Purpose, device and action of EFU

The device is designed to make it easier to start a cold engine at air temperatures down to -25 °C, quickly return the engine to normal temperature conditions and reduce smoke that occurs in an unheated engine.

The EFU glow plugs are screwed into the threaded holes of the intake manifolds.

The EFU solenoid valve is installed on the engine, the thermal relay is on the cab panel from the inside.

The EFU enable relay is located on the panel

The relay for switching on the EFU is located on the front panel of the cab on the right side in the direction of the vehicle (see Fig. 1).

KamAZ efu candle

The heater switch-on relay and the EFU switch-on contactor are in the cab behind the fuse panel.

When the engine is started, the fuel priming pump delivers fuel through the fine filter to the spark plugs.

The bypass valve of the high-pressure fuel pump and the jet valve of the fine fuel filter are closed, and fuel under pressure enters the EFU spark plugs with a minimum delay from the moment the solenoid valve opens.

At a pressure greater than 25…45 kPa (0.25…0.45 kgf/cm2), the jet valve opens, maintaining the optimum pressure in front of the EFU spark plug jet for stable flame burning.

The electrical circuit of the EFU system consists of a power button, a candle switch relay, a thermal relay, an electromagnetic fuel valve, two pin candles, and a control lamp.

The electric torch device works as follows: when the candle button is turned on, the voltage from the batteries through the ammeter, relay and thermal relay is supplied to the EFU, pin candles. At the same time, they are heated.

Simultaneously with the heating of the candles, the thermal relay heats up and activates, including the electromagnetic fuel valve and the control lamp of the unit.

In this case, the valve opens access to the candles, and the ignition of the control lamp indicates the readiness of the device to start the engine.

In addition, when the plug button is turned on, voltage is applied to the relay, which breaks the circuit of the generator excitation winding, which is necessary to protect the plugs from the voltage generated by the generator when the engine reaches a stable mode accompanied by the operation of the EFU.

The current consumed by the electric torch device does not exceed 24 A. This value of the current consumed does not adversely affect the subsequent starter discharge of the batteries.

The resistance of the thermal relay coil is chosen in such a way that a voltage of 19 V is provided at the terminals of the candles (the nominal voltage of the candles).

When the engine is started, the thermal relay is bypassed, i.e. voltage is applied to the candle terminals bypassing the thermal relay coil, since when the engine crankshaft is turned by the starter, the voltage at the battery terminals decreases.

Figure 3 shows a functional diagram of starting the engine of cars of the KamAZ family.


The EFU power button is checked with a test lamp

The operation of the EFU should be checked with good and charged batteries in the following order:

  • - check the operation of the EFU signaling device on the instrument panel in the cab (by pressing the control button);
  • - turn on the EFU and determine the time of the moment when the EFU is turned on before the signaling device lights up.

For the first inclusion of the EFU, it should be 50-70 s at an air temperature above zero, and 70-110 s at a temperature below zero.

When the EFU is turned on again, the signaling device ignition time is reduced, therefore, in order to obtain a reliable value, it is necessary to allow the thermostat to cool down to the ambient temperature:

  • - check for the presence of a torch flame in the intake manifolds.

To check the torch you need:

  • - unscrew the spark plugs from the collectors, connect fuel pipes and electrical wires to them;
  • - ensure a reliable connection of the candle bodies to the mass and make sure that the terminal is isolated from the mass;
  • - turn on the EFU, and after the indicator lights up, use the starter to turn the crankshaft. If there is no flame, then replace faulty spark plug.

Assembling a circuit to test the EFU thermal relay

Determine the performance of relay 4 for switching on the EFU in the following order:

  • - disconnect any wire from the output "K" of the additional starter relay;
  • - press the EFU power button and two or three times for no more than 1s, turn the instrument and starter switch key to position II (rightmost position). With a working relay, characteristic clicks should be heard;
  • - turn off the EFU and connect the wire to the "K" terminal.

Determine the performance of the OVG shutdown relay as follows:

  • - press the EFU button and start the engine with a starter. The ammeter needle, when changing the engine speed over the entire range, should show a discharge current of about 30 A. Stop the engine and only then release the EFU button;
  • - Start the engine again and make sure the alternator is charging.

ESF failures

Voltmeter pointer at the bottom of the scale:

  • - Closing the spiral of a thermal switch or electric wires
  • - Closing the spark plug to ground - If the spark plugs are good, disconnect the wire from the thermal relay that connects it to the EFU power button.

The absence of a change in the readings of the arrow indicates the closure of the thermal relay coil. In this case, the thermostat should be replaced.

If the thermal relay spiral is intact (determined by touch) and the position of the arrow does not change when the wires are disconnected from the candles, then this indicates a short circuit in the electrical wires.

Remove the closure.

Disconnect the wire from the output of the left candle, eliminating the contact of the tip with the ground, and turn on the EFU again.

When the arrow goes beyond the scale, disconnect the wire from the output of the right candle.

The absence of the arrow going beyond the scale indicates the closure of the right candle.

Replace the failed spark plug.

