Air Intrusion in the Fuel System of the Terex TA27 with Cummins Engine

[MikePhua]

The Terex TA27 and Its Powertrain Configuration
The Terex TA27 articulated dump truck was designed for mid-range hauling in construction, mining, and quarry operations. Manufactured by Terex Corporation, a company with roots dating back to 1933, the TA27 was part of a successful line of articulated haulers that gained traction in North America and Europe during the early 2000s. The TA27 typically features a Cummins QSB6.7 or QSM11 diesel engine, known for its torque-rich performance and electronic fuel control.
Cummins, founded in 1919, has supplied millions of engines globally, with the QSB and QSM series powering everything from excavators to marine vessels. These engines rely on high-pressure fuel systems and precise metering to maintain combustion efficiency. However, even minor air intrusion can disrupt performance, leading to hard starts, stalling, and erratic throttle response.
Symptoms of Air in the Fuel Filter
Operators of the TA27 have reported persistent air bubbles in the fuel filter housing, especially after shutdown or during cold starts. Common symptoms include:

• Engine cranks but fails to start
  
• Loss of power under load
  
• Fuel filter housing not remaining full
  
• Visible air bubbles in the clear filter bowl
  
• Frequent priming required to restore operation
  

These issues often point to air entering the system upstream of the fuel filter, either through cracked lines, loose fittings, or faulty seals.
Typical Causes of Air Intrusion
Air can enter the fuel system through several pathways:

• Cracked fuel lines, especially rubber sections near the tank or engine
  
• Loose hose clamps or fittings at the lift pump or filter head
  
• Faulty fuel filter gaskets or improperly seated filters
  
• Leaking primer pumps or manual bleed screws
  
• Tank pickup tubes with pinholes or poor sealing
  

In one documented case, a technician traced the issue to a cracked plastic fuel line near the tank bulkhead. The line allowed air to enter when the engine was off, causing the filter to drain overnight. Replacing the line with reinforced rubber tubing resolved the issue permanently.
Fuel System Architecture and Pressure Zones
The TA27’s fuel system includes:

• Fuel tank with pickup tube and return line
  
• Lift pump (mechanical or electric) to draw fuel to the filter
  
• Primary and secondary fuel filters
  
• High-pressure injection pump
  
• Return line to tank
  

Air intrusion typically occurs in the suction side—between the tank and lift pump—where vacuum pressure can draw air through even microscopic leaks. Once air enters, it accumulates in the filter housing and disrupts flow to the injection pump.
Diagnostic Techniques and Field Solutions
To locate the source of air:

• Install a clear hose between the tank and lift pump to observe bubbles
  
• Use a vacuum gauge to test for pressure drop along the line
  
• Pressurize the tank slightly and inspect for leaks using soap solution
  
• Replace suspect lines with transparent tubing for visual confirmation
  
• Bypass the lift pump temporarily to isolate the fault
  

A contractor in Alberta shared that after replacing all rubber lines with braided fuel hose and sealing each fitting with thread compound, his TA27 ran flawlessly for over 1,000 hours without priming.
Terminology Notes

• Lift Pump: A low-pressure pump that draws fuel from the tank to the filter system
  
• Fuel Filter Head: The mounting base for the fuel filter, often containing valves and sensors
  
• Primer Pump: A manual or electric pump used to purge air from the fuel system
  
• Suction Side: The portion of the fuel system under vacuum, before the lift pump
  
• Return Line: The hose that carries unused fuel back to the tank
  

Preventive Measures and Recommendations
To prevent future air intrusion:

• Replace fuel lines every 3 years or 2,000 hours
  
• Use fuel-rated clamps and avoid worm-drive types
  
• Inspect filter seals during every service interval
  
• Keep the tank above half full to reduce vacuum stress
  
• Install a check valve near the tank to prevent backflow
  

For machines operating in cold climates, consider using fuel heaters and winter-grade diesel to reduce viscosity and improve flow. Always prime the system after filter changes and monitor the filter bowl for air accumulation.
Conclusion
Air in the fuel system of the Terex TA27 with a Cummins engine is a deceptively simple problem that can lead to major operational headaches. By understanding the system layout, identifying weak points, and applying targeted diagnostics, operators can restore reliability and avoid costly downtime. With proper maintenance and attention to detail, the TA27 remains a dependable workhorse across demanding haul routes and rugged terrain.