A Short Guide On Mercedes Sprinter Glow Plug Fixing
If your diesel Mercedes-Benz Sprinter starts slowly, will not start in the cold, blows white smoke or lacks power, check the glow plugs and the glow plug control module (relay). Test the circuit with a test light and an ohmmeter, clean fouled plugs with brake parts cleaner, and replace worn plugs. Plan on new glow plugs about every 60,000 miles (95,000 km).
Glow plugs are long metal tubular devices with an internal element that are put into the engine. An electrical connector is attached to the external top section of the glow plug, while the internal bottom section resides inside the engine, above the cylinder.
The glow plug heats up and the tip glows when a diesel engine is started, which is why they are called glow plugs. The glow plug's heat warms the air and fuel in the cylinder, allowing combustion to begin.
The glow plugs will be turned off once the diesel engine has started and warmed up. The length of time the glow plugs stay lit after the engine has started is determined by the glow plugs, the engine, and the ignition system. After 3 to 5 minutes, certain plugs may turn off.
You may need to wait for the glow plug to heat up before starting the engine in colder climates, and some vehicles may be equipped with air intake heaters to raise air temperatures, or you may not notice any delay in starting the diesel.
Glow plugs are long-lasting, but the more you use them, the faster they wear out, become damaged, and fail. A glow plug's life might also be shortened by carbon buildup or engine pollutants. When glow plugs fail, the car may take longer to start or not start at all, or it may misfire, resulting in smoke from the exhaust.
Glow plugs will ultimately need to be replaced due to wear and tear.
TL;DR
- Glow plugs heat the air and fuel in the cylinder so a cold diesel can start; some switch off 3 to 5 minutes after the start.
- Symptoms of failure: hard or no start in the cold, white smoke, low power, misfires, glow plug light on the dash.
- Test: power at each plug with a test light; a working relay reads 50 to 120 ohms, below 50 ohms it is suspect.
- Clean fouled plugs with brake parts cleaner; replace worn ones about every 60,000 miles (95,000 km).
- Disconnect the 12-volt battery negative cable before you remove any glow plug.
- If this is not your case, read the Sprinter DPF clogged guide.
Table Of Content
- What happens when you start a diesel Mercedes-Benz Sprinter?
- What are the signs that a glow plug control module in Mercedes-Benz Sprinter is faulty?
- How do you test and fix the glow plug system in a Sprinter?
- How do you clean glow plugs in a Sprinter diesel?
- How to replace Mercedes-Benz glow plugs: A step-by-step guide
- When should your glow plug control module be replaced?
- Conclusion
What Happens When You Start A Diesel Mercedes-Benz Sprinter?
- Based on information from the Engine Control Unit, the glow plug control module determines the timing and electric current required by the glow plugs.
- The glow plug's heating element is electrified, which causes it to heat up and emit visible light (thus the name).
- The air that enters the system is compressed.
- The fuel injector spray directs fuel to the glow plug's hot tip.
- Even when the engine is cold, the injected diesel mixes with the compressed air evaporates and begins burning practically instantly.
- The glow plug stays on during the pre-heating phase to ensure proper fuel combustion and minimise your car's environmental effect.
The increase in temperature of the intake air during compression, as well as the relatively low ignition temperature of diesel, aid this process. However, a glow plug control module is still required since, without it, the compression temperature of a cold diesel engine may not be high enough to assure effective ignition of the injected fuel. As a result, exhaust emissions would rise.
What Are The Signs That A Glow Plug Control Module In Mercedes-Benz Sprinter Is Faulty?
The glow plugs in a diesel engine are controlled by a single glow plug control module. This implies that if a single glow plug fails, you may not notice because it only affects one cylinder in your engine. However, if two of the three fail or the control module itself fails, starting the engine will become increasingly difficult. Here are some frequent indications of a malfunctioning glow plug or glow plug control module, in addition to looking for the glow plug light on your dashboard:
| Symptom | Likely cause | What to check |
|---|---|---|
| White smoke from the exhaust | Faulty glow plug lets unburnt diesel reach the exhaust | Test each plug, replace the bad one |
| Hard start, or no start in cold weather | Two or more failed plugs or a failed control module | Glow plug circuit, then fuel system and batteries |
| Low power after a hard start | Inefficient combustion | Plugs and relay resistance (50 to 120 ohms) |
| Rough running, black smoke, no pick-up | Glow plug system fault | Follow the test steps below |
White Smoke Emanates From Exhaust
Diesel will seep into the exhaust system and burn due to a faulty glow plug.
Engine Becomes Difficult To Start
This could indicate that the engine starts slowly in hot weather or does not start at all in cold weather. This, however, could be a sign of a problem with the fuel system or the batteries; see the auxiliary battery malfunction guide if the battery warning is also on.
Engine Power Is Insufficient
Due to inefficient combustion, which affects power and efficiency, defective glow plugs will make it difficult for your automobile to function effectively after a tough start.
How Do You Test And Fix The Glow Plug System In A Sprinter?
In a diesel engine, glow plugs pre-heat the injection chamber, making it easier to start. The pre-heat cycle of the glow plug system is controlled by the glow plug relay, which is based on the reading from the cylinder head's temperature sensor. If your Mercedes-Benz Sprinter is running rough and has no pick-up, or if black smoke is spewing out the back, check for glow plug problems.
1st Step
Determine which sections of the glow plug system are simple to reach. Begin with the easiest and work your way up to the most difficult. This procedure will assist in determining the logical sequence in which the various components of the glow plug system should be tested.
2nd Step
Locate the glow plug temperature relay's wire. Reconnect the wire if it's been disconnected.
