12/6/2023 0 Comments Sequential multi port injection![]() The injectors fire just before each intake valve opens. The poppet valves in the spray nozzles also open at a slightly lower pressure (about 40 psi). The system also uses a mass airflow sensor to monitor airflow.įuel pressure in the CSFI system is a bit higher than the CPI system (60 to 66 psi with key on engine off), and the regulator maintains the operating pressure at 55 to 57 psi. On the second-generation Central Sequential Fuel Injection (CSFI) system (1996 and up), the MAXI injector in the central housing has been replaced with six individual injectors, each of which feeds fuel to its own poppet spray nozzle. If one comes loose, it can spray fuel where fuel doesn’t belong and create a potential fire hazard. Once that is out of the way, the six individual spray nozzles can be pulled out of the bottom half of the manifold by squeezing the plastic prongs together and pulling (sort of like pulling apart an electrical connector).Ĭaution: When installing the CPI system, make sure the poppet nozzles are securely locked in position in the lower half of the intake manifold. There are 10 Torx fasteners that hold it in place. To replace the CPI assembly, the top of the intake manifold plenum has to come off. If the inside of the manifold is shiny or you can see fuel stains or leaks, the CPI is leaking and needs to be replaced without delay. Warning: If the engine compartment smells like gasoline, remove the manifold tuning valve located on top of the intake manifold and look inside with a flashlight. The important point to note about the CPI system is that if anything in the CPI system fails (the MAXI injector shorts out, goes open or leaks, the fuel pressure regulator leaks, any of the lines that connect the MAXI injector to the nozzles leak or break, or any of the individual nozzles leak or become plugged up), the whole system must be replaced as a complete assembly. The injector driver circuit uses the peak-and-hold method, providing 4 amps to open the injector and about 1 amp to keep it open. The PCM varies the on-time or dwell of the MAXI injector to control the air/fuel mixture. Fuel delivery is controlled by pulse width modulation. The powertrain control module (PCM) estimates air flow using inputs from the MAP sensor, throttle position sensor, temperature sensor and engine speed. The CPI system is a speed-density system, so there is no airflow sensor. This allows the system to provide sequential fuel injection for better emissions, performance and fuel economy. In the second generation CSFI system, the injectors are controlled individually and fire only once every other revolution of the crankshaft. In the first generation CPI system, all the nozzles spray simultaneously when the MAXI injector opens (three times per crankshaft revolution). ![]() 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. 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. Fuel injectors are expensive, so using one injector instead of six seemed like a good idea at the time. Some bean counter at GM probably came up with the idea as a way to reduce costs. 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. The system was also added to 5.0L and 5.7L Vortec V8 engines. The system was used on 4.3L V6 Vortec engines through 1995, and was redesigned in 1996 and renamed “Central Sequential Fuel Injection” (CSFI). 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). ![]()
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