Compression Check: Testing and Inspection

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

To check compression use the following procedure:

1. Be sure battery is charged to specifications.
2. Clean the engine, especially the area around the injectors.
3. Warm up the engine by operating for a minimum of 30 minutes at 1200 rpm.
4. Stop the engine and remove the high pressure fuel lines and fuel leak-off line from the engine. Cap all of the openings in the fuel system and fuel injection pump.

NOTE: The line should not be capped until the residual fuel has been removed from them. Otherwise, when the engine is cranked during the compression test the fuel remaining in the lines will blow the caps off.

CAUTION: Do not crank the engine to remove stuck injectors. If an injector is stuck in the head and will not pull straight out, first soak the injector with penetrating fluid for three minutes. Strike the side of the injector body with a brass drift to loosen. If the injector still won't come out, use Injector Removal Tool Kit 014-00269 or Injector Remover Adapter 014-00287 and Slide Hammer T58T-101-A or equivalents. If the injector is allowed to turn in the head, damage to the head will occur, resulting in the need to replace the cylinder head.

5. Remove the injector and seat washer from each cylinder. Cap the injector and line to prevent the entry of dirt into the system. Place the injectors in a rack to protect them from being damaged while they are removed from the engine and to keep them in order.
6. Disconnect the electrical harness to the fuel shutoff solenoid. This must be done to shut off the flow of fuel to the engine during cranking.

VE Pump Solenoid Location:

Injector Pump Solenoid/Connector:

7. Crank the engine to blow out any loose carbon particles from the injector bores.
8. Install the Diesel Engine Pressure Test Adapter kit or 014-00742 or equivalent into the bore of cylinder No.1 using a new seat washer and the injector mounting studs and nuts.
9. Connect the Diesel Engine Compression Test kit 014-00701 or equivalent and hose to the adapter.
10. Crank the engine (speed must be at least 250 rpm) and observe the gauge reading. Allow about 6-8 "puffs" per cylinder.
11. Repeat Steps 7-10 for each cylinder.
12. After completing the compression check, reinstall the injectors (use new washers) and lines and connect the plug to the fuel shutoff solenoid.

Test Conclusions

1. Compression test results are very sensitive to cranking speeds. Compression from cylinder to cylinder must be within 100 psi of each other.
2. lf any of the readings do not meet the above specifications, this indicates that there is a possible leak at the cylinder head gasket, piston rings or valves.

NOTE: To determine if the rings or valves are at fault, squirt the equivalent of a tablespoon of heavy oil into the combustion chamber, then crank the engine to distribute the oil and repeat the compression test. The oil will temporarily seal leakage past the rings. If approximately the same reading is obtained, the rings are satisfactory, but the valves are leaking. If the compression has increased over the original reading, there is leakage past the rings. During a compression test, if the pressure fails to climb steadily and remains the same during the first two succeeding strokes, or fails to climb during the entire test, suspect a sticking valve.

3. A low, even compression in two adjacent cylinders indicates a cylinder head gasket leak. Check head gasket area before rejecting the rings or valves.