Electrical System Diagnosis and Starting Challenges on the Lull 644 Telehandler

[MikePhua]

Lull’s Telehandler Legacy and the 644 Series
Lull telehandlers, originally developed by Lull Engineering Company in Minnesota, became known for their unique sliding boom design, which allowed operators to precisely place loads without repositioning the machine. The Lull 644 series, including variants like the 644B, 644C, and 644E, was widely adopted in the 1980s and 1990s for framing, masonry, and general construction. With a lift capacity of 6,000 pounds and a reach of over 40 feet, the 644 became a staple on job sites across North America.
After several corporate transitions, including acquisition by JLG Industries, Lull-branded machines were eventually phased out, but thousands remain in service. Most 644 units are powered by John Deere diesel engines, typically the 4239 or 4045T series, known for their reliability but also for their cold-start quirks.
Terminology Annotation

• Group 31 Battery: A heavy-duty commercial battery commonly used in diesel equipment, offering high cranking amps and deep-cycle durability.
  
• 2/0 Cable: A thick gauge battery cable used to minimize voltage drop over long runs, essential for high-current applications like starting diesel engines.
  
• De-stroke Solenoid: A valve that temporarily unloads hydraulic pump pressure during engine start-up, reducing starter load.
  

Is the Lull 644 a 12V or 24V System
Despite speculation, the Lull 644 series is factory-configured as a 12-volt system. This applies across all major variants, including the Highlander and later models. While some machines may appear to support dual batteries, they are wired in parallel to maintain 12V output, not in series for 24V.
Operators encountering slow cranking often suspect a voltage mismatch, but the issue typically lies elsewhere. Confirming system voltage can be done by inspecting:

• Alternator stampings near the mounting flange
  
• Starter motor tags
  
• Hydraulic solenoid coil labels
  
• Dashboard gauge voltage ranges
  

These components are often difficult to access, but they provide definitive answers when visible.
Slow Cranking Causes and Solutions
A common complaint with the Lull 644 is sluggish cranking, especially in cold weather. Several factors contribute to this:

• Long cable runs from battery to starter, increasing resistance
  
• Undersized battery cables, especially if replaced with automotive-grade wire
  
• Weak or aging starter motor
  
• Cold hydraulic systems applying load during startup
  
• Poor grounding or corroded terminals
  

In one documented case, a Genie telehandler with a similar John Deere 4045T engine suffered from slow cranking due to a single battery mounted far from the engine. After relocating the battery box and adding a second Group 31 battery with short 2/0 cables, the machine started reliably even in winter.
Recommendations for Reliable Starting
To improve cold-start performance and reduce strain on electrical components:

• Use two Group 31 batteries wired in parallel
  
• Install 2/0 gauge cables with minimal length between battery and starter
  
• Clean all terminals and inspect for internal cable corrosion
  
• Replace the starter if it sounds rough or labors during cranking
  
• Add a block heater to pre-warm the engine in cold climates
  
• Check for hydraulic pump load during startup and consider installing a de-stroke solenoid if applicable
  

Fuel Delivery and Injection Pump Troubleshooting
After resolving electrical issues, some operators find that the engine still fails to start due to lack of fuel at the injectors. This can be caused by:

• Faulty lift pump not supplying fuel to the injection pump
  
• Failed shutoff solenoid preventing fuel delivery
  
• Air leaks in rubber grommets or cracked filter housings
  
• Stubborn injection pump requiring priming
  

To diagnose:

• Verify 12V power at the shutoff solenoid and listen for a click
  
• Loosen injector lines and crank the engine to check for fuel spray
  
• Use a temporary 12V electric fuel pump to push fuel through the system
  
• Mist a small amount of gasoline into the intake while cranking to encourage combustion and purge air
  

One technician revived a Deere-powered telehandler by misting fuel into the intake while holding the throttle wide open. After a few seconds of assisted combustion, the injection pump began delivering fuel, and the engine ran normally.
Starter and Injection Pump Replacement Tips
When sourcing replacement parts:

• Identify the starter by its mounting pattern (e.g., two-hole flange)
  
• Match injection pump model and serial number before ordering
  
• Consider replacing only the shutoff solenoid if the pump body is intact
  
• Use OEM or high-quality aftermarket parts to ensure compatibility
  

Conclusion
The Lull 644 telehandler operates on a 12-volt electrical system, and slow cranking is typically caused by cable resistance, starter wear, or hydraulic load—not voltage mismatch. By upgrading cables, adding batteries, and inspecting fuel delivery components, operators can restore reliable starting and extend the life of these rugged machines. With thousands still in use, the 644 remains a testament to durable design and field-serviceable engineering.