New Fuel Injection System for the 911

By C.A. Stoddard
National Technical Chairman

Type 911-T Porsches produced since January 1973 feature a fuel injection system which is very different from any injection system used previously, It was developed in collaboration with Bosch, and will be further integrated into 1974 Porsches. It has many outstanding features which may all be summarized in one word, "simplicity".

The recent incentive for any automobile manufacturer to use a fuel injection system is to help meet the governmental ecology requirements, which are becoming increasingly difficult. Injection systems supply each cylinder with a metered amount of fuel, thus providing more nearly equal and complete combustion in each cylinder, than is possible with a carburetor system.

This new system is called the KA Injection, or CIS system. KA and K-Jetronic are German designations—K for continuous, A for non-powered. CIS is the U.S. designation—continuous injection system. This system tackles the combustion problem one step before its predecessor; it measures the total air flow going into the engine, and then injects a total desired amount of fuel, and divides it equally between the 6 cylinders.

Because the basic concept is to sense air flow, there are no mechanical connections to the engine. Gone are the timing belt and numerous rods and linkages which are sensitive to adjustment and wear. The only external linkage is to the accelerator pedal. The system is clean in design as well as ecology-wise, and is physically more compact and lighter than previous systems. It gives excellent driveability, throttle response, idle, no backfire, and in general, runs very smoothly with increased gas mileage.

Maintenance is simple, with 2 filters (air and fuel), and only 2 basic adjustments. The adjustments allow for idle speed and CO regulation, and tend to be very stable.

Below is a schematic of the system with the main components numbered 1 through 13.

A simplified explanation of each component is as follows: 

1. Fuel Tank—Similar to previous 911 tanks and located in the usual place. However, it is not interchangeable with previous years because it incorporates a special "whirl pot" at the fuel line to prevent the possibility of any air bubbles entering the injection system. Capacity is 16.4 gals. for 1973.
2. Fuel Delivery Pump—An electric roller cell pump, similar to previous designs
3. Accumulator—An expansion chamber in the fuel feed line which internally has a spring loaded diaphragm. It provides a damping action to the fuel flow, and keeps the system under sufficient pressure when the engine is stopped for short periods.
4. Fuel Filter—Typical of the requirements of most fuel injection systems—it has a paper filter insert which must be serviced periodically.
5. Fuel Distributor—Fuel is equally distributed to 6 cylinders under controlled pressure from the fuel pump via variable slit openings.
6. Air Sensor—A large specially contoured funnel opening through which all (filtered) air flows. The flowing air positions a sensor plate which is balanced by a lever acted upon by fuel control pressure and a balance weight.
7. Control Pressure Regulator (Temperature)—Correct air/fuel ration and mixture compensation for engine and outside temperature change is provided by this component mounted on the crankcase.
8. Throttle Valve—A butterfly type valve positioned by the accelerator, which regulates engine speed and/or power.
9. Control Pressure Regulator (Throttle)—Accelerator pedal position varies the fuel control pressure; this regulator is mounted on the throttle shaft.
10. Injection Valve—Into each cylinder inlet port, one of these injection valves continuously meters fuel, where it is "stored" while waiting for the intake to open.
11. Start Valve—An additional (7th) injector which sprays fuel into the main air flow during the starting cycle. The hand throttle must be pulled fully up to activate the electromagnetic switch which controls the fuel flow to this injector.
12. Idle Speed Adjustment—Throttle bypass air is adjusted to obtain idle speed.
13. Basic CO Adjustment—Obtained at idle speed, this adjustment screw is on the air sensor lever, and requires a special tool for setting.

This system, by nature of its design, is most sensitive to air leaks. Therefore, curious PCA’ers are cautioned to carefully position and secure any covers removed for inspection. 

7/73

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