Speed density was the first fuel control system used on 1982-1984 Corvettes. It was also used on the 1990-1993 cars. Speed density uses a manifold absolute pressure sensor (MAP sensor) to calculate the necessary fuel load. The 1990-1991 cars have a MAP sensor bolted directly to the intake plenum. The 1992-1993 cars have the MAP sensor bolted to the intake manifold. The throttle position sensor, coolant temperature sensor, and intake air temperature sensor are also used to calculate fuel.
Mass-air flow fuel control was introduced in 1985 and used until 1989. It was reintroduced in 1994 along with sequential fuel injection. The 1985-1989 mass-air system had a few changes along the way.
1985 cars have a slower baud rate computer and use a mass-air sensor module to control burn-off and to power the mass-air sensor.
1985-1988 cars use a stand-alone cold-start system that requires intake manifold porting to allow cold start fuel flow. This porting hurts power output.
1989 cars had no cold-start system, along with intake manifold porting changes. The 1989 cold start event is handled by the PROM (chip). The fuel injector pulsewidth was increased. 1986-1989 computers were replaced with a faster baud rate unit.
1994 cars have an On Board Diagnostic (OBD) system (first generation). The OBD system was introduced to bring diagnostic uniformity to all makes and manufacturers. The 1994-1996 OBD computer system utilizes mass-air and MAP sensors to control fuel delivery. The 1994-1996 cars utilize sequential fuel injection, which means fuel is injected only when needed. These cars have better fuel control and respond better to high performance modifications.
The 1995-1996 cars have OBDII fuel control systems that follow more stringent fuel emission control standards. Catalytic converters have oxygen sensors checking their performance as well as controlling fuel in closed loop.