Leak Down Test
The leakdown test is another way of measuring the sealing capacity of the cylinder. The basic concpet is to feed shop air into the spark plug hole while the piston is at TDC on the compression stroke, and to see how much pressure it can hold.
If you don't want to spent the $100 on buying a leakdown tester, you can make your own.
http://en.wikipedia.org/wiki/Leak-down_tester
The tester has the following components, in order:
1) Shop air supply, regulated to 100psi
2) Pressure guage to read the pressure that the shop air is supplying
3) Damper valve between the pressure guages to keep the pressures seperate
4) Pressure guage to read the pressure of the cylinder
5) A quick-release to allow the spark plug fitting to be threaded in easily, then connected to the air supply. Without this you will have to turn the whole tester as you screw it in!
6) A threaded fitting to screw into the spark plug hole. This has to be straight, about 9" long for the deep spark plug wells in the maxima.
The parts can all be purchased from hardware store (1/4" NPT brass fittings) for about $20 - except the damper valve. All this is is a tube section inline with the tester between the guages that has a severe restriction. This helps keep the pressures from equalising on the two guages - for the test you want to read the difference in pressures. I made a damper valve by plugging a 1/4" NPT male-to-male fitting with solder then drilling a 1mm hole in it.
Steps to test (allow 1-2 hours):
1) Remove the fuel pump fuse then run the engine till it dies. Remove all coil packs and spark plugs. Open the oil filler, the radiator cap and prop open the throttle.
2) Rotate the first cylinder to TDC on the compression stroke using a wrench to turn the crank pulley clockwise.
3) With the shop air supply regulated to 100psi, and the engine locked in place using the wrench on the crank pulley, apply the shhop air.
4) Read the lower guage, it should read 80-100 psi. (80psi = 80%, therefore 20% loss. 95psi = 5% loss)
5) Listen to where the air is escaping to.
6) Repeat 2-5 on the remaining cylinders.
The loss should be less than 20% - any more than that is bad. More that 40% loss means you are doing something wrong, or your engine is crap. Less than 10% is great. Less than 5% is spectacular. 0% loss on a road engine means you must be doing the test wrong, because no engine can be that good, not even a racing engine.
5-20% loss, with the air escaping through the oil filler, is normal and good.
Any air escaping through the exhaust means you should suspect a poorly sealing exhaust valve. Similarly, air escaping through the throttle body means poorly sealing intake valve. Air coming through the radiator means bad head gasket.
The leakdown test is a good follow-up test to a compression check. It will help you pinpoint problems that exist, but also give you a better idea of the cylinder's condition than a compression check alone. A compression check can give artificially good numbers if you crank too many times, or if you have fluid pooling in the cylinder (leaking oil or fuel). Also you can get artificially high numbers from carbon buildup. If your engine passes a compression check AND a leakdown test then you can rest assured your engine is in good shape.