Diagnosing Power Loss, Stalling, and Attachment Failure in the Bobcat E35i

[MikePhua]

Introduction to the Bobcat E35i
The Bobcat E35i is a compact, zero-tail-swing mini excavator designed for versatility in tight workspaces. Part of the E-Series lineup, this 3.5-ton machine gained popularity for its fuel efficiency, advanced hydraulics, and electronically controlled engine. The “i” in the model name denotes Bobcat’s intelligent engine control system, which dynamically adjusts RPM and hydraulic flow for better fuel economy and smoother operation. Despite its advantages, the E35i is not immune to performance issues—especially those involving power loss, engine stalling, and malfunctioning hydraulic attachments like the X-Change quick coupler system.
Common Symptoms and Operator Observations
In several field reports involving the 2014 Bobcat E35i, operators described similar, frustrating symptoms:

• The machine starts but stalls quickly when any hydraulic control is engaged.
  
• There’s a noticeable loss of power under load, especially when swinging or lifting.
  
• The X-Change hydraulic quick coupler system does not operate at all.
  
• Fuel usage appears higher than expected, despite limited working time.
  
• The engine surges at idle or hesitates under acceleration.
  

These symptoms are often interconnected and point to a systemic issue involving fuel delivery, hydraulics, and possibly electrical control.
Understanding the E35i’s Engine and Hydraulic Architecture
The 2014 E35i is powered by a Tier 4-compliant, electronically controlled Kubota diesel engine. Instead of using a Diesel Particulate Filter (DPF), the engine relies on a common rail fuel system and Exhaust Gas Recirculation (EGR) to meet emissions standards. It integrates with Bobcat’s control module to manage engine RPM, hydraulic priorities, and auto-idle features.
Key components influencing machine performance include:

• Fuel injection pump (common rail): Precisely meters fuel delivery under high pressure.
  
• Fuel filters: Protect injectors from contaminants and water.
  
• Hydraulic load-sensing pump: Adjusts flow based on operator inputs.
  
• Pilot control valves: Convert joystick movements into pilot pressure.
  
• Control module (ECU): Manages engine speed, hydraulic flow, and safety interlocks.
  
• X-Change coupler solenoid: Electrically actuated valve controlling attachment release.
  

Failures in any of these areas can cascade into broader issues that degrade machine performance.
Investigating the Root Causes
When a machine stalls under load and shows no power in the hydraulic coupler, the following causes should be considered in order of likelihood:

• Fuel starvation: Clogged primary or secondary fuel filters can restrict flow, especially under high-load conditions. Water in fuel or degraded fuel quality may also be culprits.
  
• Suction-side air leaks: Cracked or loose fuel lines on the suction side of the pump allow air ingress, which disrupts combustion and causes stalling.
  
• Lift pump malfunction: An electric or mechanical lift pump that fails intermittently can starve the injection system when load increases.
  
• Hydraulic overpressure: A jammed or improperly adjusted relief valve may cause system drag, overloading the engine and triggering a stall.
  
• Stuck diverter valve: If the diverter valve feeding the X-Change system is stuck or the solenoid is burnt out, it can interrupt hydraulic priority logic, affecting other circuits.
  
• Electronic control fault: A bad ground, corroded connector, or software glitch in the ECU may prevent the proper allocation of fuel and hydraulic control, especially during simultaneous input.
  

Case Story: The Hidden Air Leak
In one repair scenario, a technician spent several hours chasing what appeared to be an injector or ECU issue, only to discover a tiny pinhole leak in the rubber fuel hose between the tank and the filter head. Under normal operation, the leak didn’t drip fuel, but it allowed air to be sucked in when the pump demanded flow. The result was inconsistent engine stalling and power loss—especially under hydraulic load. Replacing the hose solved the issue instantly.
Electrical Gremlins and the X-Change System
The X-Change coupler system allows operators to swap buckets and attachments from inside the cab using hydraulic actuators. It relies on:

• An electric solenoid valve
  
• A rocker switch or touchpad input
  
• Feedback signals to the controller
  
• Lock pins driven by hydraulic cylinders
  

When the system fails completely (no sound, no movement), likely causes include:

• Blown fuse or relay
  
• Failed solenoid coil
  
• Wiring harness damage
  
• Contaminated fluid causing valve stickiness
  

One operator reported a “dead” coupler system after a washdown with high-pressure water. It turned out the water had forced its way into the coupler solenoid connector, shorting it internally. A new connector and dielectric grease prevented recurrence.
Hydraulic Load and Engine Stalling
In modern mini excavators, engine stalling under load is often due to hydraulic over-demand. Bobcat machines use a hydraulic load-sensing system that adjusts flow and pressure based on pilot input. When the control valve becomes sticky or miscalibrated, it may:

• Demand full pressure from the pump, even under minor control input
  
• Create an artificial “deadhead” condition
  
• Overwhelm the engine’s torque capacity
  

This issue is particularly common after contamination events (dirty hydraulic oil, failed seals) or improper fluid changes.
Preventive Maintenance Tips
To avoid recurring issues with stalling, power loss, and system failure, owners and operators should implement the following practices:

• Replace both fuel filters every 250 hours
  
• Bleed air from the fuel system after any filter change
  
• Inspect suction-side hoses for soft spots, cracks, or loose clamps
  
• Keep all electrical connectors sealed and dry
  
• Use OEM hydraulic fluid and adhere to service intervals
  
• Operate the X-Change system weekly to prevent valve seizing
  

Routine diagnostics with a service laptop or Bobcat handheld tool can also detect hidden ECU or sensor errors before they manifest into hard failures.
Lessons from the Field
The story of a landscape contractor illustrates how minor oversights can snowball. After ignoring a check engine light and limping along for weeks, the E35i finally stalled mid-job and wouldn’t restart. Diagnosis revealed a completely plugged fuel filter caused by algae growth in stored diesel. The mechanic noted the fuel had a "slimy green sheen." The contractor installed a tank filter, began adding biocide to fuel deliveries, and hasn’t had a stall since.
Conclusion
Power loss, stalling, and X-Change system failure in a Bobcat E35i can stem from various mechanical, hydraulic, and electrical issues. Understanding the interplay between these systems is essential to diagnosing and correcting the root cause. While modern diagnostics offer deep insight, basic principles—like clean fuel, airtight suction, and proper electrical grounding—remain as critical today as ever. For owners of Tier 4 mini excavators, preventive maintenance isn’t just a checklist—it’s a necessity for uptime and longevity.