Compression Test

AllData Editors Note - Ford does not provide a cranking pressure specification, only an acceptable range.

COMPRESSION GAUGE CHECK
1. Make sure oil in crankcase is of the correct viscosity and at proper level and battery, is properly charged. Operate vehicle until engine is at normal operating temperature. Turn ignition switch to the OFF position and remove all spark plugs.

2. Install a compression gauge such as Rotunda Compression Tester 164-R0250 or equivalent in No. 1 cylinder.

3. Install auxiliary starter switch in starting circuit. With ignition switch OFF, and using auxiliary starter switch, crank engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.

4. Repeat test on each cylinder, cranking the engine approximately the same number of compression strokes.








TEST RESULTS
The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading.

If one or more cylinders reads low, squirt approximately one tablespoon of clean engine oil meeting Ford specification ESE-M2C153-E on top of the pistons in the low-reading cylinders. Repeat compression pressure check on these cylinders.

COMPRESSION READINGS-INTERPRETING
1. If compression improves considerably, piston rings are damaged.
2. If compression does not improve, valves are sticking or seating poorly.
3. If two adjacent cylinders indicate low compression pressures and squirting oil on pistons does not increase compression, the head gasket may be leaking.between cylinders. Engine oil/coolant in cylinders could result.

EXAMPLE READINGS
If, after checking the compression pressures in all cylinders, the highest reading was 1351 kPa (196 psi) and the lowest pressure reading was 1069 kPa (155 psi), the engine is within specification and the compression is satisfactory.