Interpreting Compression Readings

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

1. If compression improves considerably, piston rings are faulty.
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 piston does not increase compression, the head gasket may be leaking between cylinders. Engine oil and/or coolant in cylinders could result from this condition.

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


Example: If, after checking the compression pressures in all cylinders, the highest reading obtained 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.