How to Determine if the PCV Valve is Faulty?
4 Answers
PCV valve functionality can be determined by checking for oil presence and observing engine operation. Here are the detailed methods: 1. Checking for oil: You can directly loosen the throttle body clamp screw, remove the air hose, wear gloves to open the throttle body, then insert the oil dipstick all the way to the bottom and pull it out for inspection. If the dipstick only shows some oil dust, there's no issue, but if there's actual oil present, it indicates a faulty PCV valve. 2. Observing engine operation: Start the engine and let it idle, then remove the vacuum hose from the PCV valve and connect a manual vacuum pump. Apply vacuum directly to the PCV valve diaphragm chamber. Normally, the engine should exhibit unstable idle or stall, which indicates the PCV valve is functioning properly. If this doesn't occur, it proves the PCV valve is damaged.
As an experienced mechanic, I'm used to diagnosing PCV valve issues based on engine symptoms. First, listen to the idle sound - a faulty valve causes engine surging with the tachometer needle dancing erratically. Pull out the dipstick; if white smoke comes puffing out of the crankcase, there's a 90% chance the PCV valve is leaking. The most direct test is to remove the valve's hose after warming up the engine and block the opening with your finger - a good valve should create suction holding your finger. No suction or reverse airflow means the valve is definitely bad. Last time I encountered a BMW N20 engine burning oil excessively - turned out the valve diaphragm was cracked, sending all the oil vapor into the turbocharger. These little details help car owners detect problems early, saving major repair costs.
As a driver who frequently takes long-distance trips, I diagnose exhaust valve issues through driving experience. When you feel the throttle is sluggish with delayed power response during acceleration, and there's a sudden increase in fuel consumption, it's time to be alert. Last time, my car emitted blue smoke from the exhaust. After stopping to check, I found the engine top covered in oil sludge. When I pulled out the exhaust valve and shook it, there was no clicking sound—instead, about half a tube of engine oil poured out. After replacement, the power immediately became smoother, and on the highway, fuel consumption dropped by 2 liters per 100 kilometers. I recommend everyone to clean the throttle body during maintenance, as excessive carbon buildup can affect the exhaust valve's operation.
Here's how we test the wastegate in car modifications: After a cold start, cover the valve outlet with a plastic sheet. Under normal conditions, the vacuum should firmly hold the sheet in place. If it doesn't hold or there's a hissing sound from air leakage, the valve might be stuck or malfunctioning. A more accurate method is to remove the valve and blow through it; it should only allow one-way airflow to be considered normal. Once, after installing a turbo, the engine experienced knocking. After a lengthy inspection, we found that a clogged wastegate caused excessive crankcase pressure, forcing the valve cover gasket to blow out. Regularly cleaning oil sludge from the valve body can extend its lifespan.
