F 350 4WD Pickup V8-351 5.8L VIN H EFI (1997)
Compression Check: Testing and Inspection
Interpreting Compression Readings
COMPRESSION READINGS
It is recommended the Compression Pressure Limit Chart be used when checking cylinder compression so that the lowest reading number is 75
percent of the highest reading. See: Test Results
If one or more cylinders reads low, squirt approximately one 1.5 ml (1 tablespoon) of SAE 50 weight or equivalent engine oil 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 at fault.
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, cause could be a cylinder
head gasket leak between cylinders. Engine oil or coolant in cylinders can result from this problem.
EXAMPLE READINGS
For example, check the compression pressures in all cylinders. If 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 considered satisfactory.
