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Ok guys 2012 GMC Sierra 1500 with a 4.8 owned the truck since new . I went to my mechanic with excessive fuel consumption, I was always down as the truck is lifted on 35's so I was use to it but past 2 weeks is was extremely bad . He scanned it And said it was reading 30% alcohol and he reset it . But it's getting bad again. You guys have an idea ? Solution? Please move
Topic if posted in wrong section. Thanks
 

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Plug in and read the short & long term fuel trims.
 

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Turn your car off, wait a few min, turn it back on (do not start). Listen for a hum coming from under the rear seat. If you hear it for a few secs, your fuel pump is priming the system and is working. Not to say its free from defect entirely, but if its priming the system, you are getting fuel up to the filter at least. After that, your fuel system may be clogged or your ignition system problematic or even your emissions e.g. the o2 sensor. And for more assistance, you can post in r/cartalk

Tutuapp 9Apps Showbox
 

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Fuel pressure at the rails? Excellent suggestion to plug in at the OBD2 port and check the fuel trims. I'd also look at the MAP sensor numbers, O2 sensor responses and a whole list of things.

Since I can do it for free, I'd try a crank position sensor relearn.

Rick

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