1. Engine Compression Testing
R. Bortignon

2. Engine Condition Analysis – Compression Testing
A compression test tells us what the physical condition of the engine is…
1. Remove all the spark plugs
2. Disable the ignition system (yellow arrows)
(unhook negative side of the coil)
Ignition Coils

3. 3. screw a threaded adapter into one of the spark plug holes
4. crank the engine through 5 compression strokes
5. record your reading and repeat #1 thru #4 on the remaining cylinders
Pressure
Gauge
Adapter
Coupler
Various
Threaded
Adapters

4. 4 5 3 2 1

5. Interpreting the Readings
Check “Mitchell” for the compression specifications of your vehicle (in the engine performance section)
Low compression is usually the result of a leaking valve

6. Burnt valves
can be caused by insufficient valve clearance

7. worn compression rings and/or cylinder walls…

8. Interpreting the Readings
or a blown cylinder head gasket…

9. Diagnosing Low Compression Readings
Engine Spec’s: 150 PSI +/- 10%
Cylinder #1: 150 PSI
Cylinder #2: 160 PSI
Cylinder #3: 70 PSI
Cylinder #4: 150 PSI
Probable Cause: Leaking valve

10. Engine Spec’s: 140 PSI +/- 10%
Cylinder #1: 90 PSI
Cylinder #2: 105 PSI
Cylinder #3: 100 PSI
Cylinder #4: 105 PSI
Probable cause: worn rings and cylinders

11. Engine Spec’s: 160 PSI +/- 10%
Cylinder #1: 20 PSI
Cylinder #2: 20 PSI
Cylinder #3: 150 PSI
Cylinder #4: 140 PSI
Probable cause: blown head gasket

12. Engine Spec’s: 150 PSI +/- 10%
Cylinder #1: 190 PSI
Cylinder #2: 210 PSI
Cylinder #3: 200 PSI
Cylinder #4: 195 PSI
Probable cause: excessive carbon build-up