No compression number six cylinder

If I am not mistaken this active fuel management is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. Chances are if one cylinder is low or zero, either an intake or exhaust valve is stuck open or there is a blown head gasket. It could also be a hole in the piston top. I would perform a cylinder leak-down test in order to listen where air is leaking out. That piston will have to be set at TDC compression stroke so both valves would normally be closed, then remove the spark plug and apply air. Then listen to where the air comes out, if out the tailpipe then an exhaust valve not seating, if out the throttle body then an intake valve not seating, if out the oil fill cap, then perhaps a hole in the piston or a blown head gasket and if bubbles in cooling system then again, blown head gasket.

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