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Compression Test 3.0L

  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.
  2. Turn the ignition switch to the OFF position, then remove all the spark plugs. REFER to: Spark Plugs .
    GFD510358Courtesy of FORD MOTOR COMPANY
  3. Loosen the clamps, then remove the charge air cooler outlet pipe.
    GFD510359Courtesy of FORD MOTOR COMPANY
  4. Manually set the throttle plates to the wide-open position.
  5. Install a compression gauge in the No. 1 cylinder.
  6. 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.
  7. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
  8. Install all the spark plugs. REFER to: Spark Plugs .
    GFD510358Courtesy of FORD MOTOR COMPANY
  9. Install the charge air cooler outlet pipe.

Compression Test 3.3L 

  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.
  2. Turn the ignition switch to the OFF position, then remove all the spark plugs. Refer to the appropriate Engine article for the procedure.
    GFD510360Courtesy of FORD MOTOR COMPANY
  3. Loosen the clamp and position the air cleaner outlet pipe aside.
    GFD510361Courtesy of FORD MOTOR COMPANY
    1. Detach the degas bottle hose and position aside.
    2. Disconnect the quick release coupling and position aside the crankcase ventilation tube. REFER to: Quick Release Coupling (310-00 Fuel System - General Information).
    3. Disconnect the quick release coupling and position aside the atmospheric tube. REFER to: Quick Release Coupling (310-00 Fuel System - General Information).
    4. Detach the clip and position aside the vacuum tube.
    GFD510362Courtesy of FORD MOTOR COMPANY
  5. Loosen the clamp and remove the air cleaner outlet pipe.
    GFD510363Courtesy of FORD MOTOR COMPANY
  6. Manually set the throttle plates to the wide-open position.
  7. Install a compression gauge in the No. 1 cylinder.
  8. 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.
  9. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
  10. Install all the spark plugs. Refer to the appropriate Engine article for the procedure.
    GFD510362Courtesy of FORD MOTOR COMPANY
  11. Install the air cleaner outlet pipe and tighten the clamp.
    GFD510361Courtesy of FORD MOTOR COMPANY
    1. Connect the degas bottle hose.
    2. Install the crankcase ventilation tube. REFER to: Quick Release Coupling (310-00 Fuel System - General Information).
    3. Connect the atmospheric tube. REFER to: Quick Release Coupling (310-00 Fuel System - General Information).
    4. Attach the vacuum tube.
    GFD510360Courtesy of FORD MOTOR COMPANY
  13. Install the air cleaner outlet pipe and tighten the clamp.

Compression Test - Hybrid 

The compression test requires cranking the engine a minimum of 5 compression strokes with the throttle plate in the wide-open position for each cylinder. The engine cranking diagnostic mode must be used to crank the engine and the brake/accelerator pedals must be used to position the throttle plate during the compression test. The engine cranking diagnostic mode is a PCM strategy which is separate from the normal operating strategy. It allows the engine to crank in a similar fashion as a conventional vehicle with the fuel disabled. When in this mode, the PCM commands the TCMto spin the generator, which cranks the engine with the speed between 900 and 1, 200 rpm. The engine will crank as long as the traction battery state of charge stays greater than 35%.

  1. Make sure the oil in the crankcase is of the correct viscosity and at the correct level. Operate the vehicle until the engine is at normal operating temperature.
  2. Using the VCM, access the BCM - HVTB (high voltage traction battery) and monitor the traction battery state of charge PID. If the monitored PID displays the state of charge below 45%, start and idle the engine with full A/C ON. When the traction battery state of charge exceeds 45%, the engine cranking diagnostic mode can be activated.
  3. NOTE: All spark plugs must be removed to check compression. Failure to remove all spark plugs can result in inaccurate test results.

    Turn the ignition switch to the OFF position. Then remove all the spark plugs.

  4. Install a compression gauge such as the Quick Disconnect Compression Tester in the No. 1 cylinder.
  5. Press the brake and accelerator pedal fully.
  6. Press the start button to crank the engine or turn the key for vehicles with key start to start the vehicle.
  7. The engine will crank for approximately 3 seconds. Release the accelerator pedal.
  8. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
  9. Position the key to the OFF position to deactivate the cranking diagnostic mode.
  10. Clear all DTC.

Compression Test - Test Results 

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

Compression Pressure Limit Chart 

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

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.

Compression Test - Interpreting Compression Readings 

  1. If compression improves considerably, piston rings are worn or damaged.
  2. If compression does not improve, valves are sticking or not seating correctly.
  3. 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.
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