I have a 2001 Nissan Altima with 134,000 miles. Here are a list of the issues I am having:

check engine light on. reading was - knock senor and/or catalytic converter.

Looks like there is oil splattered all over my engine.

Smell of fumes inside the car, especially when heat is on.

Is one thing causing this or is this multiple problems, having it check out this week but wanted some advice before heading to the mechanic.

Thanks.