Hi, I am new New to Mercedes Diesels..when should I change the timing belt? Also, what is this thing called a vacuum pump and whre is it? Finally it runs funny and a friend suggested U should check my P timing. Where is the P? An Also, what is the purpose of the gunsight on the hood? Is that to check your alignment? Finally I have looked all over the engine and I can find oil filter easy enough, of course is that filter near the #1 cylinder on the passenger side of the engine. Yes I did change the oil! Now where is the fuel filter?