MPV engine number &noisy engine when revved.

Hello all,

Please i will appreciate if someone could help me locate my engine number, I bought a used MPV 2000, need it for the paper work and its done about 101,000 milleage, I cant seem to find it.

Also changed the oil over the weekend, the original oil in the engine was darkened green with relative higher viscosity. And it sounded just okay then.

Tried changing the plugs but noticed they were platinium plugs with different threading so i returned the plugs.

Now the engine sounds funny when its revved, anyone in the house with a fix or advice for me?

Thanks in advance.