Poorly performing engines that lose power, especially when traversing an incline, are often the result of low compression in one or more cylinders. Internal combustion engines operate off a controlled explosion of a compressed air-fuel mixture inside the cylinders. When the cylinders become worn they are not able to effectively contain the expanding gas. To determine if power loss is the result of bad compression rings or valves, perform a compression to diagnose a bad cylinder.
Call a dealership's service department or search online to obtain the cylinder compression figures for your vehicle's engine.
Disconnect the hot (red) wire from the fuel injector system with a screwdriver. If the engine is carbureted, rather than fuel injected, rotate the throttle linkage on the carburetor all the way back and stick a wrench or screwdriver in the throttle linkage to block the throttle all the way open.
Pull the coil wire off the distributor; the coil wire is the middle wire on the distributor cap.
Pull the wire off the spark plug nearest the front of the engine. If the engine is oriented sideways begin with the spark plug closest to the driver's side door. Remove the spark plug from the socket with a spark plug wrench.
Twist the threaded insert of the compression gauge into the empty spark plug socket with your fingers. Tighten the insert in place with a box end wrench.
Tie a piece of string around the neck of the compression gauge. Secure the string to a convenient spot, such as around the lip of the empty socket where the coil wire was removed from the distributor.
Place the vehicle's gearshift in "park." Crank the engine over, continually, six times. Read the numbers on the dial of the compression gauge. Cylinder compression is generally consider acceptable if the reading is at least 80 percent of the maximum PSI reading listed for your vehicle's engine.
Remove the compression gauge. Stick the tip of a screwdriver into a bottle of motor oil and shake four drops of motor oil into the cylinder through the spark plug hole with the tip of the screwdriver.
Replace the compression gauge and repeat the test. If the compression reading increases after adding oil to the cylinder the compression rings are worn and will need repair to bring compression into the normal range. If the compression does not increase the problem is a worn valve or a bad head gasket, which will necessitate removal of the head.
Repeat the test on each of the remainder of the cylinders.
