As emission regulation got stricter, in 1979, the Ferrari 400 got an updated engine. Instead of the six carburetors, the V12 received a Bosch K-Jetronic fuel injection system. This meant a greater improvement regarding emissions, but it took power down from 340 HP to 310 HP. The only visible difference between the 400 and the 400i was exactly the "i" badge on the tail.
Later models came with different camshaft profiles and exhaust headers, gaining 5 HP. Interior changes were also made towards the end of the 400i's lifespan, with different upholstery, door panels, and electronic switchgear. Minor exterior changes were also done. The model retained the standard 5-speed manual (400i GT) and the optional 3-speed automatic gearbox (400i Automatic). A total of 1,305 units were made.
Source: www.topspeed.com; www.autoevolution.com