Hard Starting Issue with 4BT Cummins in Lull 644B: Diagnosing Injection Pump Problems

[MikePhua]

Introduction
A common issue faced by many heavy equipment operators and owners is hard starting, especially in machines with diesel engines like the 4BT Cummins engine in the Lull 644B. In this forum discussion, users shared their experiences and troubleshooting methods related to a hard starting problem with the 4BT Cummins engine. The discussion focused on the potential causes of the issue, specifically the injection pump, and offered advice on diagnosing and resolving the problem.
Symptoms of the Hard Starting Issue
The forum members initially discussed the symptoms of the hard starting problem, which were generally characterized by the engine being difficult to start, especially in colder weather. Some of the common symptoms identified were:

• Slow Cranking: The engine cranks slowly but doesn’t fire up immediately. This can be a sign of fuel delivery issues or compression problems.
  
• Difficulty Starting in Cold Weather: The engine starts harder in cold temperatures, which often points to fuel or glow plug issues.
  
• Unstable Idle After Starting: After the engine starts, the idle is rough or inconsistent, suggesting that the fuel system or injection timing may be off.
  

Potential Causes of Hard Starting
Several potential causes for hard starting were discussed, with many forum members agreeing that the issue could be related to the fuel system, particularly the injection pump.

• Fuel Delivery Problems: A common cause for hard starting is inadequate fuel delivery. Several members mentioned the possibility of clogged fuel filters, air in the fuel lines, or a failing lift pump, which could result in insufficient fuel being supplied to the engine for proper combustion.
  • Air in the Fuel Lines: Air trapped in the fuel lines can lead to hard starting because the injection pump will not receive a steady supply of fuel.
    
• Injection Pump Issues: The injection pump plays a critical role in supplying fuel to the engine at the correct timing and pressure. A malfunctioning pump could cause the fuel to be injected at the wrong time, which can lead to poor combustion, rough idling, and difficulty starting the engine.
  • Symptoms of a Failing Injection Pump: Members noted that a failing injection pump can result in uneven fuel distribution or improper fuel pressure, leading to hard starting. This is often accompanied by rough idle and performance loss.
    
  • Injector Timing: Incorrect injector timing caused by a failing injection pump can result in fuel being injected too early or too late, affecting combustion efficiency and causing starting issues.
    
• Glow Plugs and Cold Weather: Some members suggested checking the glow plugs, especially since hard starting is more common in colder weather. If the glow plugs are malfunctioning, the engine may not reach the necessary temperature for proper combustion during cold starts.
  • Glow Plug Functionality: Inadequate heating from glow plugs can lead to incomplete combustion, making it difficult for the engine to start.
    
• Compression Issues: Another possible cause of hard starting could be low compression in the cylinders. This may be the result of worn engine components, such as piston rings or valve seals, and could lead to insufficient compression for ignition.
  

Diagnosing the Problem
Several members offered advice on how to diagnose the hard starting issue, with a focus on systematically checking different components of the engine and fuel system.

• Check Fuel Filters: The first step in diagnosis is often checking the fuel filters. A clogged filter can restrict fuel flow, leading to hard starting. Members recommended replacing the fuel filter and ensuring that there are no obstructions in the fuel lines.
  • Check for Fuel Contamination: Inspecting the fuel for any signs of contamination or water was also suggested. Contaminated fuel can cause poor combustion and starting issues.
    
• Inspect the Injection Pump: If fuel filters are clear, the next logical step is to check the injection pump. It is recommended to check the pump’s performance using diagnostic tools to measure fuel pressure and timing. Any discrepancies could indicate a failing pump.
  • Testing the Pump: Some forum members suggested that the pump should be tested under load to ensure that it is delivering the correct amount of fuel at the right time. In some cases, if the pump is determined to be defective, it might need to be replaced or rebuilt.
    
• Check for Air Leaks: Another key aspect is checking for air leaks in the fuel lines. A simple leak in the lines can allow air to enter, disrupting the fuel supply and causing starting problems. Members recommended inspecting the lines for any visible cracks or signs of wear and replacing any faulty seals or hoses.
  
• Glow Plug Inspection: In colder weather, checking the glow plugs is essential. If they are not functioning correctly, the engine may struggle to start in low temperatures. Members advised testing each glow plug individually and replacing any that are faulty.
  
• Compression Test: If the fuel system and glow plugs seem to be functioning correctly, a compression test is the next step. A drop in compression can result in hard starting, especially in older engines. A compression test will reveal if the engine’s internal components need attention, such as replacing piston rings or valve seals.
  

Solutions and Fixes
Once the source of the issue has been diagnosed, forum members shared several potential solutions and fixes for the hard starting problem.

• Replace the Injection Pump: If the injection pump is determined to be faulty, members suggested either rebuilding or replacing it with a new or remanufactured unit. Ensuring the correct installation and timing is critical to avoid future issues.
  
• Replace Faulty Glow Plugs: Replacing the glow plugs is often an easy fix for starting issues, especially in cold weather. Members recommended checking the glow plug circuit and ensuring the relay and wiring are also in good condition.
  
• Fuel System Repairs: If air is detected in the fuel lines, repairing or replacing the damaged hoses or seals can eliminate the issue. In some cases, installing a new lift pump may be necessary to ensure proper fuel flow.
  
• Engine Overhaul for Compression Issues: If low compression is identified, a more extensive repair, such as an engine overhaul, may be required. This can involve replacing piston rings, valve seals, and other internal components to restore engine performance.
  

Conclusion
Hard starting in the 4BT Cummins engine in the Lull 644B is a common issue that can be caused by a variety of factors, including fuel delivery problems, a failing injection pump, malfunctioning glow plugs, and low compression. Diagnosing the problem systematically by inspecting the fuel system, injection pump, glow plugs, and compression can help pinpoint the cause. Once identified, the appropriate solutions, such as replacing faulty components or performing repairs, can restore reliable starting and ensure optimal engine performance.