Interpreting Compression Readings

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

1. If compression improves considerably, the piston rings are faulty.
2. If compression does not improve, the valves are sticking or seating improperly.
3. If two adjacent cylinders indicate low compression pressures and squirting oil on the 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 is within 75 percent of the highest reading.