Sour Diesel is a strain of Marijuana that’s very popular among rappers & weed smokers alike. Due to him being an extremely fast car, racing other cars (rappers), he’s leaving his competition “smoked” like Sour Diesel.
Tailing the word “diesel”, and making another reference to being a car, he takes time to mention that he uses diesel fuel. Though, typically, only trucks such as 18-Wheelers use diesel fuel. This is likely also a clever way of saying that his competition fuels him.