HOW TO DO A COMPRESSION CHECK ON YOUR SUPRA
(detailed from the factory Toyota service manual)

If there is lack of power, excessive oil consumption or poor fuel economy, measure the compression pressure.

1. WARM UP AND STOP ENGINE
Allow the engine to warm up to normal operating temperature.

2. NON TURBO SUPRA (2JZ-GE):
DISCONNECT DISTRIBUTOR CONNECTOR

3. TURBO SUPRA (2JZ-GTE):
DISCONNECT CAMSHAFT POSITION SENSOR CONNECTORS

4. 2JZ-GE:
DISCONNECT HIGH-TENSION CORDS FROM SPARK PLUGS

5. 2JZ-GTE:
REMOVE IGNITION COILS ASSEMBLIES

6. REMOVE SPARK PLUGS

7. CHECK CYLINDER COMPRESSION
(a) Insert a compression tester into the spark plug hole.
(b) While cranking the engine, measure the compression pressure.
HINT: Always use a fully charged battery to obtain engine revolutions of 250 rpm or more. (c) Repeat steps (a) through (b) for each cylinder.

NOTICE: This measurement must be done in as short a time as possible. Typically 3 to 5 seconds is sufficient.

Standard pressure:
2JZ-GE : 1,275 kPa (13.0 kgf/cm2, 185 psi) or more
2JZ-GTE : 1,079 kPa (11.0 kgf/cm2, 156 psi) or more

Minimum pressure:
2JZ-GE : 1,079 kPa (11.0 kgf/cm2, 156 psi)
2JZ-GTE : 883 kPa (9.0 kgf/cm2, 128 psi)

Difference between each cylinder:
98 kPa (1.0 kgf/cm2, 14 psi) or less
d) If the cylinder compression in 1 or more cylinders is low, pour a small amount of engine oil into the cylinder through the spark plug hole and repeat steps (a) through (b) for the cylinder with low compression.

• If adding oil helps the compression, it is likely that the piston rings and/or cylinder bore are probably worn or damaged.

• If pressure stays low, a valve may be sticking or seating improper, or there may be leakage past the gasket.


NOTE:
In addition to a compression check, we recommend you also do a leak down test to properly diagnose any internal engine issues.

What is a "leak down" test?

An engine leak down or "cylinder leakage" test is similar to an engine compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss.

A leak down test requires the removal of all the spark plugs. The crankshaft is then turned so that each piston is at top dead center (both valves closed) when each cylinder is tested. You can start with cylinder number one and follow the engine's firing order. Remember to put the piston at TDC before you test that cylinder.

To conduct the test, you need some sort of a "leak down tester". This is usually a threaded coupling attached to a leakage gauge. This tester is screwed into a spark plug hole and compressed air (80 to 90 psi) is then fed into the cylinder.

An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.

The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the exhaust side port, it indicates a leaky exhaust valve. Air coming out of the the intake side or throttle body would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.

A leakage test can also be used in conjunction with a compression test to diagnose other kinds of problems.

A cylinder that has poor compression, but minimal leakage, usually has a valvetrain problem such as a worn cam lobe, broken valve spring, worn valve stem seals, etc.

If all the cylinders have low compression, but show minimal leakage, the most likely cause is incorrect valve timing. The timing belt or chain may be off a notch or two.

If compression is good and leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery (bad injector) or ignition problem (fouled spark plug or bad plug wire or coil).

note:
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