Cadillac Repair: Engine knock 99 Cadillac, piston skirt, combustion chambers

Question
I have a '99 Caddy Deville( purchased new) 44,000 miles on it. I get a rattle when slowly starting from stopped position. This noise is intermittant and resembles rod noise when it happens. Cad. dlrs. tell me nothing is wrong. I have cleaned combustion chambers in accordance with Bulletin No. 99-06-01-010C.No change.
Any Ideas?

Answer
Hi John, I'm not famillar with that bulletin but if it involves putting top engine cleaner into the cylinders and letting it soak over night then sometimes you have to do it 2 times in order to clean things out. If the noise just started happening then maybe the quality of gas you are useing is the problem. The Northstar engine is designed to run on premium and will knock/rattle or have pre ignition/detonation that might sound like rod noise if 87 or 89 is used. Did you try a differant brand of gas for a tank or two and see if that makes a differance? At the dealer they have a scan tool that can check what octane the computor thinks the engine is running on. If it shows 92/93 then your noise could be due to a mechanical failure such as worn bearings, loose piston connecting rod pin, piston skirt too small to name a few things. Caddy had some problems with the piston skirts where they wern't the right size and until the engine warmed up it made a knock noise. Without hearing the rattle myself it is kind of tough to determine what might be causing it. Bill