Poor gas Mileage

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ChunHimself

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Even after I put some 285/75/16 tires on my 2000 Z71 I swear I was getting 15-16 mpg. That had to be 7+ years ago. Recently I've been getting 12 mpg even after I changed the fuel filter, spark plugs & wires, and air filter. No SES light, adaptation values: short term B1=1.56, short term B2=.78, long term B1=3.91, long term B2=3.12. I’m running Costco 87 octane fuel.


Any ideas? Trolls welcome since I’m new to the forum!
 

PAChevy

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Even after I put some 285/75/16 tires on my 2000 Z71 I swear I was getting 15-16 mpg. That had to be 7+ years ago. Recently I've been getting 12 mpg even after I changed the fuel filter, spark plugs & wires, and air filter. No SES light, adaptation values: short term B1=1.56, short term B2=.78, long term B1=3.91, long term B2=3.12. I’m running Costco 87 octane fuel.


Any ideas? Trolls welcome since I’m new to the forum!
There are a number of conditions that can contribute to lower fuel mileage. Have you noticed a reduction in performance along with the lower fuel mileage? Things like harder starting, rough idle, surging at steady speeds, abnormal transmission shifting? Most problems that effect fuel mileage also effect performance like vacuum leaks, restricted intake air flow, restricted exhaust, low tire pressure, transmission slippage, worn fuel injectors or leaking injectors or worn engine components like piston rings, camshaft lobes or valves. A few conditions that will effect fuel mileage but may not effect performance is a higher percentage of methanol in the gasoline you're using or a partially contaminated oxygen sensor. As you see, there's no easy answer. Also, how many miles are on it?
 

S33k3r

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You might also take a look at the belts. I had a Crown Victoria with a failing alternator that was costing me about 1-1.5 mpg. Once it finished dying (which is how I figured out it was a problem...), I replaced it and my mileage jumped up.
 
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