Pressure, Vacuum and Temperature Specifications

NOTE:
^ The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.
^ Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the indicated compression pressures may not be valid for diagnosis purposes.

CAUTION: DO NOT overspeed the engine.

a. Check engine oil level and add oil, if necessary.
b. Drive the vehicle until engine reaches normal operating temperature.
c. Select a route free from traffic and other forms of congestion, observe all traffic laws and briskly accelerate through the gears several times. The higher engine speed may help clean out valve seat deposits which can prevent accurate compression readings.
d. Remove all spark plugs from engine. As spark plugs are being removed, check electrodes for abnormal firing indicators-fouled, hot, oily, etc. Record cylinder number of spark plug for future reference.
e. Disconnect coil wire from distributor and secure to good ground to prevent a spark from starting a fire.
f. Be sure throttle blades are fully open during the compression check.
g. Insert compression gauge adapter into the No. 1 spark plug hole. Crank engine until maximum pressure is reached on gauge. Record this pressure as No.1 cylinder pressure.
h. Repeat above step for all remaining cylinders.
i. Compression should not be less than 689 kPa (100 psi) and not vary more than 172 kPa (25 psi) from cylinder to cylinder.
j. If cylinder(s) have abnormally low compression pressures, repeat procedure.
k. If the same cylinder(s) repeat an abnormally low reading, it could indicate the existence of a problem in the cylinder.

NOTE: The recommended compression pressures are to be used only as a guide to diagnosing engine problems. An engine should NOT be disassembled to determine the cause of low compression unless some malfunction is present.