bought a ls400 and the so called mechanic rigged the power steering pump to work when i installed the new pump power steering worked fine now the problem is that it smokes very bad from the exhaust what could it be

What color is the smoke?

What color is the smoke?
white

White smokes indicates coolant is being burnt....could have a bad/leaky head gasket.

it didnt smoke before i replaced the p/s pump

You may have popped the head gasket none the less..