Lucas MK1 and MK2 fuel / petrol injection



Lucas Service Training Centre
Petrol Injection Mk II

Fuel Pump Not Operating
- Electrical Check (in-situ)

If the engine fails to start, or is difficult to start, check that the fuel pump is operating satisfactorily. When the ignition is switched “on”, the fuel pump should start operating. (This is confirmed by hearing the note of the driving motor, or by feeling the slight vibrations in the body of the pump).

If the pump is not operating, connect a voltmeter across these cables, on the supply side, and an ammeter in one of the leads. When the ignition is switched on, the voltmeter reading should be 12 volts and the ammeter should read approximately 5 amperes, see Figure 15.

If the voltmeter reading is zero, one of the leads to
the motor is open-circuit.

Low readings (for both voltage and current) indicate a high resistance in the circuit. The wiring to the motor should, therefore, be checked.

Any other variations in voltage and current readings indicate a faulty pump motor; possibly a defective brush assembly or open-circuit armature winding. Remove unit for further examination.

A high reading indicates a tight pump or stalled motor or short-circuited armature windings. Remove for further examination.


Fig. 15



Fuel Pump Operating - Feed-line Check (in-situ)
If the engine fails to start, or is difficult to start, but the fuel pump operates when the ignition is switched on, the ignition system should be disconnected. This is effected by disconnecting one of the LI cables at the ignition coil. The ignition switch is left in the “on” position. The engine is cranked by operating the starting motor. Each feed-line is gripped lightly in turn, and the pulsations are noted, see Figure 16.

If the feed-lines are tied together, they should
be separated to avoid the misleading effects of “reflected pulsations”.

This test will show either:
(i) that there are strong pulsations in all feed-lines.
or (ii) that there are no pulsations in any feed-line.

i) Strong Pulsations in All Feed Lines
These indicate that the petrol injection system is operating satisfactorily, and is unlikely to be the cause of engine failure.

(ii) No Pulsations in Any Feed-Line
If there are no pulsations in any feed-line, the fuel pressure should be checked. Insert a pressure gauge in the supply line (see Figure 17). Switch ignition on and note reading on pressure gauge, which should be within the limits 100-110 lbf/in2 (689.50-758.50 kN/m2).

To adjust, if necessary, switch off ignition and with a screwdriver inserted in the slot of the relief valve turn
to adjust the fuel pressure. Switch on ignition and
again note pressure reading. Repeat this operation
until fuel pressure is within required limits.


Fig. 16

Fig. 17

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