Leak Down Test

[4N2NR]

A compression test will tell you how well the engine makes compression and whether or not everything is sealing correctly on the compression stroke as far as the rings and valves are concerned.

However you can have a very good compression result but still have poor leakdown results. Leakdown will tell you if and where you may have a potential problem in either your piston rings, valves or headgasket where the compression test cannot.

A typical leak down test tool is approximately $60 (but I don't know how often you would use one). You will need a source for supplying compressed air. Buy or borrow a compressor.

1. Pull the MPI (MultiPort Injection) fuse. This cuts power to the injectors so they don’t spray gas all over the place.
2. Remove all the spark plugs.
3. Using a socket wrench on the crank pulley, turn the motor over until cylinder #1 is at TDC (top dead center) and install the leakdown tester on cylinder #1.
4. Once the leakdown tester is installed on cylinder #1, connect the hose to the gauges and apply compressed air to the cylinder.
5. Turn the adjustment knob until there is 100psi on the input gauge.
6. The actual leakdown result can be read off the second gauge.
7. Anywhere from 0%-10% leakdown is acceptable. Typical readings are around 2%-6% leakdown.
8. If the reading is greater than 10% listen to where the air is leaking from. If it is leaking from the bottom end, then the rings are shot. If you open the throttle plate and hear air escaping, then the valves are probably bent or not seating. If you remove the radiator cap and air bubbles appear in the coolant, then your headgasket is blown.
9. Repeat process on each cylinder.