Engine Compression Test 5.7L







Charge the battery if the battery is not fully charged



Disable the ignition system



Disable the fuel injection system



Remove all of the spark plugs



Block the throttle plate wide open



Start with the compression gauge at zero, and crank the engine through 4 compression strokes (4 puffs)



Make the compression check for each cylinder. Record the reading



If a cylinder has low compression, inject approximately 15 ml (one tablespoon) of engine oil into the combustion chamber through the spark plug hole


Recheck the compression and record the reading



The minimum in any one cylinder should not be less than 70% of the highest cylinder. No cylinder should read less than 698kPa (100 PSI)


For example, if the highest pressure in any one cylinder is 1035kPa (150 PSI), the lowest allowable pressure foe any other cylinder would be 725kPa (105 PSI).




  • Normal Compression builds up quickly and evenly to the specified compression for each cylinder
  • Piston Rings Leaking Compression is low on the first stroke. Compression builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
  • Valves Leaking Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you ad oil.
  • If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be the head gasket leaking between the cylinders.


Information supplied by Eboggs_jkvl per 1998 Helms Manual Volume 3, 6-252