2001 Chevy Silverado 5.3 code P0300 help

Discussion in 'General Chevy & GM Tech Questions' started by 1quick6, Jun 24, 2010.

  1. 1quick6

    1quick6 New Member

    I have a 2001 Chevy Silverado Z71 with a 5.3L v-8 that I am trying to fix. It has 70k miles on it. The truck had an intermittent P0300 random multiple misfire code that would trigger the check engine light a few times a week. The truck can be a little hard to start and smells a bit gassy at startup. I originally suspected the plugs/wires, so I bought a new set of delco wires and delco iridium plugs. As I was removing the old plugs, they were all normal with the exception of one cylinder, which was the passenger side second cylinder from the front. That plug was black and sooty. I put all new plugs and wires in and started the truck back up. After a few minutes of ldling, the P0300 code came back. I pulled the suspect plug and it was again black while the cylinder next to it was nice and normal.

    The coil seems to be ok on that cylinder since it sparks regularly against the exhaust manifold when testing. Is there a way to test the coil on that cylinder to get a definitive answer? I have a multimeter.

    At this point, I am suspecting the coil or an injector that is stuck open causing that cylinder to be very rich. Most people are telling me stuck injector based on 7 plugs being normal and one being black. These seem like great forums, so I figured I'd see what the fine people here had to say. I plan on doing a compression test just to see how that cylinder looks compared to the others. I guess it could also be EGR related. P0300 is such an ambiguous code.

    Last edited: Jun 24, 2010
  2. 1quick6

    1quick6 New Member

    Nevermind, I guess.
  3. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    Hook up a fuel pressure gauge and see if the preasure drops after you turn the engine off. If it drops most likely a leaky injector.
  4. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    The 5.3's have one coil per cylinder, right?
    You could test the "bad cylinder's" coil by switching it with a good cylinder's coil. If the bad cylinder's plug -get a new one or clean it very well- is sooty, you know it isn't the coil, it is probably the injector.

    PS How much is an injector? Sure sounds like an injector.
  5. 1quick6

    1quick6 New Member

    I actually did fix it yesterday. I said nevermind because I was surprised it had gotten that many views and no responses. :)

    I did a compression test and a vacuum test and it did fine on those. Then, I tested the resistance on the coils and they all gave similar readings within spec. I still suspected the injector but I didn't want to take the fuel pressure gauge off my 87 Grand National to check, so I pulled the fuel rail on the passenger side and pressurized the system. Sure enough, drip drip drip on the #4 injector. I ended up buying a rebuilt injector from Rock Auto for $35. I was not paying over $100 for a new one.

    The truck started right up and runs like new again with no codes.
  6. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    $35- price was right-$100, not so right!
    Glad it worked out ok.
    Usually lots of looks but no replies means either folks agree with your guess-injector- or they have no freakin idea!
    The sooty plug and gas odor probably made folks think as you did-bad injector.

    I don't think coils die that often, but injectors sure do!


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