Famous TV 'Repo' Man -- Nabs Car Chase Suspect ... You're Welcome Cops!

The star of "Operation Repo" was Johnny-on-the-spot ... ending a L.A. car chase by blocking the fleeing suspect until cops could arrive -- but no one recognized him due to his extreme weight loss.

Lou Pizarro played the hero at the end of the chase -- which, of course was televised (this is L.A.) -- when the suspected car thief abandoned the vehicle ... and tried to run away on foot.

Pizarro -- who's been hauling in vehicles on 'Repo' for 8 years -- happened to be in the right place with the famous red pickup truck he uses on the show. Pizarro made a hard right turn to pin the suspect up against a fence ... allowing cops to catch up to the guy.

Here's the thing ... local news talked to Pizarro after the chase, but never recognized the TruTV star -- probably because he's half the man he used to be. We're told Lou's dropped about 150 pounds after getting a gastric sleeve 15 months ago!

Way to go, not-so-big guy.