Sometimes this system is also referred to as a "Bosch CIS" injection system, which stands for Continuous Injection System, technically it is referred to as "K-Jetronic". This is because the injectors are not "pulsed" like electronic injectors. The injectors are mechanical and inject fuel into the cylinders continuously, while the engine is running.  The injector (one per cylinder) contains a spring and plunger. When the fuel pressure exceeds the spring force of the injector the injector begins to flow and allows fuel to flow into the intake manifold. When the intake valve is opened the fuel is drawn into the cylinder where it is burned.  When the engine shuts down the fuel pressure in the system drops and the plunger in the injector prevents fuel from leaking into the intake manifold. See Figure 1 - Bosch Continuous Injection System.

Figure 1 - Bosch Continuous Injection System
(Numbered Items Refer To Items On Image)

1. Fuel Distributor
2. Fuel Tank
3. Fuel Pump
4. Fuel Accumulator
5. Fuel Filter
6. System Pressure Regulator
7. Fuel Injector

The fuel distributor meters how much fuel flow is delivered to the injectors based on how much air is being drawn into the cylinders, which in turn is based on throttle position and engine RPM.   The fuel distributor is mechanically linked to an air flow sensor which contains a plate connected to a mechanical lever. The plate is located in the air flow stream of the engine, usually it is integrated into the air filter box. See Figure 2 - Air Flow Meter & Fuel Distributor.

Figure 2 - Air Flow Meter & Fuel Distributor
(Numbered Items Refer To Items On Image)

1. Air Flow
2. Control Pressure
3. Fuel Inlet (from fuel supply pump)
4. Fuel Outlet (to injectors)
5. Control Piston/Plunger
6. Control Cylinder
7. Fuel Distributor

As air is drawn into the engine the plate moves and intern pushes the control piston up in the control cylinder's bore. As the piston moves it exposes small slits (vertical openings) in the control cylinder, the size of the opening controls how much fuel is supplied to the injectors. The more air that flows to the engine the larger the opening and therefore more fuel is supplied to the cylinders. See Figure 3 - Control Piston & Cylinder and Figure 4 Control Cylinder with Metering Slits.

Figure 3 - Control Piston & Cylinder
(Numbered/Lettered Items Refer To Items On Image)

a. Inoperative (no flow to injectors)
b. Part Load Operation (medium fuel flow to injectors)
c. Full Load Operation (maximum fuel flow to injectors)

1. Control Pressure
2. Control Piston/Plunger
3. Fuel Outlet Port (to injectors)
4. Metering Slit In Outlet Port
5. Fuel Inlet (supply)
6. Control Cylinder

Figure 4 - Control Cylinder with Metering Slits
NOTE: The actual slit size is only about .2mm (.0078") wide!

Internally the fuel distributor has many o-rings and springs.  Each metering slit contains an o-ring which isolates each cylinder. Each cylinder also has a fuel metering regulator, technically referred to as a "Differential Pressure Regulator", which contains a spring, metering disc and sometimes a precision ground shim. See Figure 5 - Fuel Distributor Internals

Figure 5 - Fuel Distributor Internals

The fuel distributor is susceptible to several failure modes; contamination, o-ring failure (leakage) and  diaphragm leaks to name a few.  The fuel distributor is a precision device and the control piston and control plunger are precision ground to within .0005" of each other. Any contamination that enters the fuel distributor can cause major problems, requiring it to be replaced with a remanufactured unit. The remanufacturing process takes special equipment such as fuel metering benches and of course the necessary parts that will require replacement (0-rings, diaphragms,  springs, etc.).

Symptoms of a fuel distributor failure are numerous in nature. They can range from a failure to start, to engine flooding (too much fuel), fuel starvation (not enough fuel), inconsistent fuel flow between cylinders to a hesitation stall or stumble. 
 

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Note: This section is designed to help explain the operation of the fuel distributor and is in no way a replacement for factory service information, diagnostic information, or technical training. This information is only brief introduction to a complicated system which often requires special tools, training and vehicle specific technical manuals.  It is provided as courtesy to our visitors and although believed to be accurate Jaytan assumes no liability for completeness or accuracy. Use at your own risk.