1999 Silverado "Banks too Lean"

Discussion in 'Chevy Truck Forum' started by chucky6965, Feb 8, 2008.

  1. chucky6965

    chucky6965 New Member

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    I have a 1999 Silverado and the service light keeps coming on. The truck has 137,000 miles on it I had changed the spark plugs when all this started. I have change the mass air flow sensor, new fuel filter all new oxygen sensors and have checked for any vac leaks using soap and water and sprayed carb cleaner around the intake. The truck runs great and idles good and the gas mileage was poor before I had changed the spark plugs and at that time the gas mileage went up and it still is running good. Its just the service engine light will no go off. Codes received are P0171 and P0174. Both banks too lean… any ideas?
     
  2. 72'CaminoKid

    72'CaminoKid Senior Member

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    i want to say maybe something with hte cats but not positive
     
  3. mudseeker

    mudseeker Senior Member

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    i would check for exhaust leaks before your o2 sensor. also the cat like camino said. what brand of o2 sensors did you buy? most non-oem sensors are junk right out of the box.
     
  4. jdfenske

    jdfenske Senior Member

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    how would one check a vacuum leak with soap and water?

    i beleive the first set of o2 sensors regulate fuel injectors with air intake.

    2nd set check to see if cats are working. i think.....
     
  5. NCroadracer

    NCroadracer Senior Member

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    Most likely it will be your intake seals leaking vacuum... Spraying the intake has little to no effect on it, unless you can watch the Ho2s readings with a scan tool. they usually leak at the bottom of the ports where you can't really spray anything.
     
  6. emzornes

    emzornes Member

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    Banks lean

    Have you checked the fuel pressure yet? That would be where I would start a weak fuel pump causes this very problem and sets the same codes.
     

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