PO300 Missfire code for constant misfires on # 5 & 6 of a 01 8.1L

Discussion in 'GM Powertrain' started by bvartyak, Dec 17, 2010.

  1. bvartyak

    bvartyak New Member

    I've got a 01 silverado with an 8.1L that the problem origionally started as a random Crank with no start. It would be totally random too. You could drive it all day then shut it off and it wouldn't start 5 min later. but then 20 min later it will start no problem. does it cold or hot. fuel pressure requlator is good. NOW i started it up this morning and it is runing really rough!!! Check engine light is flashing. Checked the code and it is PO300. Miss fire detected was on cylinders 5 and 6. More on 6 then 5 but 6 is constant misfire and 5 will stop misfiring above about 2 thousand rpms. Any ideas?

    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    With a Random Multiple Mis-Fire.....It Means that one or more of the following has happened,
    • Faulty spark plugs or wires
    • 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
    • Defective computer
    I would Check the Plugs/Wires first........and then go from there.....also Check all the Wiring and Connectors that lead to the Cylinders.
    Last edited: Dec 17, 2010
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Ditto to above especially if you havent done a tune up recently. And remeber to Run AC delco plugs.
  4. bvartyak

    bvartyak New Member

    I found the problem. It was a faulty Crankshaft Postion Sensor.... NEVER wanna have to replace one of those again! To anyone who ever has to replace one, big help if you can soak it down with penetrating oil for a couple hours!!! The two "O" rings were both seised right up. Could barley even twist it back and forth. Put some penetrating oil on it over night and it came out and had the new one in in about 15 min the next morning. Also be very carefull if you try to pry it out with something!!! I learned the hard way by breaking the top of the sensor off right at the top "O" ring!!! Luckely vice grips would hold onto the electrodes good enough to pull it out!!!

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