Do test with warm engine, and take out the efi fuse in the fusebox that's in the engine bay. Remove one (so you remember what lead goes where) spark plug and make sure you put the tester in properly, not too tight can be hard to get off. When cranking the engine do it with throttle pedal pressed to the floor the whole duration of cranking. Cranking for around 10 seconds is plenty, the compression gauge should be around 10-12 bar and it won't go any higher anyway after its reached max pressure. Write down reading and release pressure in tester, should be a button to do this. Put plug and lead back in and do the same to next spark plug