How many welsh plugs?
 

I have a Volkswagen transporter 2.0 L petrol. I've had 3 welsh plugs at the back of the engine replaced. I've also heard a rumour that there is another one at the front of the engine, but the mechanic couldn't find it. Who can tell me,

"How many welsh plugs are there in Volkswagen transporter 2.0 L petrol engine?"

Thanks in advance!