Slow to respond knock sensor maybe?
Question about GM knock
- Thread starter TomH
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We've tried a number of things including Fuel Power and no change. Literally nothing we have ever done has changed the sound.
What I don't understand is that IF it's piston-slap then it should go away as it warms up. At idle it's got awesome oil pressure, so that doesn't seem right. When it first starts up (hot) it knocks, and the slightest RPM rise makes it go away and it doesn't come back. I use the word "knock" for the noise but it doesn't sound ignition related.
At 600 rpm or whatever these idle at you can actually replicate the noise yourself, perhaps 10 per second or less.
My pop's 2002 Suburban has the 6.0L.
For the last 20K miles, his has knocked loud enough to sound like a diesel (and old-school diesel, too), but under unusual circumstances.
He's tried various grades of Mobil-1, and Chevron Supreme. Nothing made any difference at all.
Of course it knocks quite a bit when cold, but here's the kicker.
After 90 minutes at highway speeds, we stopped for 5 minutes. He started the truck back up and yep, it knocks. Give it some gas for a slight RPM rise and it goes away and doesn't appear to come back. It doesn't *sound* like piston slap, either, although it's hard to tell.
What could it be? It *almost* sounds like a lifter isn't pumping up.
For the last 20K miles, his has knocked loud enough to sound like a diesel (and old-school diesel, too), but under unusual circumstances.
He's tried various grades of Mobil-1, and Chevron Supreme. Nothing made any difference at all.
Of course it knocks quite a bit when cold, but here's the kicker.
After 90 minutes at highway speeds, we stopped for 5 minutes. He started the truck back up and yep, it knocks. Give it some gas for a slight RPM rise and it goes away and doesn't appear to come back. It doesn't *sound* like piston slap, either, although it's hard to tell.
What could it be? It *almost* sounds like a lifter isn't pumping up.
there is a law suit going on in California about the 6.0 knock...GM says it's normal...what might help a little is going to 91 octane with 15-40 diesel oil...it did work a lot better in my 454...
Propflux01
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What are you guaging that from? external guage or factory indicator?
Run a can of GM Top Engine Cleaner thru the intake per the instructions on the can. If you can't dump it down the throttle body, remove a small vacuum hose and draw it in that way.
Let it soak for 15-20 minutes, then start it up, apologize to your neighbors for the smoke screen, then take it out and drive it like you stole it for about 5-10 miles or so.
Bring it back and change the oil and filter and that should take care of most, if not all of it.
Let it soak for 15-20 minutes, then start it up, apologize to your neighbors for the smoke screen, then take it out and drive it like you stole it for about 5-10 miles or so.
Bring it back and change the oil and filter and that should take care of most, if not all of it.
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