Check Compression on a First Generation Mitsubishi Eclipse

Checking the engine's compression allows you as the individual to identify if the motor is in some kind of mechanical problem. It makes sure the engine is up to factory specs and is working efficiently.

Steps

  1. Gather the tools required to complete the compression test. You will need a ratchet, spark plug socket, and a compression tester which you can easily rent from any auto parts store. You will also need some sort of repair manual, Haynes, Etc.
  2. Once all tools are gathered, find a place in which you would be performing the compression test, driveway, garage, etc. As well as the vehicle in which you would be doing the test on. Once you obtain the place and all the tools, and the vehicle, let the vehicle get up to operational temperature. NOTE: You do not want to do a compression test on a cold engine, metal expands when hot and allows everything to fully operate. This way all the parts expand on heat and keep a better compression.
  3. Once vehicle has reached operational temperature shut the engine off, and open up the hood of the car, Use caution as to motor will be warm and certain components could burn skin on contact, Such as exhaust manifold. Once the hood of the car is open locate the spark plugs. There will be four of them since this is a 4 cylinder motor, and all four of them will be sitting on top of the vale cover
  4. Remove all of the spark plugs from the engine
  5. Disconnect the primary wires from the distributor and make sure the main harness coming from the distributor is disconnected from the motor. NOTE- Doing this will eliminate shock when doing test!
  6. Install the compression gauge in the number one spark plug hole. Make sure the gauge can rest somewhere safe where it will not fall while you are cranking the car.
  7. Crank the engine over at least six compression strokes. Make sure you have a (WOT) " throttle should be wide open". You should be able to count how many times the motor tries to turn over. This is known as compression strokes. Once you let it turn over, turn the key off and check the gauge.
  8. Record what the gauge reads and proceed this for each cylinder head/ spark plug hole.
  9. Once finished with all four readings compare the readouts with each cylinder. The readings should be no more or less than 20% of the others. The readings should be anywhere from 155+ across the board, depending on mileage.
  10. If the compression is high, the combustion chambers are probably built up with carbon deposits, if the case, then the cylinder head needs to be removed and de-carbonized
  11. If the compression is lower, or varies greatly between cylinders, perform a leak down test, or have a shop perform one. This will show exactly where leaking is occurring and how bad it is.
  12. Once test is finished, make sure you screw all four spark plugs back in, and hook up the distributor harness back to the engine. Double check everything is plugged back in before you attempt to start the vehicle!

Tips

  • Gathering all tools and manuals will be very helpful before you start.
  • The test can be done with one person, but having another to help might make things easier.

Warnings

  • Do not attempt test if you are not comfortable around engines.
  • Beware of hot parts on the vehicle and know how to work around them
  • Electrical shock will happen if electrical harness is NOT disconnected from distributor

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