Interpreting Compression Readings

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

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

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, a head gasket may be leaking between cylinders. Engine oil and/or coolant in cylinders could result.

Use the Compression Pressure Limit Chart when checking cylinder compression so that the lowest reading number is 75 percent of the highest reading.

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 considered satisfactory.