'Fast N' Loud' Host -- I Got Screwed Promoting O-O-O O'Reilly, Auto Parts ... OH!!!

"Fast N' Loud" host Richard Rawlings says he broke his back promoting a famous auto parts store and all he got was the shaft.

Rich says in a new lawsuit, he signed on with the company that does marketing for O'Reilly Auto Parts to make personal appearances and sing the virtues of O'Reilly on social media sites. Rich also owns a car shop and agreed to slap O'Reilly banners on the walls.

In return for his good work, Rich says he was promised a cool $100k.

Rich says he's been shorted by $40k and is now suing for payment.

We reached out to a rep for the marketing company. So far ... no word back. Oh!!!