Diagnosing Fuel Delivery Issues in Compact Loaders

[MikePhua]

The Bobcat MT50 and Its Role in Compact Equipment
The Bobcat MT50 mini track loader was introduced as part of Bobcat’s early push into ultra-compact equipment for landscaping, utility work, and tight-access construction. Bobcat, founded in 1947 in North Dakota, became synonymous with skid steers and compact loaders. The MT50, weighing around 2,500 pounds and powered by a small diesel engine, was designed for maneuverability and light-duty tasks in confined spaces.
Though no longer in production, the MT50 remains popular among rental fleets and small contractors. Its mechanical simplicity makes it easy to maintain, but age-related issues—especially in the fuel system—can cause frustrating performance problems.
Symptoms of Fuel System Failure
A common issue in older MT50 units is poor idling or refusal to start. The engine may crank but barely run, often mimicking symptoms of water-contaminated fuel. Operators report:

• Weak or erratic idle
  
• Delayed throttle response
  
• Fuel starvation under load
  
• Difficulty bleeding air from the system
  

Terminology:

• Lift Pump: A low-pressure pump that draws fuel from the tank and delivers it to the injection system.
  
• Injector Block: The manifold where fuel is distributed to individual injectors.
  
• Fuel Conditioner: An additive used to prevent gelling, water contamination, and microbial growth.
  

In one case, the fuel line routing was questioned. The operator assumed fuel should flow from the tank to the filter, then to the pump and injectors. However, the correct configuration for many compact diesels is tank → lift pump → filter → injector block. This ensures the pump receives unfiltered fuel and pushes it through the filter under pressure.
Clogged Screens and Internal Pump Contamination
Upon disassembly of the lift pump, two internal screens were discovered—one at the inlet and another at the outlet. The inlet screen was completely clogged with debris, restricting flow and starving the engine. Cleaning these screens restored normal operation.
This highlights a critical point: many compact machines lack external pre-filters, relying instead on internal screens that are often overlooked. These screens can trap:

• Rust flakes from aging tanks
  
• Fuel algae from biofuel contamination
  
• Rubber fragments from deteriorating hoses
  

Suggested upgrades:

• Install a diesel-rated inline filter before the lift pump
  
• Use clear fuel lines to visually inspect flow
  
• Replace old rubber hoses with biofuel-compatible variants
  

Biofuel and Fuel Algae Complications
The introduction of biodiesel blends has brought unintended consequences. Older machines with rubber fuel lines are especially vulnerable. Biofuel can cause:

• Swelling and softening of rubber hoses
  
• Delamination of inner hose linings
  
• Accelerated microbial growth (fuel algae)
  

Fuel algae, despite the name, is actually a bacterial and fungal colony that thrives in water-contaminated diesel. It forms slimy mats that clog screens, filters, and suction ports. One operator reported cleaning at least one tank per month due to algae buildup, especially in machines stored outdoors or used infrequently.
Preventive measures:

• Use biocide additives in diesel fuel
  
• Drain water from tanks regularly
  
• Store machines with full tanks to reduce condensation
  

Testing Fuel Pressure and Flow
To confirm fuel delivery issues, a simple pressure test can be performed:

• Install a T-fitting in the fuel line before the injector pump
  
• Connect a low-pressure gauge (0–15 psi range)
  
• Crank the engine and observe pressure
  

A healthy lift pump should produce 3–7 psi. If pressure is absent or erratic, the pump may be failing or obstructed. Loosening the hose at the injector pump inlet should result in fuel leakage—if not, flow is insufficient.
Recommended diagnostic tools:

• Vacuum/pressure gauge from an auto parts store
  
• Clear fuel line segments for visual inspection
  
• Hand primer bulb for manual bleeding
  

Field Story from Pennsylvania
A mechanic in Elizabethtown, PA acquired a used Bobcat MT50 that barely idled. After draining the tank, replacing the filter, and confirming fuel conditioner was present, the issue persisted. He traced the problem to the lift pump, which produced almost no flow. Upon disassembly, he found the inlet screen packed with debris. After cleaning and reassembling, the machine ran smoothly.
He later added a diesel-rated inline filter before the pump and replaced all hoses with ethanol-resistant tubing. The machine has since operated without issue, even in winter conditions.
Conclusion
Fuel problems in compact loaders like the Bobcat MT50 often stem from overlooked components—internal screens, degraded hoses, and microbial contamination. Understanding the correct fuel flow path and performing simple pressure tests can save hours of guesswork. With proper filtration, hose upgrades, and seasonal additives, these machines can continue to perform reliably despite their age. For operators and mechanics alike, the key is vigilance and a willingness to look beyond the obvious.