Understanding the PCV System How to Replace PCV valve?

aThe PCV system on modern vehicles plays a major role in the proper operation of the engine.  It is a very simple system and often time is forgotten about in diagnosis.  The PCV or Positive Crankcase Ventilation system if working incorrectly can lead to many problems in driveability.

The PCV system works by allowing fresh air from your intake tubing to blow through the engine.  This clean air then mixes with hydrocarbons and then passes into your intake manifold to be burned.  The PCV system prevents pressure from building up in your engine and is also an emission device.

If you have a PCV system that is not working correctly you can have many problems with your vehicle.  We will discuss some of these problems but first we must understand the components of the PCV system.

  1. The first component is the tube that travels from your intake to the valve cover of your engine.
  2. Next there is a spring loaded valve on your other valve cover generally that allows crankcase pressure to escape.
  3. After the valve there is a tube that runs into your intake manifold.

Now that we understand the parts of the PCV system we can discuss some of the problems that can occur with your PCV system and what they can lead to.

One of the most common problems that can happen to your PCV system is that you can break a line or have a restricted line.  If you have a broken or restricted line this can lead to a vacuum leak or excessive crankcase pressure.  With excessive pressure you can have oil leaks or have oil be blown back into the intake manifold.

Another problem very similar to this is that the spring loaded valve doesn’t work.  This will lead to some of the earlier problems.

A PCV system can lead to some other problems such as MAF codes or other induction sensors.  This is due to the fact that if the system is not working correctly it can blow oil back into the intake and this oil can coat your MAF sensor and cause all kinds of problems.

After discussing some of the problems and symptoms of a PCV system not working correctly we can go into the diagnosis procedure.

  1. You will have some reason or complaint to check the PCV system before starting this, or else you simply want to make sure that it is working.
  2. After deciding you are going to check your PCV system it is time to start the diagnosis.  The first thing to look at is the hoses.  Make sure that all of the hoses look like they are connected and in good shape.  If you see any kinked or broken hoses replace them.
  3. Next you will want to check to make sure there are clamps on the hoses.  Some hoses do not require clamps but if they have a clamp on them make sure it is snug and doesn’t move.  Replace clamps as necessary.
  4. The last thing that you will need to look at is the PCV valve itself.  There are several tests that can be done to check to see if it is working.  The most common is the rattle test.  You will shake the PCV valve and if it rattles it is good, I do not like this test because it is not always true.  The test I prefer is the paper test.  Have the engine running and simply take a piece of paper and remove your oil cap.  Set the piece of paper on the oil cap and it should be sucked down and held in place by vacuum.  If not your PCV valve is not working.  Another similar test would be to remove the PCV valve and hose and hold your finger under the valve it should suck your finger against the valve if it is working correctly, this is with the engine running.

Now that we have gone through some of the diagnosis of your PCV system we can discuss how to replace any part of the PCV system.

  1. Park your vehicle.
  2. Diagnose the problem and what you have to do to fix it.  The first item we will discuss how to fix is a broken hose.
  3. Use a plier such as this  Slip Joint Pliers to remove any clamps holding the hose in place.
  4. Remove the hose.
  5. Reinstall the new hose.
  6. Use the pliers to position the clamp in place.
  7. If you have a PCV valve that is faulty simply remove the hose that goes to the PCV valve itself.
  8. Remove the PCV valve.
  9. Install the new PCV valve.
  10. Reconnect the hose to the PCV valve.

You just finished diagnosing and fixing your PCV system on your vehicle.  I hope this helps you to better understand how to work on the PCV system on a vehicle.


Written by: Cody Mammenga an NDSCS Student

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