Do a compression test first. There is a difference between the two tests. If you did a compression test and your results are more than 14 psi difference between cylinders or any of the cylinder are below 130* psi. then do a leak down test to help pinpoint things. These numbers only apply to turbo motors.

See some of us domestic guys do know a thing or two about motors with less than 8 cylinders.

Hope this helps.