 mpg, now it's more like 10 mpg.

I changed the spark plugs, air filter, ignition coil.

Ran some injector cleaner.

Still no luck.

No engine light on/no code. My scanner is an actron cp9580 but beside reading and after repair removing code that's all I know to do with it.

4 Answers

The manufacturer's web site says it records live data - including things like a too rich fuel mixture.

Check out their how-to videos - bottom of page, under the price


To be honest I have no clue how to use the scanner beside reading and erasing codes. I'm going to post pics of what the scanner shows.


Start with checking the fuel trim data.


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Couldn't figure out how to add is a slideshow of what the scanner shows 

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I put 10 seconds between each slide so it can be read..