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Brutal Knock and Ping

Discussion in 'GM Powertrain' started by jpgoodnu, Jul 16, 2009.

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  1. jpgoodnu

    jpgoodnu New Member

    I have a 2002 Silverado Z71 with 5.3 and 4L60E. I have a problem with BRUTAL Detonation(sounds like machine gun fire) at wide open throttle,once it gets above approx 4,000 RPM. It is reduced when engine is cold or when using super unleaded fuel,but still bad. I have no "check engine" light coming on, but at one time I was getting a "lean misfire" code,but that hasn't appeared in months. I had the dealer check it 3 times, twice they used the "on vehicle" fuel injection cleaning system and even replaced they entire catalytic converter system. Each time they cleaned the injectors it was better for about 1 week, then it came back. I have replaced the fuel filter myself twice and each time it appears to NOT be loaded with crap(not at all heavy). Any suggestions?
  2. 2COR517

    2COR517 New Member 1000 Posts 100 Posts

    What do you have for plugs/gaps?
  3. Jimmiee

    Jimmiee New Member 1000 Posts 100 Posts

    Get it scanned and check your fuel trims.This will tell you if you have a lean condition. If it's running lean you will damage your pistons and valves. Don't drive it this way because it won't take long to ruin your mill.
    Make sure you take it to someone who knows how to tune an engine using the scanner rather than someone that throws parts at it. It sounds like the dealer was at a loss as to what your problem really is.
  4. jpgoodnu

    jpgoodnu New Member

    I am still running to original equipment AC delco iridium plugs with 96K on them and they show almost no wear at all. The dealer claim s they had their "guru" runa real time scan and "Nothing is out of spec" and it must be carbon build up and they claim that is why their "on the vehicle high pressure injector cleaning service" clears up the problem for about a week,BUT they can't explain why it then comes back or what is causing it in the first place. I have had this problem for over a year and just don't ever "boot it" so it doesn't occur.
  5. 2COR517

    2COR517 New Member 1000 Posts 100 Posts

    Have you tried SeaFoam? A can through the brake booster line and another can in the tank. Wouldn't hurt to clean the MAF and trottle body either.
  6. phoebeisis

    phoebeisis Active Member 1000 Posts 100 Posts

    Weren't the early 5.3 famous for building carbon above the top ring- usually causing a pston slap type noise that made folks think their motor was worn out.

    I know forums were filled with pissed off customers because if this.Apparently it caused no permanent damage.I think the noise was most noticeable at idle.Maybe your motor continued to build carbon, and you have a hot bit of carbon causing preignition, or so much carbon the compression is raised and you have detonation.

    Either way, the Seafoam seems to have worked wonders for lots of folks.It is sure worth a try- maybe using it more than once. I think some folks actually manage to introduce it thru the vacuum brake line.
    Other folks can tell you more about how to use it.

    Luck
    Charlie
  7. silveradotrailblazer

    silveradotrailblazer New Member 1000 Posts 100 Posts

    Theres a fuel system cleaning machine called motor vac. I dont know if its the machine that the dealer used, but if its not try to find a shop that has one. They disconnect the fuel lines and connect the motor vac to the fuel lines and let the truck idle with the chemical running threw the system. It idles for several hours and gives a good cleaning to engine and removes the carbon build up. Fords are bad for carbon build up and I saw older Bronco that would knock and bearly run get cleaned and it was unreal what a differance it made in that Bronco.
  8. jpgoodnu

    jpgoodnu New Member

    I don't know what brand machine the GM dealer used,but both times it made a difference for about a week then it came back and I also had it done on actual MotorVac machine at my buddies repair shop with the same results. I had it to another GM dealer last Thursday and even though they clearly observed the problem when punched above 4K rpm they can't find anything "out of spec" on the scanner even when the problem is actually happening. They also couldn't tell me if they saw a response from the Knock sensors when it was happening. I am suspecting a possible chewed wire in the knock sensor harness(damn rodents take full advantage of any possible shelter) under the intake bacause the truck was parked unused for 4 months before I bought it and there is alittle firewall insulation missing also,just a hunch on my part. I doubt it is a carbon issue with all the crap that has been pumped through that fuel system.
  9. 2COR517

    2COR517 New Member 1000 Posts 100 Posts

    Something is out of whack, for sure. The fact that the carbon cleaning helps for even a week means it is doing something. Given that the truck sat for a while, you might be dealing with crap in the gas tank too. Have you changed the fuel filter? You might even need to pull the tank and clean it out. And definitely look around your wiring harnesses for rodent damage.

    Take a look at this thread. If you clean the TB, you would have a baseline for measuring more carbon buildup.

    http://www.gmtruckclub.com/forum/showthread.php?t=25593
  10. wpnsgy

    wpnsgy New Member

    were is this noise coming from if it is popping into the air intake you could possibly have a cam or valve problem. since it is at a higher rpm might look into weak or broken valve springs

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