F8Q 620 engine
The system consists of glow plugs screwed into swirl chambers, a control unit mounted on a bulkhead in the engine compartment, and a coolant temperature sensor attached to the thermostat housing.
The glow plugs are powered by the control unit, which is also controlled by the fast idle solenoid valve (on models with air conditioning) and exhaust gas recirculation valve (refer to accompanying illustration).
If preheating is necessary, it starts at the moment the ignition is turned on and partially continues until the engine is completely warmed up as follows.
When the ignition is switched on, the control lamp on the instrument panel lights up and power is supplied to the glow plugs, depending on the temperature of the coolant. (If the coolant temperature sensor is defective, the spark plugs are automatically energized for 14 seconds). In the second phase, after the warning lamp goes out, the glow plugs continue to receive power for another 8 seconds or until the engine starts. The glow plugs are powered continuously while the starter is running.
After starting the engine, all glow plugs are energized for another 10 seconds. Further, the power supply depends on the temperature of the coolant and the engine load. Glow temporarily stops if the control unit receives a signal "ultimate load" from the microswitch on the fuel pump and restarts if the microswitch contacts open again. The glow is turned off completely when the coolant temperature reaches 65°C, or after 30 seconds if the coolant temperature sensor is defective.
F8Q engines with turbocharger
The preheat system is controlled by the same ECU that controls injection timing, fast idle and EGR. The unit controls the glow plug relay and is located in the engine compartment.
When the ignition is turned on, the control lamp on the instrument panel lights up and energizes the glow plugs, depending on the temperature of the coolant and the altitude above sea level (the control unit contains a height sensor). After turning off the warning lamp, the glow plugs continue to be energized for another 8 seconds, or until the engine starts. The glow plugs are powered continuously while the starter is running.
After starting the engine, all glow plugs are energized for another 10 seconds. Further, the power supply depends on the temperature of the coolant, engine speed and load. Glow temporarily stops if the control unit receives a signal "ultimate load" from the throttle lever potentiometer on the fuel pump; and resumes if the load decreases again. The glow is turned off completely when the coolant temperature reaches 65°C, or after 190 seconds.
F9Q engines
The preheating system is controlled by the injection ECU, located in the right front of the engine compartment, near the fuel filter.
When the ignition is switched on, the control lamp on the instrument panel lights up and power is supplied to the glow plugs, depending on the temperature of the coolant. (If the coolant temperature sensor is defective, the spark plugs are automatically energized for 14 seconds. After the warning lamp goes out, the glow plugs continue to receive power for another 8 seconds, or until the engine starts. The glow plugs are powered continuously while the starter is running, but not longer than 20 seconds and while the coolant temperature is below 60°C.
After starting the engine, all glow plugs are energized depending on the coolant temperature and engine speed. Glow stops temporarily if the engine speed exceeds 2500 rpm, and completely if the coolant temperature exceeds a certain value.
Examination
1. When a fault occurs in the system, the health check is ultimately limited to swapping with known-good units, but some preliminary checks can be done as follows.
2. Connect a 12V voltmeter or test light between the glow plug power cable and ground (car engine or body).
3. Have an assistant turn on the ignition and check that power is being supplied to the glow plugs. Note the amount of time the pilot lamp will stay on and the total amount of time power is applied before shutting down the system. Switch off the ignition.
4. At a temperature in the engine compartment of 20°C, the average time should be as follows: the control lamp should burn for 5-6 seconds, and after it goes out, the power to the candles should be supplied for another 4-5 seconds (if the starter is not engaged). The control lamp will burn longer at a lower temperature, and vice versa.
5. If there is no power at all, the relay or associated wiring is faulty.
6. To identify a defective glow plug, disconnect the power cable and attach a piece of wire to the center clamp of the glow plug. Be careful not to drop nuts and washers.
7. Check the resistance between each glow plug terminal and ground. Good glow plug resistance is very low (less than 1 ohm), and if the tester shows high resistance, the glow plug needs to be replaced.
