INJECTORS
The fuel is injected into the engine cylinders by means of injectors of the forward opening poppet-valve type.

Figure 11 shows the main features of the injector. Fuel enters the injector at the top. The nozzle valve is kept closed by spring pressure. The valve is designed to open at 50 lbf/in2 (344.73 kN/m2). The correct amount of fuel, in the form of a fine spray, is injected into the inlet manifold where it combines with the air, drawn in by the engine.

The timing of the metering unit to the engine is set in accordance with the engine designers’ requirements.

The injector is not adjustable in service. However, there is only one fault likely to occur. Impurities in the fuel may become trapped on the valve seat, and thus prevent the nozzle valve from closing. These impurities can usually be removed by connecting the injector to a filtered air-supply, having a pressure of about 80 lbf/in2 (551.50 kN/m2) in the forward direction. If, however, the injector remains ‘stuck open”, it should be renewed.

 

Fig. 11

 

FAULT DIAGNOSIS: PRELIMINARY CHECKS

If the petrol injection system is suspected of not functioning correctly, the following preliminary checks should be carried out, as a failure in any of these would give the impression that the petrol injection system was faulty.

1. Battery
Check that the battery is at least 70% charged and in good condition. If the battery is not satisfactorily charged, re-charge from an external source, as necessary.  Note: A battery in poor condition will cause difficult starting.

2. Ignition System
Faults in the ignition system can often result in symptoms similar to those caused by a fault in the fuel system. Check both LT and HT circuits.

3. Petrol Tank Breather
The petrol tank breather must be inspected to ensure the tank can breathe properly. If air cannot enter the tank, a depression will be formed. Eventually no fuel will be drawn from the tank, and the engine will stop.

4. Back Leakage Return to Tank Pipe
If the back leakage pipe (return to the tank) is obstructed, a pressure build-up will occur on the cam follower seal. This will result in over-fuelling and in extreme conditions the seal will be unseated.

5. Engine Depression Check
Connect vacuum gauge into depression signal line, i.e. in the pipe line between (center pair) air intake manifold and the metering distributor vacuum connection. With engine running at ‘tick over’ speed (850 rev/mm) gauge should read: 7” Hg (180 mm Hg) for TR5/6, and 12” Hg (305 mm Hg) for 2.5 liter. If reading is low, reset tappets, synchronize throttle butterflies, and check ignition timing.

6. Fuel Supply
Finally, check that there is sufficient clean fuel in the petrol tank to supply the engine’s requirements. (The fuel pump should deliver at least 100 cc (100 ml) in 5 seconds.)

Fig. 12