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Old 09-07-2011, 01:20 PM   #23 (permalink)
JRMichler
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Join Date: Feb 2011
Location: Phillips, WI
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Nameless - '06 GMC Canyon
90 day: 31.7 mpg (US)
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Yeah, I would also expect a small truck to get similar mileage to the Mercedes. Here's a few things that will kill mileage 30 or 40%:

1) Ignition timing retarded about 10 degrees. I don't know how this could happen with a computer controlled engine.

2) Fuel mixture always on full power enrichment. I don't know how this could happen with a computer controlled engine - maybe a WOT throttle switch failure?

3) A really bad burned exhaust valve. A compression test will diagnose this.

4) A seriously dragging brake. You would feel the heat radiating just standing near it.

5) (Maybe) Camshaft out of time - worn chain (does your truck have a timing chain or a timing belt?) or belt/chain jumped a tooth or two.

6) (Maybe) Worn lobe or two on the camshaft. This happened to me years ago. I know it will reduce power, I don't know if it kills gas mileage.

7) Something I haven't thought of.
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