Diesel compression testing

deDiesel compression testing

When it comes to diesel engines, it is extremely important to have your vehicle running in top shape.テつ Diesel engines do not use spark plugs like the gasoline brothers; instead they use glow plugs and compression to spark the air fuel mixture.テつ The glow plugs are used only until the engine is warmed up to operating temperature, then the engines compression is the only thing causing the air fuel mixture to burn.テつ This happens by an extremely high compression rate, causing the air and fuel to detonate, such as they would in a car with high compression running a low octane fuel, except in this case it is wanted.テつ This detonation is what starts the power stroke in the diesel engine. テつテつ

Due to the high compression ratios of diesel engines, it is a slightly different procedure for testing the vehicles compression.テつ You will not be able to use a gasoline engine compression tester because the diesel engine puts out more compression and will either destroy or not read on the gasoline engine tester.テつ There are two different methods for testing compression on diesel engines, and both will work well.テつ It just depends on your application.テつ We will discuss both of these methods.

The Procedure

Glow Plug Method

  1. First you are going to want to make sure that your vehicle is parked in a location where it can sit for awhile.
  2. Next you are going to want to locate and remove your glow plugs on your engine.テつ If you are unsure where they are located, consult the service manual.
  3. With the glow plugs removed on every cylinder you are going to want to crank the engine over 5 times or so to clear out the compression.
  4. While you are doing testing you are going to want to connect a battery charger to your battery to prevent the battery from draining while cranking.テつ This SOLAR 12volt Automatic on off Charger will work to keep the battery charging.
  5. With the battery charger connected you are ready to connect your compression tester.テつ I recommend using this ATD5560 Diesel Compression Tester and along with this you are going to need a glow plug adapter like this ATD5673 Glow Plug Adapter.テつ For more adapters visit Tooldesk.
  6. Thread in the ATD5673 Glow Plug Adapter into one of the glow plug holes.テつ Then connect the ATD5560 Diesel Compression Tester.テつ Now you are going to want to hold the throttle wide open, and crank the engine for 5 revolutions.テつ Record the reading on your gauge.テつ Then relieve the pressure by using the release valve.
  7. After recording the cylinder and the compression from that cylinder you are ready to move onto the next cylinders.テつ Do the same thing and repeat step 6 for every cylinder.テつ Make sure to keep the cylinders on a piece of paper and record the proper compression for each one.
  8. Once you have completed all of the cylinders and have all of the compressions listed you are ready to see the results of your testing.テつ Take your lowest number and highest number, and they should be within 25% of each other as a rule of thumb.テつ If they are then your cylinders are in good condition.テつ If not, then any cylinder that is lower than 25% of the highest is considered low and may need to be looked at for further repair.

This is the procedure for testing using the glow plug method.テつ This method is the most common method of testing, but some people prefer to use the injectors as a point of testing.テつ This is because they feel that some compression can leak past the injectors causing incorrect readings.テつ If you want to be 100% sure and want to spend the extra money on the adapter or do this for a living then I would recommend checking each cylinder using the injectors.

The Injector Method

  1. You again are going to want to make sure your vehicle is parked somewhere that it can sit for a couple hours.
  2. Next you are going to want to disable the fuel pump.テつ This will prevent any fuel from leaving through the removed injectors.
  3. Again you are going to want to connect a battery charger to the engine.
  4. Then crank the engine over five times with all of the injectors removed, clearing all of テつthe compression out of the cylinders.
  5. You will now need to buy the proper injector connector for the ATD5560 Diesel Compression Tester.テつ This ATD5672 Detroit Injector Adapter will work for Detroit diesel engines.テつ If you want to find the proper adapter visit Tooldesk.
  6. With the ATD5560 Diesel Compression Tester connected to the proper injector adapter you are ready to crank the engine over.テつ Again hold the throttle wide open and crank the engine over 5 times.テつ Record the compression from the gauge and the cylinder on a sheet of paper.テつテつ Then relieve the pressure.
  7. Move onto the next cylinder and repeat step 6.テつ Do so for every cylinder making sure to record the number of the cylinder and the compression of that cylinder.
  8. When you are done testing every cylinder replace the injectors, and the fuse for the fuel pump.
  9. Check your readings; again every reading should be within 25% of each other.テつ If they are not, then the cylinders that are low may need to be serviced.

You just finished checking your diesel engines compression.テつ Whatever method you choose will be accurate.テつ Just make sure to take your time and record your readings.

Written by: Cody Mammenga an NDSCS Student

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