Ryan,

Here is very well written procedure for performing a compression test. I'm sorry I can't give the author credit- he posted it here on the Brickboard and I downloaded it to my file and I don't have his name with it.

Randy

1. Unless you're checking for poor starting due to serious low compression when cold, the engine should be at or near normal temperature. With aluminum heads, plugs should be loosened only when cold and then lightly seated to warm it.

2. Disable the ignition system and

prop the throttle linkage open <--(common mistake).

Hint: pull the coil wire and rubber band it to/near the linkage so you won't forget to undo the propping before restarting the engine.

3. Use a helper, a remote starter button or position the gauge where you can see it while cranking.

4. Screw compression gauge hose into a cylinder and WATCH the reading on the first stroke. This is closely related to the dynamic pressure when the engine is running and indicates the sealing ability of the RINGS during the compression stroke. It should be at least 75 PSI and somewhere between 75-80% of the final reading.

Let the engine crank for a total of FOUR strokes, not 3,not 5, not 18. This indicates the ability of the rings to seal during the POWER stroke and the integrity of the valve-to-seat seal. Most people crank until the reading stops rising. This skews the results. You're looking for balance between cylinders, so you have to test each one the same way.

If you miss the first stroke reading, see the gauge jump the instant the engine spins, or zip past the fourth stroke - release the pressure and retest that cylinder.

Record the guage reading.

Rule of thumb; final reading below 100 PSI with normal (non-racing) camshafts, below 5000', on an engine with a compression ratio between 7.5-9.0 to 1, is too low for dependable starting and good economy. (Don't be getting too worried here - your turbo motor is right down at the low end of that range [mid 7s] so it's not so bad).

I generally record both the first and fourth stroke readings for comparison.

5. Move the gauge to the next cylinder and repeat.

6. When one or more low dry readings warrant performing a wet test, use the pump type oil can and be sure to squirt the SAME amount of oil into each cylinder. Crank the engine one or two times before screwing the gauge into a cylinder just oiled. No need to check to first stroke reading in this test. You're looking for the amount of improvement over the fourth stroke reading of the dry test. A 10-15 PSI rise is normal. If you start a wet test, check all cylinders, not just a low one.

A big jump in readings indicates that the oil is sealing weak rings. Very little change, only where a dry reading was low, would indicate leakage elsewhere...usually valves, but head gasket leakage would give similar results.

A similar rise between cylinders indicates even wear, and may warrant no further investigation.

7. Reinstall spark plugs, unjam throttle, reconnect ignition system, check hoses, etc. that you moved while servicing the car, start engine, close hood.

8. Put away tools, get cold beer or dinner.

After all that...you may find smaller (or larger) differences between cylinders. The readings you started with indicate good valve sealing and slightly worn compression rings. Unless your 16 year old car is pristine, and the compression loss has really taken its toll in power or gas mileage - you can save yourself a whole lot of money and labour by leaving the guts alone and keeping up with the regular maintenance.

In other words, don't fix what may not be broken.

PS for other readers; You cannot perform a "dry" test after doing a "wet" test without putting things back together and running the engine to burn off the oil.