Back in 1992, General Motors introduced a new type of fuel injection system known as "Central Port Injection" (CPI), which GM also refers to as "Central Multi-point Fuel Injection" (CMFI). The system was used on 4.3L V6 Vortec engines through 1995, and was redesigned in 1996 and renamed "Central Sequential Fuel Injection" (CSFI). The system was also added to 5.0L and 5.7L Vortec V8 engines.

Though the CPI system supplies fuel to each of the engine's intake ports like other multi-port fuel injection systems, it has only one centrally located fuel injector, called the MAXI injector. Some bean counter at GM probably came up with the idea as a way to reduce costs. Fuel injectors are expensive, so using one injector instead of six seemed like a good idea at the time.

Here's how it works:

The MAXI injector is mounted in the center of the intake manifold on the 4.3L engine, and is hidden inside the split plenum manifold. Instead of spraying fuel directly into the manifold like a throttle-body injector, the MAXI injector routes fuel into six nylon fuel lines that have poppet-style spray nozzles on the end. When the pressure inside the lines reaches the opening pressure of the poppet valves (43 psi), fuel sprays out of the nozzles into the engine's intake ports.

In the first generation CPI system, all the nozzles spray simultaneously when the MAXI injector opens (three times per crankshaft revolution). In the second g...