3rd Step
Connect a test light to the glow plugs to see if they are getting the power they need. The plug is receiving electricity if the test light illuminates.
4th Step
Test the ohms of the circuit with an ohmmeter to see if the relay is capable of supplying the power required to start the diesel engine. A functional relay will have a resistance of 50 to 120 ohms. The relay is questionable if the circuit produces less than 50 ohms.
5th Step
To test each pin for voltage and/or power, use a relay socket:
| Relay pin | What it must show |
|---|---|
| 30 | Battery voltage |
| 50 | Power when the engine is running |
| 85 | Battery voltage |
| 86 | Power when the key is turned to the pre-glow position |
| 87 | Direct power to the plugs |
| L | Power sent to the dashboard LED |
| T | Input from the cylinder head temperature sender |
The relay is not working properly if any of these pins are not receiving or delivering voltage and/or power. A scan tool helps here too; the OBD2 troubleshooting guide explains how to read the codes.
6th Step
Check the fusible link for any loose wires or nuts, as well as unclean contacts.
Connect the glow plug to the dashboard LED with a wire. The relay is defective if you hear clicking and watch the light turn on and off but there is no electricity reaching the glow socket.
How Do You Clean Glow Plugs In A Sprinter Diesel?
Diesel engines are naturally dirtier than conventional gasoline engines. Diesel fuel has a lower refinement level than gasoline. Impurities in the gasoline may form as a result of this. An oil leak in the engine might also cause the glow plugs to foul. Furthermore, carbon buildup from the plug's typical heat cycle might cause it to get dirty. The glow plugs will need to be cleaned if this happens.
1st Step
Disconnect the glow plug wire from the engine. Although you will be cleaning all of the plugs, you should begin by cleaning one plug at a time. Remove the top of the plug wire from the engine. You may need to carefully twist the plug wire back and forth as you draw it up, but it should come out easily.
2nd Step
Lower the glow plug socket into the plug well after attaching it to the socket extension.
3rd Step
Place the wrench in such a way that the socket clutches the top of the plug.
4th Step
To remove the socket (and plug), use a socket wrench to turn it counterclockwise.
5th Step
Examine the electrode on the plug's bottom to ensure it is not damaged. Remove the plug from its socket and thoroughly clean it with brake parts cleaning. This will clear any loose carbon deposits or oil from the plug's bottom. Allow the plug to dry naturally.
6th Step
Reinstall the glow plug, tighten it, and attach the plug wire over it.
For each glow plug, repeat steps 1 through 6.
How To Replace Mercedes-Benz Glow Plugs: A Step-by-Step Guide
What Tools Do You Need to Replace Your Glow Plugs?
Checking the condition of your glow plugs regularly and replacing them as needed can maintain your engine in great shape. To replace your glow plugs, you'll need the following items:
- Torque wrenches, socket wrenches, and ratchets are all the necessary manual tools.
- Pliers
- Screwdriver
- Reamer for glow plugs
- Glow plugs that have been replaced
Glow Plug Replacement In 7 Easy Steps
1st Step: The Battery Cable Must Be Disconnected
Disconnect the black negative battery cable by opening the bonnet. Because glow plugs draw the entire 12 volts from the battery, this is an important safety measure. To release the nut that links the cable to the negative terminal, you may require a wrench.
2nd Step: Remove The Valve Cover From The Glow Plugs
You'll need to remove the valve cover if your glow plugs are protected by one. Remove the retaining screws around the outside edge of the cover and inspect it for damage before replacing it.
3rd Step: Remove The Valve Cover From The Valve
The glow plug wires must be disconnected. The glow plugs are located in the cylinder head and are connected to a wire that supplies the 12-volt power source. Nuts, bolts, terminals, or other similar connection devices will be used to connect the wires to the plugs.
When removing tight terminals, pliers can be useful.
4th Step: Glow Plug Wires Should Be Removed
The glow plug wires must be disconnected. The glow plugs are located in the cylinder head and are connected to a wire that supplies the 12-volt power source. Nuts, bolts, terminals, or other similar connection devices will be used to connect the wires to the plugs.
When removing tight terminals, pliers can be useful.
5th Step: Glow Plugs Should Be Removed
Using a socket and a ratchet, remove the glow plugs. Place the ratchet over each plug and rotate it counterclockwise. To loosen the plugs, you may need to attach a deep well socket to the socket wrench.
You'll be able to assess the condition of each glow plug after you've removed it. Glow plugs can break down once installed, so make sure you get all the components out of the engine before removing a broken one.
6th Step: Put The New Glow Plugs In Place
Install the new glow plugs by hand, placing them and tightening them with a wrench in a clockwise motion. Overtightening the plugs might cause them to shatter, so be careful.
7th Step: Connect The Cables Again
Reconnect the glow plug wires, securing the nuts, bolts, or terminals with a tool.
Reinstall the valve cover. You can read your Mercedes-Benz Sprinter owner's manual to see whether the valve sockets need to be torqued to a certain pressure.
To test your new glow plugs, connect the battery cable and start your engine. You can also test your plugs with a scan tool.
When Should Your Glow Plug Control Module Be Replaced?
Changing your glow plugs or glow plug control module is a simple task that should be done every 60,000 miles (95,000 km). This helps you avoid finding out they have failed on a freezing morning. For other cold-start problems, read the cold weather starting guide.
Before you begin, make sure you have read all relevant instructions in your owner's manual and that you have all the necessary tools.
Conclusion
Because diesel engines lack spark plugs or any type of ignition system, it is up to the glow plugs to start the engine when it is cold or outside. Diesel glow plugs have a long service life, but they still wear and must be replaced regularly.
Mercedes Sprinter Problems-