Direct injection engines have significantly shorter warm-up times.
In addition, this device serves mainly to reduce the toxicity of exhaust gases.
Operation of the preheater
The preheating device consists of three main components: a glow plug, a preheating time switch and a warning lamp on the instrument panel.
The glow plugs are rated for 15 V and connected in parallel. When the ignition key is turned, a current of about 30 A flows through each candle. The control winding in the glow plug reduces the current for about 10 seconds to 8-15 A. After 10 seconds of operation, the candles reach a temperature of + 900°C, after 30 seconds - + 1180°WITH.
The preheating time relay determines the duration of the preheating. To do this, the relay has a sensor that measures the ambient temperature. At -30°С, the preheating time is about 25 s, at +20°С - about 4 s, at +40°С - about 2 s. If the preheating is sufficient, the engine readiness indicator lamp goes out. If, after the lamp has gone out, the engine does not start, then the fuse ensures that after 20-25 seconds the current flowing through the candles is turned off. If the engine starts during this time, the preheating device is connected again during the rotation of the starter.
Glow plugs
Pic. 4.92. Glow plugs Bosch-Duraterm
This «quick start glow plugs» (pic. 4.92). In the incandescent rod, which enters the prechamber, the heating and control windings are located one after the other. As the temperature rises, the winding resistance increases. This reduces the current from 30A to 8-12A. Each glow plug is individually controlled by a microprocessor preheat timer. Additionally, during operation, the candles are fed with a small control current. Failure of one or more spark plugs with the engine running is signaled by a warning lamp. When the engine is started, additional heating begins - it lasts up to 180 seconds until the temperature of the coolant reaches +40°C. The point of additional heating is to reduce the loud start-up noise and improve exhaust emissions in a cold car. If the temperature sensor on the cylinder head is defective, then the post-heating lasts generally 30 seconds.
At high temperatures, the action of which candles are constantly exposed, they can fail. This is especially affected by incorrect nozzle spray, too low injection pressure or incorrect injection timing.
Preheating time relay
Pic. 4.93. Preheating time relay
This relay is installed in the engine near the left wing arch. If you remove the lining, then both nests are visible. Prestart time relay (pic. 4.93) heating performs the following functions:
- 1. The power relay regulates the incandescent current.
- 2. Limitation of the amount of supplied current through the use of an automatic fuse.
- 3. Turn off the warning lamp when the engine is ready to start.
- 4. The fuse cuts off the glow current if the heating remains on for 20–50 s (depending on ambient temperature).
Faulty preheating system
Malfunctions of the preheating system for CDI models can only occur when it is cold (below -10°С). Only then is it difficult for the direct injection system to cope with starting the engine without «support» heating systems. A system malfunction can be identified by blue exhaust from the muffler.
A malfunction in the preheating system is indicated by the fact that the control lamp does not light up when the ignition is turned on.
Malfunctions of the preheating system
If a cold engine does not start or starts very poorly, or when the ignition is turned on, the preheating system warning lamp does not light up on the instrument panel, the malfunction should be located and repaired. Start the search with a test lamp or by creating jumpers on certain electrical circuits. Various checks start at both sockets on the preheat time switch, which are easy to find by removing the cover.
If the control lamp does not light up when the heating is turned on, then there may be the following malfunctions.
- 1. No current on the terminal «30» preheating timer.
- 2. Faulty power relay.
- 3. Faulty one or more wires on glow plugs.
- 4. One or more glow plugs burned out.
- 5. The control lamp burned out or its connecting wire is damaged.
Failure of a control lamp
If the test lamp does not light up despite the fact that the engine starts well, then it may have burned out.
Pic. 4.94. Checking the operation of the control lamp of the preheating device: 1 - preheating time relay; 2 - plug of temperature sensor and control lamp; 3 - control lamp; 4 - plug of glow plugs; 5 - terminal for connecting a control lamp «to ground»
1. Pull out the small plug on the preheating time switch 1 (pic. 4.94).
2. Turn on the ignition.
3. Nest «3» plug connect with «weight». Now the control lamp should light up.
4. If not, check the wiring to the dashboard or replace the lamp.
Voltage control on the preheating time relay
If the engine does not start and the preheat indicator lamp does not come on, check the power to the preheat time relay.
1. The red wire must always be energized (terminal 30).
2. With the ignition on, the terminal «15» it should be «+». Check socket 1 on the smaller plug.
3. When the starter rotates, then on the terminal «50» there must also be a current (nest 2).
Checking the current supply to the glow plugs
After switching on the ignition, current must be supplied to all glow plugs.
1. Disconnect the large plug on the preheat time switch.
2. Connect a test lamp to «mass».
3. Check the current one by one on all relay contacts. After the ignition is turned on, each contract must have «+».
When checking, the assistant must constantly turn the ignition on and off so that the pre-glow mode is always on.
If there is no current from the relay, replace the relay.
Glow plug failure
If the control lamp does not light up, one of the glow plugs may have burned out. If the engine starts, at first it does not work on all cylinders. In a cylinder without preheating, self-ignition will occur somewhat later.
1. To detect a burnt candle, disconnect the large plug from the time switch.
Pic. 4.95. Faulty spark plug detection: 1 – «weight»; 2 – the terminal of a control lamp; 3 - socket in the plug
2. Connect a control lamp with one end to «+» (for example, to the red wire) (pic. 4.95).
3. With the other end of the lamp, one by one, check the sockets in the plug.
4. Where the control lamp does not light up, the glow plug is faulty.
Faulty spark plugs
1. If there is no test lamp to check, you can check the candle for «spark».
2. Remove the power plug from the preheat time switch and the wire from «+» check the nests one by one. Where there is no spark, the candle is faulty.
3. If the pre-heating system does not work, you can start the engine in tow. The engine can start after 1 km. Try starting in tow at higher engine speeds, for example in 2nd gear from 40 km/h (do it carefully!).
4. If the time relay is turned off while driving, stop, connect all wires to the candles together and connect for 10–20 s to «+».
Replacing glow plugs
1. To get to the glow plugs, which are located on the left side of the cylinder head, you need a key - «ratchet» with various nozzle heads.
Pic. 4.96. Glow Plug Location: 1 - glow plug with a plug; 2 – fuel line lock on the heat exchanger; 3 - heat exchanger; 4 - nozzle
2. Remove the protective cap on the candle (pic. 4.96).
3. Remove the spark plug.
4. Install a new spark plug and tighten to 20 Nm.
Checking glow plugs
The only and most reliable way to check the glow plugs is in the reversed state.
1. If necessary, remove the engine cover.
2. Disconnect the wires from the glow plugs.
3. Remove the candles and place them on a fireproof surface.
4. Connect the candles one by one with a thick wire (minimum 2.5 mm2) and reliable terminals directly to the battery.
5. Check which candles are weak (there are those too), and which do not sparkle at all.
6. Replace faulty spark plugs. If you want to be absolutely sure that the candles work, you can replace the entire set.