Compression Check

TOOLS REQUIRED:  SA9127E Gauge Bar Set

If there is lack of power, excessive oil consumption, or poor fuel economy, etc., measure the compression pressure.

1. Start the engine and allow it to reach normal operating temperature.
2. Shut engine off and disconnect the ignition module connector.
   Fig 1: Ignition Module Connector

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3. Disconnect spark plug wires and remove all four spark plugs.
4. Insert a compression Gauge Bar Set SA9127E into the spark plug hole.
5. Fully open throttle.
   Fig 2: Cylinder Pressure Specifications

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   NOTE: Always use a fully charged battery to obtain engine revolutions of 250 RPM minimum. Do not crank the engine for more than 15 seconds.
6. While cranking engine, measure compression. The cylinder should puff or compression gauge needle should bounce a minimum of 10 times.
   NOTE: All measurements must be completed in as short a time as possible. Check low cylinders and make sure a minimum of 10 puffs are obtained prior to reading the gauge.
7. Repeat the previous steps for each cylinder.
   NOTE: No compression in two or more cylinders is an indication of damaged timing chain sprockets, camshaft(s), crankshaft key or pins.

   SPECIFICATIONS 

   1. Normal Compression Pressure: 1276-1344 kPa (185-205 psi) 
   2. Minimum Compression Pressure: 1241 kPa (180 psi) 
   Fig 3: Measuring Compression

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   • Normal Compression: Builds up quickly and evenly to specification in each cylinder.
   • Low Compression: Damaged piston, ring(s), valve(s), or head gasket.
   • High Compression: Carbon on pistons/combustion chamber.
     Fig 4: Engine

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     NOTE: A cylinder leakage test can be performed to further determine location of compression leakage if one or more cylinders are extremely low.
8. If the cylinder compression in one or more cylinders is low, pour a small amount (one teaspoon) of engine oil into the cylinder through the spark plug hole.
   Fig 5: Spark Plug Hole Location

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9. Place a shop towel over plug holes to capture any oil mist/spray.
   Fig 6: Covering Spark Plug Holes

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10. Crank the engine over for a few seconds without the compression gauge or spark plugs installed.
11. Repeat previous steps  4- 7 to measure compression.
12. If adding oil increases compression readings:
    • Pistons Rings Leaking: Compression low on first stroke (first gauge puff) and tends to build up on following strokes, but does not reach normal compression pressure. Improves considerably with oil. Inspect for worn or broken ring(s) and piston ring land wear (pound out).
      Fig 7: Inspecting For Worn Or Broken Piston Rings

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13. If adding oil does not increase compression:
    • Valves or Head Gasket Leaking: Compression low on first stroke. Does not tend to build up on following strokes. Does not improve with adding oil to cylinder.
      Fig 8: Checking Valve Or Head Gaskets

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    • Head Gasket: Two adjacent cylinders have lower than normal compression and adding oil to the cylinder does not improve compression.
      Fig 9: Checking Head Gasket

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14. Remove compression tester and install spark plugs.

    Torque: 

    Spark Plug-to-Head: 27 N.m (20 ft. lbs.) 

15. Connect spark plug wires. Make sure spark plug boots are firmly seated.
16. Connect ignition module connector.
    Fig 10: Installing Spark Plugs And Connecting Ignition Module

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17. Release throttle if previously set fully open.