Compression Test - Interpreting Compression Readings
WARNING: This page is about a different car, the 2005 Ford RV Cutaway, 2005 Ford Econoline, 2005 Ford E450 Super Duty, and 2005 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
- If compression improves considerably, piston rings are faulty.
- If compression does not improve, valves are sticking or seating incorrectly.
- If two adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression (GASOLINE ENGINES ONLY), the head gasket may be leaking between cylinders. Engine oil 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.