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Mechanical fuel injection systems first saw light of day at the turn of the century, however the following 100 years has seen the system evolve from a very basic and almost crude fuel delivery system, to the recent mass produced versions of the Bosch K and KE Jetronic. The mechanical fuel injection system has recently been overshadowed by modern electronic injection, which enables the use of lambda closed loop control. The electronically modified Bosch KE also has this capability although it never achieved the popularity of the pure mechanical system.This following overview is a brief description of the system. Bosch K Jetronic operational overview The system may seem very complicated at first, but it can be broken down into specific areas and fault finding is therefore made easier.Fuel is delivered from the fuel pump to a metering (or fuel distribution) head and depending on the engine’s temperature, the correct amount of fuel is delivered via the injectors to the engine. The injectors on this system spray fuel continuously in a fine atomised spray into the inlet manifold.Cold start and the warm-up period are also catered for by a cold start injector and a reduction in the control pressure. The idle speed is increased by the auxiliary air valve.The fuel pump will have the ability to provide a huge amount of fuel from the tank of which 99% will be returned. Due to the nature of this system, specialised equipment may be needed. The injectors fitted to this system will open at a predetermined pressure and will spray a fine atomised ‘mist’ of fuel behind the inletvalve, waiting to be drawn in on the induction stroke. The fuel is delivered into the engine in a continuous spray and is not timed orpulsed as on other systems. The opening pressure of the injector is at approximately 3.3 bar at which point fuel is injected into the manifold; when the injector pintle opens this will cause the pressure to drop, subsequently closing the injector, which causes the pressure to rise once again and this will of course open the injector. This pintle vibration is called ‘chatter’ and helps to atomise thefuel before it’s induction.When the engine is switched off the fuel pressure drops below 3.3 bar and the injector closes forming a fuel tight seal, helping to avoid fuel dripping into the inlet manifold.The spray pattern should be a conical shape and when clean and working efficiently, should emit a high frequency noise: this is the sound of the pintle ‘chatter’.

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