Engine was running well. It hasaGM8 turbo on it( previous owner). Started blowing black smoke, then grey with a little white every now an then. Lost a lot of power, to the point it barely pulled itself. Boost gauge read vacuum. Changed turbo out Still blowing smoke-maybe not as black,still grey, some white. low on power. Not sure of next move. It starts very well. Idles smooth. Goes funky at throttle. Help?