The following preheater failures may occur on a KamAZ vehicle:

  • - the electric motor of the pumping unit does not work;
  • - fuel in the preheater boiler does not ignite.

Signs of the first failure: at any operating position of the switch lever, the electric motor circuit does not turn on and the electric motor cannot be heard.

Reason for rejection:

  • - turn off the fuse;
  • - switch failure; motor relay malfunction;
  • - broken wire between relay and motor;
  • - motor malfunction.

Signs of the second failure: lack of a uniform hum of fuel combustion and heater heating.

Reason for rejection:

  • there is no spark charge between the spark plug electrodes;
  • The electric fuel heating relay, electric fuel heater or fuel solenoid valve does not work.

Checking the batteries, battery switch and connecting wires to the fuse in the preheater system circuit

Checking is done with a test lamp by connecting it between the device under test and the car body.

If the lamp does not light when the lamp is connected to the input terminal of the fuse, then the batteries need to be checked.

Checking the fuse for 30 A current

Checking a 30A fuse

Voltage test on fuse wire 95

Press the safety button (fig. 1),

Then connect the lamp to the output terminal of the fuse (fig. 2).

In this case, the lamp should be on; if it does not light, then the fuse is defective

Checking the operating mode switch and connecting wires

Connect a test lamp to terminal 96 (red wire) of the operating mode switch.

The lamp should be on.

The health of the switch is checked with a test lamp.

To do this, the end of one wire is connected to the car body, the end of the other wire is connected in turn to the terminals of the operating mode switch.

When connecting to a terminal with a green wire, the switch must be in position II, when testing terminals with blue wires - in position 1 or II, when testing a terminal with a brown wire - in position 1;

Checking the connecting wires from the switch to the motor contactor and the contactor itself

Checking the contactor

To check the condition of the wires, the test lamp is connected in turn to the terminals of the contactor (Fig. 3).

To check the serviceability of the motor contactor, it is necessary to connect a test lamp to the output of the contactor 96 (white wire), and set the operating mode switch to position III.

The lamp should be on, if it is not on, then the contactor is faulty;

Checking the electric motor of the pumping unit and connecting wires to the contactor

The wire is checked by connecting a test lamp to the output of the electric motor. To check the operation of the electric motor, connect the “+” of the batteries to the output of the electric motor.

A healthy engine should work.

A control ammeter connected in series with the motor measures the current consumed by the motor. It should not exceed 13...14 A.

If the current is lower, check the condition of the commutator and motor brushes.

At a higher current value, the condition of the excitation winding and the armature winding is additionally checked.

Checking can also be done if you put the switch in position III and first check the condition of the wire.

Control is carried out by ear: if the engine is running, then the wire is working.

However, the failure of the electric motor can be caused not only by a malfunction in the electrical circuit, but also in the event of a jamming of the fan impeller or the impeller of the liquid pump, mounted on the armature shaft of the electric motor.

In this case, the armature will not rotate and the current in the electric motor circuit will be more than 30 A. In this case, the fuse will operate and turn off the entire circuit of the electrical devices of the preheater.

Checking the electric fuel heater relay and connecting wires from the motor contactor

To check the operation of the relay, it is necessary to connect a wire from the control lamps to terminal 100 (red wire) and turn the switch to position III.

The lamp should be on, if it is not on, you must connect a test lamp to terminal 98A (black wire) with the same switch position. If the lamp is on, then the relay is faulty, if it is off, the wire is faulty;

Checking the electric fuel heater and connecting wires from the heater relay

The wire is checked by connecting a test lamp to the output of the electric heater (the operating mode switch is in position III).

The lamp should be on. The health of the electric heater is checked by connecting a test lamp to its terminals.

The other wire from the lamp is connected to the battery.

The lamp will be lit if there is no electrical heater circuit failure.

You can measure the resistance of an electric heater or the current drawn by an electric heater. It should not exceed 8.5 A;

Checking the ignition coil, transistor switch and connecting wires

The wire from the ignition coil to the mode switch is checked with a test lamp, the output of which is connected to terminal 99 of the ignition coil (the mode switch is in position II).

The lamp should be on.

To check the transistor switch and the ignition coil, disconnect the high-voltage wire from the spark plug and bring its tip with a gap of 8 ... 10 mm to the car body.

Set the operating mode switch handle to position II and observe sparking.

No spark is a sign of a switch or ignition coil failure;

Checking the candle

Checking the spark plug

The candle is unscrewed from the boiler, and then a high-voltage wire from the switch is connected to it and sparking between the electrodes is checked (Fig. 4);

Checking the wire from the mode switch to the solenoid fuel valve and the valve itself

When checking the valve, set the switch to position 1. At this moment, a click of the electromagnet should be heard.