P0300 /03 CHEV SILVERADO HD6.0L

  • Tiny
  • jje
  • Chevrolet Silverado

I have a 03 silverado with a reoccuring code p0300.I have changed wires and plugs. The code will only set after 25-50 miles of extended highway driving at normal sppeds(65-70mph). You can drive this around town and short distance on the highway for months with no code being set.I have looked at history misfire counts and cyls 1, 5, 8 all show a high misfire count. Over the last year we have change to ethanol gasoline(no more mtbe).I have changed alot of injectors lately becuase of this new formulated gas.I just wanted a second opinion. Ac/delco injectores are about $80.00 ea.X=$640>00. Any ideas? Thanks. Jeff

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Wednesday, December 20th, 2006 AT 6:15 PM

3 Replies

  • Tiny
  • garfield
  • Member

You may want to check for several things; faulty coil (pack), faulty oxygen sensor(s), faulty fuel injector(s), burned exhaust valve, faulty catalytic converter(s), stuck/blocked EGR valve/ passages, faulty camshaft position sensor and lastly a defective computer(but highly unlikely).

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Saturday, December 23rd, 2006 AT 6:24 AM
  • Tiny
  • gjbetzel
  • Member

Any luck with your 03? I have an 01 with the same problem: an erratic flashing MIL at highway speed, and misfire counts on #1 and #6. Engine runs great otherwise, no real misfire.

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Friday, January 5th, 2007 AT 7:12 PM
  • Tiny
  • Service Writer
  • Expert
  • 9,254 posts

Maybe just carbon coated valves?

I would try what I call an air induction service.
I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have somone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushngs. Seafoam is another good product, but smokes a lot.

IF you can't find Castle, here is my rep's email:
robw@castlepackspower. Com

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Friday, January 5th, 2007 AT 7:42 PM

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