Re: leak down test
you will need a compressor that will pump up to 100psi. Probably something will a small tank.
pull all the plugs and turn each cylinder over as if you were setting the motor at TDC but for each cylinder (you can also use a pen light to visually see the position of the piston). The leakdown will tell you if the cylinder is leaking into the oil pan, exhaust, intake, cooling system etc. Then you will know if it is a headgasket, bad rings/broken piston, valve seal, etc.