Car won't pass smog bloing out blue smoke. Why?

Could be a piston ring/cylinder issue($$$), are you using a lot of engine oil and does it smoke all the time? How many miles are on your vehicle?

Blue smoke indicates burning oil. Along with the possibility of worn piston rings it could also be the valve guides or valve guide seals leaking oil past and into the combustion chamber. the rings would be an expensive fix. you would need an engine overhaul or rebuild. The valve guides being worn would mean the head would have to come off and need rebuilding. Valve guide seals can almost always be replaced without removing the cylinder head if you hae the proper tools. but most shops would try to convince you to rebuild the head. Another possibility is that the oil is being drawn into the intake manifold through the PCV (Positive Crankcase Ventilation) System. If the PCV valve is stuck open or the crankcase vent is plugged it would allow the engines vacuum to draw oil from the engines valve cover into the intake and burn it in the combustion chamber. With the engine shut off pull the hose off the PCV valve and see if there is oil setting in the hose. If there is you may have located your problem and that would be an inexpensive fix.

You have an oil leak from one of several possible sources. Bad PCV or pollution control valve, bad piston valve or leaking gasket. See a mechanic and have it fixed and your car will pass next time.

If you dont want to put money into the vehicle but want to stop it from burning oil you can go to any parts store and buy an additive that will give you a temporary fix, just tell the sales person your situation and he will recommend an additive.