After the short circuit is eliminated, it is recommended to check the condition of the insulation of the electrical wires, the operability of the thermal relay and the EFU switch-on relay, and if the short circuit occurred when the engine was started, the operability of the shunt relay

Voltmeter reading does not change:

Burnout of the thermal relay coil - Turn on the EFU and check the voltage at the thermal relay terminals.

The absence of voltage at the terminal on the side of the plug connection, while there is voltage at the other terminal, indicates a burned out spiral.

Replace thermostat

Spark plugs burned out or no contact in the circuit - Turn on the EFU and check for voltage at the terminals of each EFU product, starting with torch candles.

The presence of voltage at the output of the right candle indicates a burnout of the candles.

Replace spark plug and reconnect

Burnout of one of the candles - Turn on the EFU for 10-15 seconds, then replace the cold candle

No candle torch:

Lack of fuel supply to the spark plug - Loosen the fuel supply fitting on the spark plug.

Turn on the EFU and, after the signaling device lights up (opening the solenoid valve), turn the crankshaft using the starter.

If the fuel does not seep through the loose fitting screw connection when the valve is open, troubleshoot the fuel supply system

Fuel not passing through the spark plug - Unscrew the spark plug from the manifold.

Rinse and blow out the jet, fuel filter and fuel cavities with compressed air.

Check for torch flame

Leak in the fuel supply system - Repair the leak

Signs of device failure may include:

  • scaling of the ammeter needle;
  • ammeter needle does not deviate;
  • The ammeter needle shows half the discharge current; no flame torch.

The most typical failures include:

  • short circuit of the candles to ground; short circuit or burnout of the thermal relay coil;
  • burnout of candles or lack of contact in the circuit;
  • Fuel system failure.

The EFU power button is checked using a test lamp by connecting it to the terminals in turn (Fig. 4).

When the lamp is connected to terminal 15, the lamp should be on, when connected to terminals 19 and 17, the lamp should not be on (when the EFU power button is released).

When the button is pressed, the voltage should be on all three pins.

The ammeter is checked in the same way.

To check the EFU thermal relay, connect a test lamp to terminal 19: the lamp should be on.

Then they check the health of the thermal relay winding by connecting the lamp to terminal 17A or 17B (Fig. 5): the lamp should be on (the EFU power button is pressed).

To check the health of the thermal relay contacts, you must connect the lamp to terminal 18 (or 19A), press the EFU power button. A working relay should turn on the lamp after 75 ... 110 s.

To test the EF relay You need to connect a test lamp to the output 17B of the EFU relay (the EFU switch button is pressed).

The lamp should be on, if it is not on, then the wire is faulty.

Then they check the health of the relay contacts, for which they connect the lamp to terminal 17A (the EFU power button is pressed): the lamp should be on.

To test the fuel solenoid valve, the wire from the "+" batteries must be connected to the valve terminal. At the same time, a click of the valve operation should be heard.

To check the torch candles, unscrew the candles, install them on the car body and turn on the EFU button. After 75...110 seconds, the candles should glow.


The products of the electric torch device are not subject to repair; if a product failure is found, replace it.

To check the fuel supply to the spark plugs, disconnect the fuel line from the spark plug and bleed the engine supply system with fuel with a manual fuel priming pump.

Next, open the electric valve by applying voltage to the valve plug from the plug of the engine compartment lamp wire. In this case, fuel should appear from the disconnected fuel line.

Installation diagram for testing the throughput of EFU candles

Determine the capacity of the candle on domestic stands SDTA-Z (KI-22201) and others, which allow you to smoothly adjust the fuel pressure.

At an overpressure of diesel fuel of 73.6 kPa (0.75 kgf / cm2) and a temperature of 15 ... 25 ° С, the throughput of the candle should be 5.5 ... 6, 5 cm3/min.

Measurement is carried out after preliminary filling of the spark plug with fuel for 20...30 s.

In the absence of the indicated stands, assemble the installation according to the diagram in fig. 6.

Scheme for checking the current consumed by a spark plug

To determine the amount of current consumed by a candle, assemble a circuit (Fig. 7) that allows you to have a DC output voltage of 19 V.

Maintain the voltage with a rheostat 2. At this voltage, the current consumed in a minute after turning on the candle should be 11 ... 11.8 A.

Checking scheme for EFU thermal relay

To check the parameters of the thermal relay, assemble the circuit shown in fig. 8. Install the thermostat on a horizontal surface with the protective screen up.

Set and maintain the rated current of 22.8 A through the relay with rheostat 2.

Determine the time until the contacts close and hold them in the closed state by lighting up the control lamp 4.

To do this, connect one wire of the control lamp to the thermostat plug, and the second to a DC source (battery).

The time from the moment the current is turned on to the closing of the thermal relay contacts (lighting of the control lamp) at an ambient temperature of 15 ... 25 ° C should be 55 ... less than 45 s.

Check the tightness of the solenoid valve by supplying compressed air at a pressure of 147 kPa (1.5 kgf/cm2) to the valve inlet.

When the valve is immersed in water, no air bubbles should be released.