On February 22, 2016, at 1334 Pacific standard time, a Mooney M20J, N201KY, experienced a loss of engine power after takeoff and the pilot made a forced landing onto a city street near Whiteman Airport (WHP), Pacoima, California. The airplane was operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. The private pilot was not injured. The airplane sustained substantial damage during the accident sequence. The local personal flight departed Pacoima about 1330. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that about three minutes after takeoff the engine started to run rough. He contacted the tower controller and advised that he was turning back. While on short final, he pulled back on the power and the engine lost power. The pilot was able to re-start the engine but it again lost power. The pilot was unable to make it to the runway and subsequently initiated a forced landing to a city street. During the landing, the airplane struck a moving car and numerous parked vehicles; substantially damaging both wings and the fuselage. The airplane was recovered to a secured facility for a postaccident engine examination. The engine was visually examined and determined that an engine run was possible. The engine was subsequently mounted onto an engine test stand. No modifications were accomplished except to add oil which had leaked out during storage. The engine started and was run at 2,700 rpm and 28 inches of manifold pressure. A magneto check was accomplished which recorded a 50 rpm drop. When the rpm was reduced to 1,200 rpm, it was noted that the engine ran lean. A review of the maintenance logbooks revealed a discrepancy as to when the last annual/100 hour inspection was accomplished. An entry dated 6/15/15 identified a recoding tach time and total time in service of 2,052 hours. A sticker had been applied to the page indicating "Remove plugs check compression. Removed injectors and cleaned and inspected IAW 100 hr and was determined to be in an airworthy condition." There was no mechanics signature, certificate number and Inspection Authorization identified for return to service. A previous hand written entry dated 2/1/13, indicated that the engine had been inspected in accordance with a 100 hour inspection and was determined to be in an airworthy condition. This entry revealed the appropriate mechanic signature and certificate number. The mechanic reported that he did not inspect the engine on 6/15/15.