How to do a Compression Test

Compression gauge

You can get one of these for between $15 and $50 almost anywhere you can get auto supplies, including Canadian Tire, Pep Boys, and even WalMart. You don't need a particularly good or expensive one just to make sure you're in spec.

13/16" spark plug socket

Obviously, and a socket wrench, to take out the spark plugs.

4 new NGK BPR6ES spark plugs

In case any of the plugs are fouled. The NGK are the most frequently recommended plugs on the Talon Digest by Club DSM members, so who am I to argue?

Plug gapping tool

If you're not replacing your plugs, and even if you are, you might as well make sure they're properly gapped.

Oil and a funnel

In case you need to do the wet test.

1. Before you begin, make sure the battery is fully charged. Take it for a good hard drive. 5 minutes of idling won’t cut it.

2. Pull the MPI (MultiPort Injection) fuse on the positive terminal of your battery. This cuts power to the injectors so they don’t spray gas all over the place.

3. Unplug the coil connector, it’s on the right side, at the back of the block. You could get a nasty shock if you don’t.

4. Remove all 4 plugs and examine them carefully for signs of a problem. If your valve seals are bad in any cylinder, the plug will be fouled to some degree. Signs of oil on the plugs could indicate a ring problem.

5. Screw the compression gauge into the plug hole

6. Press the gas pedal to the floor to open the throttle plate, and keep it at WOT (wide open throttle) for as long as you’re cranking (if you didn’t pull the MPI fuse, there would be a bit of a mess, now).

7. Turn the ignition to the ON position, and hold it there for a count of four revolutions (do not turn the key on-and-off four times). On each rotation, the gauge needle will jump slightly less than the previous one.

Update: It may take more than 4 revolutions to get a stable reading; crank for up to 10 seconds or until the needle stabilizes, whichever comes first.

Note: If your battery is weak, the engine will turn over slower and give you lower readings.

8. The last number the gauge jumps to is the compression for that cylinder.

9. Repeat for each cylinder.

1G (90-94) T/E/L

1.8L NT engine

2.0L NT engine

2.0L Turbo engine

Compression ratio

9.0:1

9.0:1

7.8:1

Standard compression

185 psi

192 psi

164 psi

Service limit

131 psi

145 psi

121 psi

2G (95-99) T/E

2.0L NT 420A engine

2.0L 4G63 Turbo engine

2.4L NT Spyder engine

Compression ratio

9.6:1

8.5:1

9.5:1

Standard compression

170-225 psi

178 psi

192 psi

Service limit

100 psi

133 psi

146 psi

Galant (89-93)

SOHC 8v engine

SOHC 16v engine

Compression ratio

8.5:1

9.5:1

Standard compression

178 psi

185 psi

Service limit

125 psi

139 psi

Galant (89-93)

DOHC pre-91 NT engine

DOHC 92+ NT engine

DOHC Turbo engine

Compression ratio

9.0:1

9.8:1

7.8:1

Standard compression

192  psi

220 psi

164 psi

Service limit

137 psi

159 psi

114 psi

10. In this picture you might not be able to make out the number ... but ... cylinder 2 is losing compression big-time!

11. Add one capful (1-2 tablespoons) of oil to the cylinder with low compression.

12. Let it sit for a minute to allow the oil to flow down and coat the sides of the cylinder and piston. If there are any gaps in the rings, the oil will seal them for the next few minutes.

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13. Crank the engine for 4 revs, remembering to floor the throttle.

14. If the reading improved significantly (more than 30 psi), your rings are probably worn.

15. If there is little or no improvement, take it to a garage that can perform a leak-down test to determine where the compression is escaping (intake, exhaust, crankcase, gasket, etc.).

16. Replace the plugs, preferably in the same cylinders they came out of. You may want to clean or re-gap them first, or put in new ones. A dab of anti-seize on the threads would be a good idea.

17. Remember to put the MPI fuse and coil connector back. You’re not going anywhere without them!