Porsche 911 Mechanical Fuel Injection Trouble Shooting (1965 - 1989)

One of the most complicated fuel delivery systems ever created was the Bosch mechanical fuel injection system, or MFI.
The system was a precursor to the more modern electronic controlled fuel injection systems, and is actually a marvel of mechanical engineering. The system functions in a similar manner to the electronic systems that followed it, yet all the controls were almost completely mechanical. As a result, there is lots of tuning and adjustment required for the complicated system.
Unfortunately, there isn't a whole lot of information available on the subject. This project will give an overview of the MFI system, and also some pointers on tuning and adjusting it. For more information, it is recommended that you consult the factory workshop manuals, or if you can find it, the Porsche technical bulletin "4532.20 Check, Measure, Adjust" for the mechanical fuel injection system.
The MFI system consists of two main parts, the injection/distribution pump, and the throttle bodies. The electric fuel pump located in the front of the car supplies pressurized fuel to the injection/distribution pump. The injection pump is the heart of the system, and is responsible for metering and providing the fuel to each cylinder. The pump itself consists of two main parts, the fuel pump assembly, and the compensating unit. The fuel pump assembly is responsible for the actual delivery of fuel to each of the cylinders, while the compensating unit is responsible for adjusting the fuel delivery according to the levels set by both the accelerator and the speed of the engine. Precise coordination of all the elements of the engine are required for the system to function properly...
Read the Full Article: www.pelicanparts.com/techarti...