if there is lack of power,excessive oil consumption ,poor fuel economy and engine abnormal missing ,measure the compression . if engine compression is very low then engine will not start.
to check the engine compression pressure first start the engine for 5 min.you must need a full charge battery .disconnect ignition & fuel system then remove spark plug and insert the compression gauge tight it properly .press full accelerator pedal and cranking engine for 10sec .measure the pressure .compression pressure very model to model so please check the model specification .for petrol engine difference between each cylinder 95kpa/14psi or less .
two type of compression test done in this video dry type and wet type and step by step i m try to show you with diagnosis.