Jeep Wagoneer/Commando/Cherokee 1957-1983 Repair Information

Checking Engine Compression


See Figure 1

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A noticeable lack of engine power, excessive oil consumption and/or poor fuel mileage measured over an extended period are all indicators of internal engine war. Worn piston rings, scored or worn cylinder bores, blown head gaskets, sticking or burnt valves and worn valve seats are all possible culprits here. A check of each cylinder's compression will help you locate the problems.

As mentioned in the Tools and Equipment section of Chapter 1, a screw-in type compression gauge is more accurate that the type you simply hold against the spark plug hole, although it takes slightly longer to use. It's worth it to obtain a more accurate reading. Follow the procedures below for gasoline and diesel engined trucks.


  1. Warm up the engine to normal operating temperature.
  3. Remove all spark plugs.
  5. Disconnect the high tension lead from the ignition coil.
  7. On fully open the throttle either by operating the carburetor throttle linkage by hand or by having an assistant floor the accelerator pedal.
  9. Screw the compression gauge into the no. 1 spark plug hole until the fitting is snug.


  1. Ask an assistant to depress the accelerator pedal fully on both carbureted and fuel injected trucks. Then, while you read the compression gauge, ask the assistant to crank the engine two or three times in short bursts using the ignition switch.
  3. Read the compression gauge at the end of each series of cranks, and record the highest of these readings. Repeat this procedure for each of the engine's cylinders. Compare the highest reading of each cylinder to the compression pressure specification in the Tune-Up Specifications chart in Tune-up and Performance Maintenance . The specs in this chart are maximum values.

A cylinder's compression pressure is usually acceptable if it is not less than 80% of maximum. The difference between each cylinder should be no more than 12-14 pounds.
