Troubleshooting Glow Plug Issues in Bobcat 873

[MikePhua]

Glow plugs play an essential role in the starting system of diesel engines, especially in colder climates. They help to preheat the air inside the cylinder to ensure a smooth and easy engine start. A malfunctioning glow plug system can lead to hard starts, excessive cranking, or even complete failure to start the machine. In this article, we will dive into the common causes of glow plug issues in the Bobcat 873 skid steer loader and provide detailed steps on how to troubleshoot and resolve the problem.
Understanding the Role of Glow Plugs
Glow plugs are electrically heated elements that are installed in the combustion chambers of diesel engines. Their primary purpose is to assist in starting the engine, especially during cold weather when the engine’s air-fuel mixture needs additional heat to ignite. The glow plug heats up, warming the combustion chamber, allowing the diesel fuel to burn more efficiently.
In the Bobcat 873, like many other diesel-powered machines, the glow plug system is activated when the engine is turned to the "start" position. Once the engine reaches a certain temperature, the glow plugs automatically turn off, but if any component fails, it can prevent the engine from starting properly.
Common Symptoms of Glow Plug Issues
When there’s a problem with the glow plug system in the Bobcat 873, you may notice the following symptoms:

1. Hard Starting
   The most obvious sign of a glow plug issue is difficulty starting the engine, particularly during cold weather. If the glow plugs are not working correctly, the engine will struggle to start, requiring more cranks or, in some cases, not starting at all.
   
2. Excessive Cranking Time
   If the glow plugs are only partially functioning, you may notice that the engine takes longer to start. While it might eventually fire up, it will require more cranking time than usual.
   
3. Smoky Exhaust During Start-Up
   Incomplete combustion due to insufficient preheating from the glow plugs can result in excessive smoke during the initial engine startup. If you see a cloud of smoke from the exhaust when starting, this is often a sign of glow plug failure.
   
4. No Start Condition
   If the glow plug system fails entirely, the engine may not start at all. In such cases, you might hear the starter motor turning, but the engine won't catch.
   

Common Causes of Glow Plug Failure
Several issues can cause the glow plug system to malfunction in the Bobcat 873. Here are the most common causes:

1. Blown Glow Plugs
   Glow plugs can burn out over time, especially if the engine is subjected to frequent cold starts. A single faulty or blown glow plug can cause hard starting problems.
   • Symptoms: Engine cranks, but doesn’t start, or takes significantly longer to start.
     
   • Solution: Test each glow plug individually to identify which one is faulty, and replace it if necessary.
     
2. Faulty Glow Plug Relay
   The glow plug relay is responsible for controlling the power to the glow plugs. If the relay fails, it can prevent the glow plugs from receiving the necessary current to heat up.
   • Symptoms: The glow plug light doesn’t illuminate on the dashboard, or the engine won’t start even after cranking.
     
   • Solution: Check the glow plug relay with a multimeter to ensure it’s operating properly. Replace it if defective.
     
3. Wiring or Fuse Problems
   The wiring that connects the glow plugs to the relay or the battery can degrade or become corroded, interrupting the current flow to the glow plugs. A blown fuse could also prevent the system from working.
   • Symptoms: Intermittent starting issues or no power to the glow plugs.
     
   • Solution: Inspect the wiring for damage, corrosion, or loose connections. Check the fuse box and replace any blown fuses.
     
4. Faulty Temperature Sensor
   The temperature sensor monitors the engine's coolant or intake temperature and helps regulate the glow plug system’s operation. If the temperature sensor is malfunctioning, it may not signal the glow plugs to activate properly.
   • Symptoms: Glow plugs may stay on longer than necessary or not activate at all.
     
   • Solution: Check the temperature sensor for proper functionality. If it’s faulty, replace it to ensure the glow plug system operates correctly.
     
5. Weak or Discharged Battery
   A weak or discharged battery may not provide sufficient voltage to power the glow plugs. Glow plugs require a certain amount of electrical current to heat up, and if the battery is weak, the glow plugs won’t function as they should.
   • Symptoms: Slow or weak cranking, or no cranking at all.
     
   • Solution: Check the battery charge and ensure it's properly charged. Replace the battery if necessary.
     

Troubleshooting the Glow Plug System in Bobcat 873
Here’s a step-by-step guide to troubleshoot the glow plug system in the Bobcat 873:

1. Step 1: Inspect the Glow Plug Indicator Light
   • Turn the ignition key to the "on" position but do not start the engine.
     
   • Look for the glow plug indicator light on the dashboard. This light should illuminate and stay on for a few seconds before turning off.
     
   • If the light does not come on, there may be an issue with the relay or fuse.
     
2. Step 2: Test the Glow Plugs
   • With a multimeter, check the resistance of each glow plug. A good glow plug should show low resistance, indicating that it can conduct electricity.
     
   • If a glow plug shows high resistance or an open circuit, it is faulty and needs to be replaced.
     
3. Step 3: Check the Glow Plug Relay
   • Locate the glow plug relay and test it with a multimeter. It should provide continuity when it is activated.
     
   • If the relay fails the test, replace it.
     
4. Step 4: Inspect the Wiring and Fuses
   • Check the wiring to ensure there are no breaks, corrosion, or loose connections.
     
   • Inspect the fuses in the fuse box, especially those related to the glow plug system, and replace any blown fuses.
     
5. Step 5: Inspect the Temperature Sensor
   • Test the engine coolant or intake temperature sensor to ensure it is providing the correct readings to the glow plug system.
     
   • If the sensor is faulty, replace it to ensure proper operation of the glow plug system.
     
6. Step 6: Test the Battery Voltage
   • Measure the voltage of the battery. It should read around 12.6 volts when fully charged.
     
   • If the battery voltage is low, recharge or replace the battery as needed.
     

Preventing Glow Plug Issues
While some glow plug issues are inevitable due to wear and tear, there are steps you can take to prevent problems from arising in the future:

• Perform Regular Maintenance: Regular maintenance and timely replacement of worn-out components, such as glow plugs, relays, and fuses, can prevent many issues.
  
• Use Proper Starting Procedures: Always wait for the glow plug indicator light to turn off before attempting to start the engine, especially in cold weather.
  
• Keep the Battery in Good Condition: Ensure the battery is properly maintained, as a weak battery can lead to glow plug problems.
  
• Check for Corrosion: Inspect the wiring and connections regularly for signs of corrosion, and clean them to ensure good electrical conductivity.
  

Conclusion
Glow plug issues are a common cause of starting problems in Bobcat 873 skid steer loaders, especially in colder climates. By understanding the function of glow plugs and their common failure points, operators can quickly diagnose and address any issues. Regular maintenance, thorough troubleshooting, and prompt replacement of faulty components can ensure that the Bobcat 873 remains reliable and performs optimally.