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Re: Knocking noise
Combustion chamber deposit interference (CCDI) and combustion chamber deposit flaking (CCDF) are two other problems which sometimes occur in certain modern engine designs. CCDI is the result of physical contact between deposits on the piston top and cylinder head and is manifested as a loud, metallic banging sound when the engine is cold. CCDI is limited to the engines that have been designed primarily to reduce emissions, with minimal clearance—one millimeter or less—between some areas of the piston top and the cylinder head (squish areas) when the piston is at top dead center. Combustion chamber deposit flaking causes low-compression pressures to result due to improper sealing of the valves. This problem occurs when pieces of CCD flake off and end up lodged between the valve face and the valve seat. Typical symptoms of CCDF are difficulty in starting and rough running when cold.
You have to run some fuel system cleaner thru but not the cheap 2.99 stuff on the shelves of discount stores. They won't do it, most of that stuff is to weak to do anything, its more preventative. Go to the GM dealer and buy GM fuel system cleaner and follow the instructions to the letter. You add to tank, fill up and drive till empty. If you top off tank, you dilute the cleaner and effectiveness. BTW-Price range at dealers is $15-$25 per bottle. Its basically Techron in a sized bottle for GM applications. Look for Techron but you may need to buy two bottles. I think the GM bottle is 20oz.
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Mike
2008 GMC Sierra SLT E. Cab Z71
2005 Cadillac CTS 3.6L
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