## How to Check Back Compression on a Car Engine
What is Back Compression?
Back compression refers to the pressure that builds up in the combustion chamber when the piston moves back up the cylinder after the power stroke. This pressure is a result of the exhaust valve not closing properly, allowing combustion gases to leak back into the cylinder.
Why is Checking Back Compression Important?
Checking back compression is important because it can help identify several issues with your car’s engine, including:
* Worn or damaged exhaust valves
* Leaky valve seals
* Incorrect valve timing
* Damaged piston rings
Symptoms of Back Compression
Common symptoms of back compression include:
* Loss of engine power
* Engine misfires
* Poor fuel economy
* Blue or black smoke from the exhaust
* Rough idle
How to Check Back Compression
To check back compression, you will need the following tools:
* Compression tester
* Screwdriver
* Socket wrench
**Step 1: Safety First**
Disconnect the battery to prevent electrical shock. Allow the engine to cool down thoroughly before beginning any work.
**Step 2: Remove the Spark Plugs**
Use a socket wrench to remove all the spark plugs from the engine.
**Step 3: Disable Fuel System**
Disconnect the fuel pump or pull the fuel pump fuse to disable the fuel system.
**Step 4: Connect the Compression Tester**
Screw the compression tester into the spark plug hole of one of the cylinders. Tighten it securely.
**Step 5: Crank the Engine**
Have a helper crank the engine for about 5-7 seconds. Watch the pressure gauge on the compression tester.
**Step 6: Release the Pressure**
Once the pressure reaches its peak, release it by pressing the button on the compression tester.
**Step 7: Record the Reading**
Record the maximum pressure reading (in psi) obtained for that cylinder.
**Step 8: Repeat for Other Cylinders**
Repeat steps 4-7 for each cylinder to obtain readings for all cylinders.
Interpreting the Back Compression Readings
Compare the back compression readings with the manufacturer’s specifications for your vehicle. Excessive back compression (usually above 10-15 psi) in one or more cylinders indicates a potential problem.
Possible Causes of Back Compression
If you find excessive back compression, it could be due to:
* **Worn or damaged exhaust valves:** Leaking or burned exhaust valves allow combustion gases to escape into the cylinder.
* **Leaky valve seals:** Worn valve seals can lead to poor sealing and allow gases to leak past the valve.
* **Incorrect valve timing:** Misaligned timing can cause the exhaust valve to open prematurely, resulting in back compression.
* **Damaged piston rings:** Broken or worn piston rings can allow combustion gases to seep into the crankcase.
Troubleshooting and Repair
Once you have identified the possible cause of the back compression, the next step is to troubleshoot and repair the issue. This may involve:
* Replacing worn or damaged exhaust valves
* Installing new valve seals
* Adjusting valve timing
* Replacing or repairing piston rings
Conclusion
Checking back compression is an important part of diagnosing engine problems. By following these steps, you can help identify potential issues and ensure your car’s engine is running at its best.
