Knocks and Falters

Discussion in 'GM Powertrain' started by wherewasi, Aug 19, 2010.

  1. wherewasi

    wherewasi New Member

    Hi, King of the Newbie's Here.

    I have a 99 Silverado 1500. 5.3L Auto. Truck has 140K Miles. I got it at around 75K.
    Love the truck; it's starting to need some TLC.

    Recently got the MAF code and cleaned the MAF and it did help some with sluggish acceleration off the line. But did not eliminate it completely. I also get knocking at highway speed after the truck is warm. I've downloaded all the Chevy stuff and looked around at the forums. Seems like this could be caused by many things.

    The question is... where do I start? Not getting any further 'code' clues. Could it be any one of all those sensors? (Knock/MAP/IAC etc?) Is a good cleaning in the right spots gonna help?

    Can't stand the idea of going to my dealer who has really screwed me a couple a times... even wrecked the truck once. Any assistance greatly appreciated. Also, hate to even ask... but if you avoid abbreviations I'll be better able to understand ur advice.


  2. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    I would try cleaning the MAF with CRC MAF cleaner. DON'T use throttlebody cleaner. CRC is the only company that I know of that makes the MAF cleaner, it's in a silver can.

    ---------- Post added at 01:47 PM ---------- Previous post was at 01:46 PM ----------

    I forgot, welcome to the club.
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Let me start off with welcome aboard! Also to echo Silver be sure to use CRC MAF cleaner.
    Also I would try and clean the pluggs and the knock sensors just to be sure.. The IAC (idle air control valve) will cause a major stumble etc at highway speeds and off the line. So if you have a little hesitation i would go ahead and clean out the Throttle body. Also have you done a Seafoam treatment? I would go ahead and suck some up via the brake booster line. And let it sit for at minimum 45minutes... And is it Pinging or is it a metal on metal Knock at highway speeds? Becuase if it is metal on metal there is a chance it is Piston slap, bad bearings, Or else the Incedibly notorious Lifter clatter that the 5.3L is famous for.
  4. wherewasi

    wherewasi New Member

    Thanks... will do.

    ---------- Post added at 10:40 AM ---------- Previous post was at 10:38 AM ----------

    Mike, I'm pretty sure it's valve clatter. It only seems to happen after the truck's warm.
    I will try the seafoam thing. I've read some on that. Where's the brake - booster line? Does it vacuum into the intake?

    ---------- Post added at 10:50 AM ---------- Previous post was at 10:40 AM ----------

    I see ... it's on the back of the throttle-body/intake assembly
  5. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Yep you will remove the line (which runs from your intake to the brake booster) and start the engine and obviously revv it up a touch, and pour the seafoam down the line. And let it sit for a minimum of 45 minutes... No less because i have done 30 min before and it really didnt do anything so i tried 45 and it did a little.. an hour or more if you have time to kill really is the ticket.
  6. wherewasi

    wherewasi New Member

    I leave the engine running while the seafoam is in there for over an hour? or suck it in and shut 'er down? Sorry if they seem like dumb questions... I am largely ignorant... for now.
  7. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    No problm you will shut it down.. And let it sit for an hour... So it can break up the carbon that is built up... Then take it for a drive about 5 miles is my usual loop when i put it in there.

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