Soulja Boy's getting a heavy dose of reality ... TMZ has learned the "Crank That" rapper's just been added to the cast of "Love & Hip Hop: L.A" -- in a last-ditch effort to pump some life into the show.
Sources close to production tell us ... the show's been struggling with weak story lines and uninteresting characters ... and producers felt they needed to add a big name rapper to liven things up.
Right now ... Ray J is the biggest star on "L&HHLA" ... and producers think he and Soulja Boy will be a huge hit together. Sources close to Ray J say he's pumped about his new co-star.
If it's drama they want ... the sizzurp-slurpin' Soulja should bring plenty of it.