Volkswagen Golf/Jetta 2 manual

General information and precautions
Fuel and exhaust systems - K-Jetronic fuel injection - 8 valve engines / General information and precautions


General information
The principle of the K-Jetronic continuous injection system is very simple and there are no specialised electronic components. There is an electrically driven fuel pump and electrical sensors and switches but these are no different from those in general use on vehicles (see illustration).

1.0 K-Jetronic fuel injection system air intake components - 8v engine
1.0 K-Jetronic fuel injection system air intake components - 8v engine

The following paragraphs describe the system and its various elements. Later Sections describe tests which can be carried out to ascertain whether a particular unit is functioning correctly. Repairs are not generally possible.

The system measures the amount of air entering the engine and determines the amount of fuel which needs to be mixed with the air to give the correct combustion mixture for the particular conditions of engine operation. Fuel is sprayed continuously by an injection nozzle to the inlet port of each cylinder. This fuel/air mixture is drawn into the cylinder when the inlet valves open.

Airflow meter
The airflow meter measures the volume of air entering the engine and comprises an air funnel with a sensor plate mounted on a lever which is supported at its fulcrum. The weight of the airflow sensor plate and its lever are balanced by a counterweight and the upward force on the sensor plate is opposed by a plunger. The plunger, which moves up and down as a result of the variations in air flow, is surrounded by a sleeve having vertical slots in it. The vertical movement of the plunger uncovers a greater or lesser length of the slots, which meters fuel to the injection valves.

Fuel supply
The fuel pump operates continuously while the engine is running, excess fuel being returned to the fuel tank. The pump is operated when the ignition switch is in the START position. Once the starter is released, a switch which is connected to the air plate, prevents the pump from operating unless the engine is running.

The fuel line to the fuel supply valve incorporates a filter and also a fuel accumulator. The function of the accumulator is to maintain pressure in the fuel system after the engine has been switched off and so give good hot restarting.

Associated with the accumulator is a pressure regulator which is an integral part of the fuel metering device. When the engine is switched off, the pressure regulator lets the pressure to the injection valves fall rapidly to cut off the fuel flow through them and so prevent the engine from УdieselingФ or Уrunning onФ. The valve closes at just below the opening pressure of the injector valves and this pressure is then maintained by the accumulator.

Fuel distributor
The fuel distributor is mounted on the air metering device and is controlled by the vertical movement of the airflow sensor plate.

It comprises a spool valve which moves vertically in a sleeve, the sleeve having as many vertical slots around its circumference as there are cylinders on the engine.

The spool valve is adjusted to hydraulic pressure on the upper end and this balances the pressure on the air plate which is applied to the bottom of the valve by a plunger. As the spool valve rises and falls, it uncovers a greater or lesser length of metering slot and so controls the volume of fuel fed to each injector.

Each metering slot has a differential pressure valve, which ensures that the difference in pressure between the two sides of the slot is always the same. Because the drop in pressure across the metering slot is unaffected by the length of slot exposed, the amount of fuel flowing depends only on the exposed area of the slots.

Cold start valve
The cold start valve is mounted in the inlet manifold and sprays additional fuel into the manifold during cold starting. The valve is solenoid operated and is controlled by a thermotime switch in the engine cooling system. The thermotime switch is actuated for a period which depends upon coolant temperature, the period decreasing with rise in coolant temperature. If the coolant temperature is high enough for the engine not to need additional fuel for starting, the switch does not operate.

Warm-up regulator (valve) While warming up, the engine needs a richer mixture to compensate for fuel which condenses on the cold walls of the inlet manifold and cylinder walls. It also needs more fuel to compensate for power lost because of increased friction losses and increased oil drag in a cold engine. The mixture is made richer during warming up by the warm-up regulator. This is a pressure regulator which lowers the pressure applied to the control plunger of the fuel regulator during warm-up. This reduced pressure causes the airflow plate to rise higher than it would do otherwise, thus uncovering a greater length of metering slot and making the mixture richer.

The valve is operated by a bi-metallic strip which is heated by an electric heater. When the engine is cold, the bi-metallic strip presses against the delivery valve spring to reduce the pressure on the diaphragm and enlarge the discharge cross-section. This increase in cross-section results in a lowering of the pressure fed to the control plunger.

Auxiliary air device
Compensation for power lost by greater friction is achieved by feeding a larger volume of fuel/air mixture to the engine than is supplied by the normal opening of the throttle.

The auxiliary air device bypasses the throttle with a channel having a variable aperture valve in it. The aperture is varied by a pivoted plate controlled by a spring and a bi-metallic strip.

During cold starting, the channel is open and increases the volume of air passing to the engine. As the bi-metallic strip bends, it allows a control spring to pull the plate over the aperture until at normal operating temperature the aperture is closed.

Cold acceleration enrichment This system is fitted to later models only.

When the engine is cold (below 35∞C), acceleration is improved by briefly enriching the fuel mixture for a period of approximately 0.4 seconds. This cold acceleration enrichment will only operate if the thermotime switch, the diaphragm pressure switch and the throttle valve switch are shut off.

Temperature sensor
From March 1986, a temperature sensor is located between injectors 1 and 2. After switching off the ignition, this switches on the cooling fan when the temperature of the cylinder head exceeds 110∞C. A time relay is incorporated in the circuit. This switches off the function between ten and twelve minutes after switching off the ignition.

Precautions
Fuel warning
Many of the procedures in this Chapter require the removal of fuel lines and connections which may result in some fuel spillage. Before carrying out any operation on the fuel system, refer to the precautions given in Safety first! at the beginning of this Manual and follow them implicitly. Petrol is a highly dangerous and volatile liquid and the precautions necessary when handling it cannot be overstressed.

Fuel injection system warning Residual pressure will remain in the fuel lines long after the vehicle was last used, therefore extra care must be taken when disconnecting a fuel line.

Loosen any fuel line slowly to avoid a sudden release of pressure which may cause fuel spray. As an added precaution, place a rag over each union as it is disconnected to catch any fuel which is forcibly expelled.

Take particular care to ensure that no dirt is allowed to enter the system. The ignition must be off and the battery disconnected.

Unleaded petrol - usage
Refer to Part A of this Chapter.

Catalytic converters
Before attempting work on these items, carefully read the precautions listed in the following Section.


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