5.7L suburban misfire issue

Discussion in 'General Chevy & GM Tech Questions' started by maxpayne23, Nov 6, 2011.

  1. maxpayne23

    maxpayne23 New Member

    Two weeks ago I was heading across town when all of the sudden the truck started to misfire. The cats are less than a year old, cap, rotor, plugs and wires were changed at that time too. I had the codes pulled and it was a bank 2 sensor 2 o2 and general misfire.
    I replaced the plugs, wires, and fuel pressure regulator. I separated the muffler from the cats to see if that was causing a restriction and it did the same. Im kinda perplexed at this point. Any points or steps to try next?
     
  2. jmccarrell

    jmccarrell New Member

    There are two other possibilities that would cause this to happen, 1 u need a new o2 sensor or 2 u have a bad objectors. I am leaning more towards the o2 sensor though. U can either clean it, which won't last too long, or replace it. I believe our trucks have 3 o2 sensors. It would be best to replace all three at the same time . You'll.see better gas mileage and a little better performance as well. Good luck!
     
  3. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    If you are certain the code was for O2 sensor 2 on bank 2, I don't know if I would expect that to be the problem. The 2nd sensor on each bank is the post-cat sensor, and its sole purpose is to monitor cat efficiency -- it doesn't really figure in to engine operation. If the codes was for one of the pre-cat sensors (sensor 1), then I'd be more inclined to see the O2 sensor as contributing to the problem.

    The real trouble with P0300's is that there are so many possible causes.
    Because it's quick, I'd probably start by putting a fuel pressure gauge on it and seeing if the fuel system is doing its thing as it should.
    I would probably inspect those new parts (cap, rotor, etc.) to make sure they are still good. I would probably also dig deeper into the ignition system and check things like the coil and the distributor.
    A compression test might be in order to make sure each cylinder is in good condition and that the valves are working.
    They are hard to test, but GM had a lot of problems with the poppet valves used in the CSFI system. If you still have the original spider, it might be worth looking at that.
     

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