Why Engine RPM Drops in the Basket of a JLG 45IC Boom Lift

[MikePhua]

The JLG 45IC and Its Role in Elevated Work
The JLG 45IC is a mid-sized articulating boom lift designed for indoor and outdoor use, offering a working height of approximately 51 feet and a horizontal outreach of 25 feet. Manufactured by JLG Industries, a company founded in 1969 and now part of Oshkosh Corporation, the 45IC was developed to meet the growing demand for compact, maneuverable lifts with internal combustion power. It became popular in construction, maintenance, and industrial settings where electric models lacked the torque or runtime needed for extended outdoor work.
The 45IC features a gasoline or diesel engine, hydraulic drive, and proportional controls both at the ground and in the platform. Its design emphasizes operator safety, precise movement, and fuel efficiency. However, one recurring issue reported by users is the drop in engine RPM when operating from the basket, especially during boom articulation or drive commands.
Understanding RPM Behavior in Elevated Controls
Engine RPM in boom lifts is managed by a combination of throttle control, hydraulic demand, and electronic logic. When operating from the ground, the engine often runs at full throttle or responds immediately to joystick input. In the basket, however, RPM may be governed differently to reduce noise, conserve fuel, or comply with safety protocols.
Key factors influencing RPM drop include:

• Demand-based throttle control: The system increases RPM only when hydraulic flow exceeds a threshold.
  
• Idle logic: If no movement is detected, the engine returns to low idle to reduce emissions and wear.
  
• Platform priority delay: Some models include a delay or ramp-up curve to prevent sudden movement from the basket.
  
• Faulty foot switch or interlock: If the foot switch in the basket is worn or misaligned, it may not signal full engagement, causing the engine to remain at idle.
  

In one case, a technician in Colorado diagnosed a JLG 45IC with sluggish boom response. The issue was traced to a sticky foot switch that intermittently failed to engage, preventing the engine from ramping up. Replacing the switch restored normal operation.
Key Terminology and System Components
To troubleshoot RPM issues, it helps to understand the following terms:

• Hydraulic demand sensing: A system that adjusts engine speed based on fluid flow requirements.
  
• Foot switch interlock: A safety device that must be depressed to enable platform controls.
  
• Proportional valve: A valve that modulates hydraulic flow based on joystick input.
  
• ECU (Engine Control Unit): The electronic brain that manages throttle, ignition, and sensor feedback.
  
• Load sense line: A hydraulic line that communicates pressure demand to the pump and throttle system.
  

If any of these components fail or become miscalibrated, the engine may not respond appropriately to platform commands.
Diagnostic Steps and Solutions
To resolve RPM drop issues in the basket, follow a structured approach:

• Inspect the foot switch for wear, corrosion, or misalignment
  
• Check platform control wiring for loose connectors or damaged insulation
  
• Verify hydraulic pressure at the control valve during joystick actuation
  
• Test throttle response from both ground and basket controls
  
• Examine ECU fault codes using a diagnostic tool or service interface
  

If the engine responds correctly from the ground but not from the basket, the issue likely lies in the interlock or control signal path. In one documented case, a lift in a warehouse failed to rev up from the basket due to a broken wire in the boom harness. The wire had fatigued from repeated articulation and was repaired with a splice and heat shrink tubing.
Preventive Measures and Operator Tips
To avoid RPM issues and ensure smooth operation:

• Perform weekly inspections of control switches and wiring
  
• Lubricate foot switches and pivot points to prevent sticking
  
• Train operators to fully depress the foot switch before joystick movement
  
• Avoid rapid cycling of controls, which can confuse demand sensing logic
  
• Keep hydraulic fluid clean and within recommended viscosity range
  

Installing a visual indicator for throttle engagement in the basket can help operators confirm that the system is responding. Some fleets retrofit LED indicators or audible buzzers tied to the throttle circuit.
Stories from the Field
A maintenance crew in Florida used a JLG 45IC to service lighting in a stadium. During operation, the engine repeatedly dropped to idle mid-lift. After inspection, they discovered that the platform control box had water intrusion from a recent rainstorm. Drying the box and resealing the grommets resolved the issue.
In another case, a contractor in Oregon replaced the engine on a 45IC but forgot to calibrate the throttle linkage. The lift ran fine from the ground but failed to respond in the basket. A technician adjusted the linkage and updated the ECU parameters, restoring full functionality.
Conclusion
Engine RPM drop in the basket of a JLG 45IC is often a symptom of control logic, interlock failure, or hydraulic miscommunication. With careful inspection and understanding of the system architecture, technicians can resolve these issues and restore responsive, safe operation. The 45IC remains a reliable workhorse, and with proper maintenance, its elevated controls can perform as smoothly as its ground station.