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Message: <blockquote data-quote="shiroitenshi" data-source="post: 2510321" data-attributes="member: 27518">white/bluish smoke is usually a sign of unburned fuel, either from too rich a fuelling (unlikely if you aren't running higher fuel pressures or had the car tuned by someone incompetent)It can also mean valve leakage. You can do a compression test to verify which piston's vavle is the source.Valve leaks means that during compression stroke, the unburned fuel is pumped out the exhaust valve or into the intake tract via the intake valve instead of being properly ignited by the plug at BTDC. on the next stroke, the engine runs too rich, and unburned fuel exits through the exhaust.The O2 sensor detects that the engine is running lean (O2 sensors detect unburned fuel as air, so it inteprets the engine as running lean, and increases fuelling, so when you take out your plugs, you'll see that it's all black/fouled, a sign of too rich a fuelling.)Piston ring seal can be gauged by looking at black smoke emitted through the exhaust, and listening to air escaping through the oil cap when manually rotating the crank. (but only if your valves are not the source of the leak)The amount of oil burned/the amount you need to top up between oil changes is also a sign of piston ring leakage. due to the stock setup of piping engine oil gases in the head to the intake pipe, vtec engines consume a nominal amount of oil even at peak condition, so note the amount of oil you need to top up, if it increases substantially, there's a possible piston ring leak that a leakdown/compression test can confirm.However this is unlikelier than valve leaks, because unless your engine ingests something, the bore should not be too affected, and we have 2 compression rings and an oil ring to boot on the stock piston! so that's it, unless you're using single ring racing pistons.. (O_o)Then again, I'd start with the valves, then check the rings. Due to the way they are related, you have to ensure that the valves aren't the source of the leak, then only troubleshoot the piston rings.Annealed rings are also a possible cause of piston ring leaks, but that's also a sign of trouble elsewhere, so if you have annealed piston rings when you stripdown, look for possible sources of engine overheating to the point the rings are annealed.There's also the method of removing each plug cable one by one to find out the problematic piston/valve leak, but due to the inherent dangers of dealing with high voltage, leave it to the professionals.These are all mechanic stuff, so if you mechanic knows what to look for, he should be able to decide the best course of action.</blockquote>