8. If an ammeter is available, the current drawn by each glow plug can be measured. After an initial surge of up to 15-20A, the spark plug should draw about 10A of current. If the spark plug draws much less current, it is probably defective.
9. For a final check, the glow plugs can be removed and inspected as described in Section Removal, inspection and installation of glow plugs.
F8Q 620 engine
Preheat control unit - engine F8Q 620
Connector A + battery: constant power
Connector B
1 - Feeding glow plugs 1 and 3
2 - Feeding glow plugs 2 and 4
Connector C
A1 / S2 - Solenoid valve boost control
A2 / PC - Signal from the microswitch on the gas lever
A3 / CTN - Signal from the coolant temperature sensor
B 1 / + APC - Ignition-controlled positive power
B2 / DEM - Starter signal
B3 / Tem - Control of the heating control lamp (through the earth)
C1 / S1 - Not used
C2/-Bat - Weight
C3 / Clim - The mechanism for controlling the solenoid valve for fast idle speed during preheating
1. If a malfunction of the control unit is suspected, then the next steps depend on which of the following symptoms are present:
- a) The control lamp of a glow on the instrument panel does not work.
- b) The control lamp of a glow is lit for a short time.
- With) Lack of fast idle mode when the engine is not warmed up (models with air conditioning).
- d) Engine fails (it is difficult to start from a cold state, it is unstable after starting.
2. If the glow plug is not on, disconnect the connector "WITH" control unit. Close the connector of the test lamp (contact B3/Tem) to ground using a 2A fuse (refer to illustration above). Turn on the ignition. If the fuse blows, there is a short circuit in the control lamp wiring in the instrument panel and must be repaired. If the fuse does not blow, but the lamp does not light up, then the lamp itself has burned out, or its wiring is defective.
3. Then check the battery positive power supply (+BAT) on connector "A", ignition control feed (В1/+Ars) on connector "WITH" and battery ground (C2/-Bat) on connector "WITH". If everything is in order, but the problem persists, replace the preheat control unit.
4. If the filament control lamp lights up briefly only at the moment of switching on, disconnect the connector "IN" and turn on the ignition again. If the test lamp now lights up and voltage is present at the connector outputs "IN", check the glow plug circuit (refer to paragraphs above). If no fault is found in the circuit, check the glow plugs (refer to section Removal, inspection and installation of glow plugs). If the test lamp lights up, but at the connector outputs "IN" there is no voltage, replace the preheat control unit. If the test light only comes on for seconds, check the battery positive power supply at the connector "A".
5. If there is no fast idle when the engine is cold, turn on the air conditioner. If fast idle is now working, check the connector "WITH" preheat control unit. Check that there is no break in the wiring between pin C3/Clim of the connector "WITH" and pin 1 of the solenoid valve connector. If there is no open, replace the preheat control unit (make sure the indicator lamp is working). If the fast idle mode does not turn on even when the fast idle valve is activated, repair the circuit between the vacuum pump, solenoid valve and vacuum motor. If the valve does not open, check the voltage between the two pins of its connector. If there is a voltage of 12V, replace the solenoid valve after checking the condition of the connector. If there is no voltage, check the continuity between pin 2 of the valve connector and ground.
6. If the engine fails (hard to start, rough idle, etc.), check the main power circuit of the preheat control unit (connector "A"), ignition-controlled positive power supply (connector "WITH") and ground on pin C2/-Bat of the connector "WITH". Also check the current in the fuel pump connector.
7. Check the resistance of the coolant temperature sensor (talk to Specifications). Check the adjustment and function of the preheat microswitch (refer to section Adjustment, check, removal and installation of the glow microswitch).
8. If the engine still fails after these checks, contact a diesel engine specialist.
Turbocharged F8Q and F9Q engines
1 To check the heating system, a special device is required (Renault XR25), which is included in the diagnostic clutch. With this tool, you can quickly and easily locate a fault in the system by reading the fault codes stored in the computer's memory.