08-20-2025, 06:25 PM
Machine Overview
The Lull 844B Highlander is a rugged telehandler famous for its high lift capacity and reach, making it a staple in heavy duty construction, industrial, and material handling applications. It features an 8,000 lb lift capacity and a maximum lift height of approximately 42 feet, supported by a robust John Deere 3.9L inline 4-cylinder turbocharged diesel engine delivering about 110 horsepower. Weighing roughly 23,160 lbs, the 844B Highlander combines power with maneuverability thanks to its four-wheel steering and outboard planetary drive axles. Its hydraulic system controls boom extension, fork tilt, and carriage positioning with precision, ensuring reliable handling of heavy and bulky loads.
Issue Description
A recurring performance concern with this telehandler model is an unusual driving behavior characterized by the machine slowing down to a complete stop uncontrollably, then suddenly accelerating back up, which can be unsettling and potentially hazardous on job sites. This issue might manifest intermittently and without obvious warning lights or fault codes.
Potential Causes
In one case, a construction site operating a Lull 844B Highlander experienced periodic machine slow-downs followed by unexpected speed surges while carrying heavy loads. Service technicians traced the root cause to a faulty throttle position sensor intermittently sending erratic signals to the ECM. Upon sensor replacement and recalibration, the telehandler resumed smooth operation, enhancing site safety and operator confidence.
Conclusion
The Lull 844B Highlander’s power and reach make it a valuable asset, but unusual slow-down and surge behaviors should prompt prompt inspection of the hydraulic transmission, electronic controls, sensors, and hydraulic fluid systems. Systematic diagnostic approaches focusing on sensors and hydraulic integrity will often resolve these performance irregularities, ensuring the telehandler operates safely and efficiently under demanding conditions.
The Lull 844B Highlander is a rugged telehandler famous for its high lift capacity and reach, making it a staple in heavy duty construction, industrial, and material handling applications. It features an 8,000 lb lift capacity and a maximum lift height of approximately 42 feet, supported by a robust John Deere 3.9L inline 4-cylinder turbocharged diesel engine delivering about 110 horsepower. Weighing roughly 23,160 lbs, the 844B Highlander combines power with maneuverability thanks to its four-wheel steering and outboard planetary drive axles. Its hydraulic system controls boom extension, fork tilt, and carriage positioning with precision, ensuring reliable handling of heavy and bulky loads.
Issue Description
A recurring performance concern with this telehandler model is an unusual driving behavior characterized by the machine slowing down to a complete stop uncontrollably, then suddenly accelerating back up, which can be unsettling and potentially hazardous on job sites. This issue might manifest intermittently and without obvious warning lights or fault codes.
Potential Causes
- Hydraulic Transmission Malfunction: The 844B uses a hydraulically controlled powershift transmission; internal valve blockages or pump irregularities can cause intermittent power loss and surges.
- Electronic Control System Errors: The telehandler’s electronic control module (ECM) managing engine and transmission functions may intermittently misread sensor inputs or have software glitches inducing unintended throttle or drive commands.
- Engine Load Sensing Issues: Faulty sensors detecting hydraulic load or engine RPM can send misleading data, causing the system to adjust power improperly, resulting in slowing down and sudden acceleration.
- Throttle Linkage or Sensor Faults: Physical faults with throttle controls or malfunctioning sensors can translate to erratic engine speed attempts.
- Hydraulic Oil Condition and Pressure Fluctuations: Hydraulic fluid contamination or abnormal pressure variations may disrupt smooth power application to wheels or tracks.
- Perform a thorough inspection of hydraulic filters, pumps, and control valves for wear, damage, or clogging.
- Scan the ECM for stored diagnostic trouble codes which may guide toward faulty sensors or software malfunctions.
- Verify the proper functioning of throttle position sensors and engine load sensors, replacing those that fail calibration tests.
- Test the hydraulics for consistent pressure outputs under varying load conditions; replace contaminated oil and filters as necessary.
- Consider software updates or controller resets recommended by the manufacturer to address ECM logic errors.
- Observe machine operation and record conditions under which the slow-down/surge events occur, aiding targeted troubleshooting.
- Powershift Transmission: A transmission type that shifts gears hydraulically under load without interrupting power.
- Electronic Control Module (ECM): Onboard computer controlling engine and transmission functions based on sensor inputs.
- Throttle Position Sensor: Measures the position of the throttle to regulate engine speed.
- Hydraulic Pump: Device that converts mechanical power to fluid power, driving hydraulic motors and actuators.
- Load Sensing: Technology used in hydraulics to adapt flow and pressure based on the workload.
In one case, a construction site operating a Lull 844B Highlander experienced periodic machine slow-downs followed by unexpected speed surges while carrying heavy loads. Service technicians traced the root cause to a faulty throttle position sensor intermittently sending erratic signals to the ECM. Upon sensor replacement and recalibration, the telehandler resumed smooth operation, enhancing site safety and operator confidence.
Conclusion
The Lull 844B Highlander’s power and reach make it a valuable asset, but unusual slow-down and surge behaviors should prompt prompt inspection of the hydraulic transmission, electronic controls, sensors, and hydraulic fluid systems. Systematic diagnostic approaches focusing on sensors and hydraulic integrity will often resolve these performance irregularities, ensuring the telehandler operates safely and efficiently under demanding conditions.
