How to Fix Low Engine Compression

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Any type of engine needs compression to work properly. If your vehicle has a low compression problem it can cause a lot of headaches and, possibly, wallet aches. In this article we will explain how to fix low compression in an engine.

7 Reasons for Low Engine Compression

There are a variety of causes for low engine compression. These are some of the most common problems that can result in reduced engine compression:

1. Damaged Pistons

An overheated engine can cause holes to form in the pistons. While the pistons are made from a strong aluminum alloy, they will degrade over time. Hot spots will eventually wear holes in the pistons, and the holes might allow gas to escape into the combustion chamber and result in low compression.

2. Valve Leaks

As you might expect, valve leaks can also lead to low compression as gas can escape through damaged seals and other faults in the valves. Each cylinder has two valves, an intake and exhaust. These valves may be damaged by overheating or they can just wear out over time.

Also Read: How to Test a Gas Cap for Leaks

3. Worn Out Timing Belt

If your timing belt is worn out, the camshaft may not be able to turn. Since the camshaft connects to the exhaust and intake valves on the cylinders, if the camshaft is unable to turn, the necessary compression levels can’t form within the engine.

4. Blown Head Gasket

A blown head gasket can result in reduced compression by causing a gap to form between the cylinder and the head. This gap can allow gas to escape from the cylinder, which will result in lowered compression.

5. Faulty Piston Rings

The piston rings form a seal between the cylinder wall and the piston. As previously mentioned, a lack of a seal can allow gas to escape and lead to low compression. There are three rings that create the seal for each piston. Like the other parts on this list, the rings wear out over time or become damaged due to overheating. You may need to replace all the rings at once as they should degrade at the same time.

6. Broken Camshaft

Similar to a worn out timing belt, a broken camshaft will make it so the engine can’t get the required compression levels to be able to run. This is because a broken camshaft will cause the crankshaft to fail, which will, in turn, prevent the pistons from moving as they should. Although a broken camshaft doesn’t happen often, it is still worthwhile to check if you are experiencing low compression in your vehicle’s engine.

Also Read: What Happens When a Camshaft Sensor Fails

7. Faulty Camshaft Lobe

Also known as a flattened camshaft lobe, this problem can also prevent a good seal and result in low engine compression. The lobes help open and close the cylinder valves. If the lobes get stuck they can prevent the valves from opening or closing. If the valve and lobe get stuck open, this will cause low engine compression.

4 Signs of Low Engine Compression

How will you know to look for problems that can cause low engine compression? There are a few signs you need to look out for that will tell you if you are experiencing this issue.

1. Engine Misfire

If your vehicle is misfiring, this can be a sign of reduced compression in one of the cylinders. Engine misfires happen when your engine misses a step of the combustion cycle. Compression being one of these steps, if it is missed or not executed properly, you may experience a misfire.

Also Read: How Long Can I Drive With a Misfiring Cylinder

2. Power Loss

If you aren’t able to get your vehicle up inclines at a normal speed, you may be experiencing a loss of power. Problems with some of the cylinders, such as low compression, can cause power losses. For example, if two out of four cylinders aren’t working properly, this will result in an equivalent loss of power of about fifty percent. You can still drive your vehicle in this state, but if you aren’t able to navigate hills or other inclines, it can be dangerous.

3. Faster Loss of Fuel

You may notice a reduction in the fuel efficiency of your vehicle. If your fuel economy is being affected, it could be because of a lack of compression. Higher compression means better fuel efficiency, so if you have low engine compression the fuel economy will suffer. You can check your fuel efficiency by watching how much fuel is used for a specific number of miles. If you’re using up more fuel than you normally would on your commute, for example, it may be a sign of low engine compression.

4. Engine Not Starting

If all of your vehicle’s cylinders fail, you will not be able to start your engine at all. If the failure of your cylinders is caused by low compression, the cylinders won’t be able to ignite the fuel-air mixture, so the engine can’t start. This can be especially concerning as there are several problems that can cause the engine to fail to start that can be very expensive to fix.

How to Correct Low Engine Compression

Thankfully, you can fix low engine compression without too much difficulty. You will need a compression gauge and tools to access, remove, and replace parts on the vehicle’s engine. Below is a step-by-step guide on how to do it:

1. Confirm that the compression in the engine is low.

The first step is obviously to ensure that the cause of your problems is, in fact, low compression. You can do this by using a compression gauge to run a compression test.

To perform a compression test, first remove the fuel-injection fuses and the fuel pump. Then disconnect the main wire connected to the coil and the spark plug wires. Finally, take out the spark plugs.

Second, screw the compression gauge’s threaded end into a spark plug hole. You will then turn on the ignition. Depress the throttle. Then, crank the engine to four revolutions, or up to ten if the reading is not stable.

Using chalk, make note of the reading on the pressure gauge on the valve cover. Move to the next cylinder and repeat the above process. If you had to crank up to ten revolutions on the first cylinder, make sure to do so on the remaining cylinders to ensure an accurate compression test.

The ideal compression is more than one hundred pounds per square inch, per cylinder. There should be no more than a ten percent difference between the lowest and highest readings.

2. Determine the cause and repair or replace it.

Once you have tested your engine compression and found low compression, you will have to figure out what is causing the low compression. Unfortunately, the only true way to stop low compression is to replace the failing part or parts, so fixing this issue can be costly. Because there may be more than one part that is causing the compression problems, be sure to methodically go through the possible faulty parts.

Once you find a problem part, replace it and run another compression test to see if the replacement solved the issue. If it doesn’t, continue searching for damaged parts and replacing them until your compression test runs normal.

You may be able to repair a faulty part using a compression repair product. However, this solution should not be used instead of replacing a faulty part simply to save money. The repair job won’t last forever, and it will be easier and cost less time to just replace the part now.

3. Test drive your car

Once your compression test results return to normal, take your vehicle for a test drive. While on the test drive, make sure to keep an eye out for further symptoms of low compression as listed previously in this article. If you continue to experience problems, you will have to repeat the previous steps as you may have missed a faulty or damaged part.

Your vehicle should run without misfiring, the engine should start up like normal, there should be no loss of power, and your fuel efficiency should be normal. Make sure to watch for each of these possible issues even if they weren’t occurring originally as a new symptom may have popped up since you made your repairs. If there are no further problems, you will have fixed your low compression problem.

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Low compression in your vehicle’s engine can cause a lot of problems. It can also be costly to repair as you will need to replace whatever part or parts are preventing proper compression in the engine. Thankfully, it is not difficult to test for compression issues at home.

By following this step-by-step guide, you will have learned how to identify, diagnose, and repair low compression in your engine. To learn more about common vehicle and engine problems, as well as how to fix them, explore our other articles.

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