Miss fire at # 5 cylinder only under load

Discussion in 'Engine Performance + Maintenance' started by [email protected], Sep 10, 2019.

Car Parts
  1. makindust2@aol.com

    [email protected] OBS Enthusiast

    Messages:
    89
    Likes Received:
    1
    Joined:
    May 12, 2014
    Any ideas? tried new coil new injectors switched ignition wires checked and changed crank pickup.
    All checked out but miss still there only under load
    Skip
     
  2. honkon

    honkon OBS Enthusiast

    Messages:
    180
    Likes Received:
    64
    Joined:
    Mar 19, 2017
    Location:
    Tennessee
    Compression test?
     
    Schurkey likes this.
  3. Schurkey

    Schurkey I'm Awesome

    Messages:
    923
    Likes Received:
    374
    Joined:
    Jan 14, 2018
    Location:
    The Seasonally Frozen Wastelands
    WHAT MODEL YEAR?

    WHAT ENGINE?

    Faulty spark plug?

    Faulty distributor cap?

    Vacuum leak into intake manifold, perhaps from a vacuum port on the #5 runner?
     
    honkon likes this.
  4. makindust2@aol.com

    [email protected] OBS Enthusiast

    Messages:
    89
    Likes Received:
    1
    Joined:
    May 12, 2014
    1997 chevy Tahoe 5.7 checked all of these new plugs and checked resistence before installing
    Checked cap no problems. and vacum is correct .
    I am really stumped
     
  5. L31MaxExpress

    L31MaxExpress I'm Awesome

    Messages:
    660
    Likes Received:
    186
    Joined:
    Apr 21, 2018
    Location:
    DFW, TX
    Check out the GM TSB for sticking valve guides. I had a similar issue with one of these engines only while towing. Ended up having 2 exhaust valves that had the valve to guide clearance so tight they would stick when the exhaust valves got hotter than normal under load.
     
    fancyTBI likes this.
  6. makindust2@aol.com

    [email protected] OBS Enthusiast

    Messages:
    89
    Likes Received:
    1
    Joined:
    May 12, 2014
    Brand new heads also . I had cracks in both. Not because of any overheating or anything.
    They were a set of remanufactured heads but must have got passed inspection .So I bought a new set from GM.
     
  7. stutaeng

    stutaeng OBS Enthusiast

    Messages:
    58
    Likes Received:
    6
    Joined:
    Aug 7, 2019
    Location:
    Dallas, TX
    I would do a compression test next. Might reveal a blown head gasket, but doesn't sound like it. Did it just start doing this?

    Could it be an injector causing misfire?
     
  8. stutaeng

    stutaeng OBS Enthusiast

    Messages:
    58
    Likes Received:
    6
    Joined:
    Aug 7, 2019
    Location:
    Dallas, TX
    I would do a compression test next. Might reveal a blown head gasket, but doesn't sound like it. Did it just start doing this?

    Could it be an injector causing misfire?
     
  9. makindust2@aol.com

    [email protected] OBS Enthusiast

    Messages:
    89
    Likes Received:
    1
    Joined:
    May 12, 2014
    Compresstion is perfect, Did new injectors also and check out
    Skip
     
  10. Eveready

    Eveready I'm Awesome

    Messages:
    660
    Likes Received:
    326
    Joined:
    Nov 29, 2017
    Location:
    North Carolina
    There was a thread here sometime back about a distributor getting out of kilter under load. I think it was a bad bearing or something and the truck would run rough when under load but at no other time. I wonder if you don't have early symptoms of that issue. I have no idea how you test for it but surely someone will have an idea. Good luck!
     

Share This Page