put it in idle and then put a dollar bill over hte exhaust tip. if your exhaust is not leaking, and the valves are good, the dollar will rhythmically flap. if the dollar pops, you have burned valves.
if you have someone start it in the morning with you watching the tail pipe and blue smoke comes out at start up, the valve seals leak a little while sitting. it if smokes on deceleration, blue smoke, the valve seals are leaking.
if it smoke while driving or idling, all the time, and is blue smoke, the rings are not sealing properly and you will probably have low or bad compression on some cylinders or all cylinders
I don't feel like working on anything at this time so i sold my yj.