Lincoln Corsair: Engine System - General Information / General Procedures - Compression and Cylinder Leakage Test

1. Make sure the oil in the crankcase is of the correct viscosity and at the correct level and that the battery is correctly charged. Operate the vehicle until the engine is at normal operating temperature. Turn the ignition switch to the OFF position.
   

1. Remove the spark plugs.
   For additional information, refer to: Spark Plugs (303-07A Engine Ignition - 2.0L EcoBoost (177kW/240PS) – MI4/2.0L EcoBoost (184kW/250PS) – MI4, Removal and Installation).
   For additional information, refer to: Spark Plugs (303-07B Engine Ignition - 2.3L EcoBoost (199kW/270PS), Removal and Installation).
   For additional information, refer to: Spark Plugs (303-07C Engine Ignition - 2.5L Duratec – Hybrid (121kW/164PS) (BG), Removal and Installation).

1. Set the throttle plates in the wide-open position.
   

1. Install a compression gauge in the No. 1 cylinder.
   

1. Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of 5 compression strokes and record the highest reading. Note the approximate number of compression strokes necessary to obtain the highest reading.
   

1. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
   

Compression Test - Test Results

1. The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75% of the highest reading.
   

Compression Pressure Limit Chart

1. Refer to the Compression Pressure Limit Chart.
   

   Maximum Cylinder Pressure - Minimal Cylinder Pressure	Maximum Cylinder Pressure - Minimal Cylinder Pressure	Maximum Cylinder Pressure - Minimal Cylinder Pressure	Maximum Cylinder Pressure - Minimal Cylinder Pressure
   134.0 –100.9  psi ( 924 –696  kPa)	164.0 –123.0  psi ( 1,131 –848  kPa)	194.1 –145.0  psi ( 1,338 –1,000  kPa)	223.9 –168.0  psi ( 1,544 –1,158  kPa)
   136.0 –102.0  psi ( 938 –703  kPa)	166.1 –124.0  psi ( 1,145 –855  kPa)	195.9 –147.1  psi ( 1,351 –1,014  kPa)	226.0 –169.0  psi ( 1,558 –1,165  kPa)
   138.1 –104.0  psi ( 952 –717  kPa)	168.0 –126.0  psi ( 1,158 –869  kPa)	198.0 –147.9  psi ( 1,365 –1,020  kPa)	228.0 –171.0  psi ( 1,572 –1,179  kPa)
   140.0 –105.0  psi ( 965 –724  kPa)	170.0 –127.1  psi ( 1,172 –876  kPa)	200.0 –150.0  psi ( 1,379 –1,034  kPa)	230.0 –172.0  psi ( 1,586 –1,186  kPa)
   142.0 –107.0  psi ( 979 –738  kPa)	172.0 –128.9  psi ( 1,186 –889  kPa)	201.9 –151.0  psi ( 1,392 –1,041  kPa)	232.1 –174.0  psi ( 1,600 –1,200  kPa)
   143.9 –108.1  psi ( 992 –745  kPa)	174.0 –131.0  psi ( 1,200 –903  kPa)	204.1 –153.0  psi ( 1,407 –1,055  kPa)	233.9 –175.1  psi ( 1,613 –1,207  kPa)
   146.1 –109.9  psi ( 1,007 –758  kPa)	176.1 –132.0  psi ( 1,214 –910  kPa)	206.0 –154.0  psi ( 1,420 –1,062  kPa)	236.0 –176.9  psi ( 1,627 –1,220  kPa)
   147.9 –111.0  psi ( 1,020 –765  kPa)	178.0 –133.0  psi ( 1,227 –917  kPa)	208.0 –155.9  psi ( 1,434 –1,075  kPa)	238.0 –178.0  psi ( 1,641 –1,227  kPa)
   150.0 –113.0  psi ( 1,034 –779  kPa)	180.0 –135.0  psi ( 1,241 –931  kPa)	210.0 –157.1  psi ( 1,448 –1,083  kPa)	240.0 –180.0  psi ( 1,655 –1,241  kPa)
   152.0 –114.0  psi ( 1,048 –786  kPa)	182.0 –135.8  psi ( 1,255 –936  kPa)	212.0 –157.9  psi ( 1,462 –1,089  kPa)	242.1 –181.0  psi ( 1,669 –1,248  kPa)
   154.0 –115.0  psi ( 1,062 –793  kPa)	184.1 –138.1  psi ( 1,269 –952  kPa)	214.1 –160.0  psi ( 1,476 –1,103  kPa)	244.0 –183.0  psi ( 1,682 –1,262  kPa)
   156.1 –117.0  psi ( 1,076 –807  kPa)	185.9 –140.0  psi ( 1,282 –965  kPa)	216.0 –162.0  psi ( 1,489 –1,117  kPa)	246.0 –184.1  psi ( 1,696 –1,269  kPa)
   157.9 –118.1  psi ( 1,089 –814  kPa)	188.0 –141.0  psi ( 1,296 –972  kPa)	218.0 –163.0  psi ( 1,503 –1,124  kPa)	248.0 –174.3  psi ( 1,710 –1,202  kPa)
   160.0 –119.9  psi ( 1,103 –827  kPa)	190.0 –142.0  psi ( 1,310 –979  kPa)	220.0 –165.1  psi ( 1,517 –1,138  kPa)	250.0 –187.0  psi ( 1,724 –1,289  kPa)
   161.0 –121.0  psi ( 1,110 –834  kPa)	192.0 –144.0  psi ( 1,324 –993  kPa)	236.6 –166.1  psi ( 1,631 –1,145  kPa)	251.9 –189.0  psi ( 1,737 –1,303  kPa)

Compression Test - Interpreting Compression Readings

1. If one or more cylinders reads low, squirt approximately one tablespoon of engine oil meeting Ford specification on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
   

1. If compression improves considerably, piston rings are worn or damaged.
   

1. If compression does not improve, valves are sticking or not seating correctly.
   

1. If 2 adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression, 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 the lowest reading is within 75% of the highest reading.
   

Cylinder Leakage Test

1. When a cylinder produces a low reading, use of a cylinder leakage tester will be helpful in pinpointing the exact cause.
   

1. The leakage tester is inserted in the spark plug hole, the piston is brought up to TDC on the compression stroke, and compressed air is admitted.
   

1. Once the combustion chamber is pressurized, the leakage tester gauge will read the percentage of leakage. Leakage exceeding 20% is excessive.
   

1. While the air pressure is retained in the cylinder, listen for the hiss of escaping air. A leak at the intake valve will be heard in the TB (throttle body). A leak at the exhaust valve can be heard at the tailpipe. Leakage past the piston rings will be audible at the PCV connection. If air is passing through a blown head gasket to an adjacent cylinder, the noise will be evident at the spark plug hole of the cylinder into which the air is leaking. Cracks in the cylinder block or gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator.
   

1. Install the spark plugs.
   For additional information, refer to: Spark Plugs (303-07A Engine Ignition - 2.0L EcoBoost (177kW/240PS) – MI4/2.0L EcoBoost (184kW/250PS) – MI4, Removal and Installation).
   For additional information, refer to: Spark Plugs (303-07B Engine Ignition - 2.3L EcoBoost (199kW/270PS), Removal and Installation).
   For additional information, refer to: Spark Plugs (303-07C Engine Ignition - 2.5L Duratec – Hybrid (121kW/164PS) (BG), Removal and Installation).