VW "4-banger" really bangs!

We have a VW Golf with 70K miles and 9 years old. All of a sudden the engine sounded like one of the spark plugs was removed. It was running on 3 cylinders and you could actually feel air being forced out of the engine at the cylinder on the driver’s side. It was not hot or seemed to be containing fuel. It felt like it might be coming from around the oil filler hole or around the cylinder cover. What could be the problem?

We had a similar post last year where a VW owner wrote that his car popped a spark plug.

If the plugs are not in sufficiently tight, this could indeed happen. Take the car to a good mechanic and he will find very quickly what is wrong.

Does your engine have a extensive engine cover? maybe this is why opening the hood and giving the engine a look over does not help you determine if a spark plug has blown out.

The info about pressure out oil filler is disturbing,but lets not get into that until you post back that all the spark plugs are still tight.

Yep, your right about the engine cover. Couldn’t feel the gas escape until it was taken off but the noise was pretty loud. The “air” didn’t seem to be escaping from the plug hole, it seemed to be above that. Right where the oil filler cap was but the cap hadn’t been blown off or was loose. (All the plugs were there and didn’t appear to be lose.) I am wondering if it could be the valve cover gasket? I’ve never seen anything like this before in my 55 years.

You might have a PCV valve that is stuck. If that is the case, pressure builds up in the crankcase, and this can lead to any number of undesirable situations, including the breach of some gaskets.

Before you do anything else, pull the PCV valve, and shake it to see if it rattles. If it does not rattle, then it is stuck and needs to be replaced for a cost of…maybe $2.50 or thereabouts. Even if it does rattle, insert a small screw driver into the bottom orifice of the PCV valve to be sure that it moves freely. Even though a PCV valve is cheap, when it sticks, it can lead to a whole WORLD of problems.

Incidentally, if the PCV valve turns out to be gummed up, this means that you are not changing the oil and doing general maintenance on the engine often enough. Since you apparently drive less than 8,000 miles per year, you still need to change the oil at least twice a year. Personally, I would change the oil every 3 months, given that engine’s reputation for oil sludging.

Just to reiterate - the noise is similar to a mild explosion. Very loud sound from one of the four cylinders. I will check out the PCV for sure, though.

Can you post a picture of where the air is coming from? Rocketman

If the plugs are OK, the next place such noises could come from is a broken exhaust manifold, or the gasket has fallen out.

I also had this problem with an old Ford V8 with a smog pump that imjects air into the exhaust. The air tubes had corroded and the exhaust pressure forced out the gasses under the hood, making a noise similar to what you describe.

Docnick, you were right! You can’t see the #2 and #3 plugs well due to the intake manifold but the mechanic spotted it right away. Thanks for the suggestion- #3 had been working it’s way out for a very long time since they have never been changed.

Thanks to everyone with their suggestions! Yes, it was a plug that had worked itself loose. I have never had this happen before but VWs seem to be prone to this.