How to Troubleshoot a Car Engine PCV System

Positive crankcase ventilation valve and connection to valve cover. 1977 Ford Taurus V4 engine.

As part of the important emissions control system in your car, the positive crankcase wentilation system’s (PCV) primary function is to route toxic vapors out of the crankcase-main engine block-into the intake manifold for reburning in the combustion chamber. This prevents fumes not only from polluting the atmosphere but corroding engine parts, building sludge and diluting oil. Problems in the PCV system may cause an engine to idle unevenly, increase idle speed or stall. Here we will go through some simple steps for you to troubleshoot and repair the PCV system in your own vehicle. So let’s start.

Things You'll Need

• Solvent

Instructions

1. Locate the PCV valve. Most likely you will find it in the valve cover, on the oil filler cap or around the intake manifold.

2. Take a close look at the PCV valve, hoses, connectors and eyelets or grommets around openings. Make sure they all are in good condition. Replace any part if necessary.

3. Follow the PCV hoses, starting at the valve cover. Disconnect and inspect one by one. Make sure they are not hardened, softened, cracked or clogged. If any hose if filled with sludge, use wire and solvent to clean it. Replace any damaged hose.

4. Inspect the breather filter. Most PCV breather filters can be removed and cleaned with solvent. If your PCV system uses a wire mesh breather filter, clean it with solvent, dip it in oil and reinstall.

5. Check and test the PCV valve. Unplug the valve from the valve cover or intake and shake it with your hand. You should hear a rattling sound. If you do not hear it rattle, replace it.

6. Turn on the engine and let it idle. Pull the PCV valve from the valve cover or intake manifold and place your finger at the end of the valve. You should feel the vacuum at the tip of your finger and engine RPM should drop bellow 100 but not more than 40. If not, the valve, a hose or passage is clogged. Inspect the hoses, fittings and clean as necessary. If the valve is clogged, replace it. If the RPM goes bellow 40, the PCV valve might be stuck open. Check it and replace if necessary.

Tips & Warnings

• Some PCV valves will not rattle when shaken. They come as a single unit and should be cleaned when necessary and reinstalled. The 1987 Ford Escort station wagon uses this type of valve.

• Consult the service manual for your particular vehicle to easily locate engine parts. You can buy a vehicle service manual at most automotive parts stores or consult one for free at most public libraries.

• Replace a PCV hose only with oil resistant type or a molded hose as required.