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TBI 350 knocking up light load??

Discussion in 'The Garage' started by Big89Burban, Nov 20, 2005.

  1. Big89Burban

    Big89Burban 1/2 ton status

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    Hey guys. Having a little problem with my suburban. Its running really strong but I have noticed under a light load it sounds like its pinging. I noticed it mainly when its locked up in 4th. It sounded worse when I was pulling a trailer with it (in 3rd of course). It really sounds like spark knock. I'm using 87-octane. Thought that would be plenty. I dont really know where to start in this thing. Since I got it I've replace fuel filter, plugs, rotor & cap. Its strange cause the CEL does come on and throws code 43(rough running if I remember) but it only does that if I cruize for a while. Under acceleration it doesnt ping or anything. Also I notice it really bad when I cruizing in 4th, locked up and I ease into the throttle trying to get it to downshift. Just before it kicks down you can hear it ping really bad. Then when it downshifts it doesnt do it. :confused:

    Anyone got any ideas? I dont really know how these systems work otherwise I could probably just diagnose it myself.
     
  2. xpndbl3

    xpndbl3 1/2 ton status

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    what is your timing set at right now? and have you tried increasing octane to offset pinging? it might be a certain brand of gas that causes it. you said it has a new tune-up and fuel filter so those can be ruled out. spraying out the intake with upper intake cleaner and removing deposits could help as well.
     
    Last edited: Nov 20, 2005
  3. Big89Burban

    Big89Burban 1/2 ton status

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    See the thing is it pings when I least expect it (cruizing). If something were wrong with base timing then I would expect it to ping under hard throttle but it doenst.

    A guy that I work with used to be a chevy tech. and he said that it was probably carbon build up, but I'm not so sure..
     
  4. xpndbl3

    xpndbl3 1/2 ton status

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    then get some upper intake cleaner and some seafoam from the auto parts store to clean it out.
     
    Last edited: Nov 20, 2005
  5. Big89Burban

    Big89Burban 1/2 ton status

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    I was kinda hoping it was a common prob. or something. I searched around a bit and didnt really find anything helpful.

    Plus the chevy guy.. well lets just say he's a hack. Not really the strongest diagnostic tech. I've worked with and Im pretty sure he never worked on any older chevy stuff such as my truck.
     
  6. xpndbl3

    xpndbl3 1/2 ton status

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    sounds like too much timing causing a lack of knock sensor retard.

    try out $10 worth of intake cleaner and a can of seafoam first. if not try better gas, then try the more expensive stuff.
     
  7. diesel4me

    diesel4me 1 ton status Premium Member

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    might try..

    Check the EGR valve and make sure its working--it might be its got a hole in its diaphram,no vacuum getting to it,or carbon build up under it in the passage in the intake,rendereing it inneffective..not having it working will encourage pinging..if its running hot it will ping easier too...might be poor gas octane too.. :crazy:
     

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