Interpreting Compression Readings

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

Compression Pressure Limits:

The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading. Refer to the Compression Pressure Limit Chart.

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 the compression pressure check on these cylinders.

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