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Alright So today I started up my car and heard a knocking noise. Not the first time ive heard my engine knocking but it normally only does it in the winter and by the time the engine warms up it goes away. First time the car had been started in about 4 hours but it wasnt that cold outside either but I hear it knocking and decide to rev it up a bit to warm the engine. Sure enough I see a bunch of smoke coming from my exaust, though once I started driving it stopped. Should I be concerned?

 
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The knocking is probably your injectors, its fine. If your car smokes blue at start up, but then it seems to burn off, that's usually a sign of leaky valve seals, but only a compression check will tell you.

 
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Are my injectors going bad or something? Never heard of injectors causing a noise like that. I havn't had the smoking problem since but if I do Ill have a compression check done(Is it hard to change the valve seals?)