Why Won’t the John Deere 744H Start After Cranking

[MikePhua]

Background on the John Deere 744H
The John Deere 744H is a heavy-duty wheel loader designed for demanding earthmoving and material handling operations. Introduced in the early 2000s as part of Deere’s H-Series, the 744H was built to bridge the gap between mid-size and large loaders. With an operating weight of approximately 25 tons and a net engine power of around 275 hp, it features a robust frame, Z-bar linkage, and a high-capacity bucket system. Its popularity surged in North America, with thousands of units sold to construction firms, mining operations, and municipal fleets.
John Deere, founded in 1837, has maintained a reputation for durable, operator-friendly equipment. The company’s wheel loader segment has consistently ranked among the top three in global sales, with the 744H contributing significantly to its market share during its production run.
Crank No Start Symptoms Explained
When a machine like the 744H cranks but fails to start, it indicates that the starter motor is functioning, but the engine is not receiving the necessary inputs to ignite. This condition typically points to issues in one or more of the following systems:

• Fuel Delivery System: Includes fuel pump, injectors, and filters. If fuel is not reaching the combustion chamber, ignition cannot occur.
  
• Ignition System: In diesel engines, this involves compression and timing rather than spark plugs.
  
• Electronic Control System: The Engine Control Module (ECM) must receive accurate signals from sensors and provide correct outputs.
  
• Sensor Inputs: Crankshaft and camshaft position sensors are critical for timing and fuel injection coordination.
  

Terminology Clarified

• ECM (Engine Control Module): The computer that manages engine functions based on sensor inputs.
  
• Crankshaft Position Sensor: Detects the position and speed of the crankshaft to help the ECM determine timing.
  
• Camshaft Position Sensor: Works in tandem with the crank sensor to ensure proper valve timing and fuel delivery.
  
• Start Inhibit Circuit: A safety feature that prevents engine start under unsafe conditions, often linked to transmission or gear position.
  

Likely Causes of the Issue
In the case of the 744H, the machine was reportedly running fine before being washed. After the wash, it cranked but failed to start, with no RPM signal on the dashboard. This sequence suggests a disruption in the electronic control system, likely due to moisture intrusion or electrical disconnection. Key possibilities include:

• Water Intrusion into Connectors: High-pressure washing can force water into sealed connectors, disrupting signal transmission.
  
• Sensor Signal Loss: If the crank or cam sensor wires are compromised, the ECM cannot synchronize ignition timing.
  
• ECM Power Supply Issues: Voltage readings below specification during cranking may indicate poor grounding or damaged power lines.
  
• Gear Position Miscommunication: If the transmission control unit (TCU) fails to confirm neutral gear, the start inhibit circuit may block ignition.
  

Diagnostic Recommendations
To resolve the issue, technicians should follow a structured diagnostic path:

• Step 1: Verify Gear Position
  Ensure the transmission is in neutral and that the dashboard confirms this. A mismatch may trigger the start inhibit logic.
  
• Step 2: Inspect ECM Voltage
  Measure voltage at ECM power and ground pins during cranking. Values below 20V may indicate resistance or corrosion in the wiring.
  
• Step 3: Check Sensor Resistance
  Use an ohmmeter to measure resistance across crank and cam sensor wires at the ECM connector. Typical values range from 2.5k to 3.5k ohms.
  
• Step 4: Examine Connectors and Harnesses
  Disconnect and inspect all engine-related connectors. Look for moisture, corrosion, or bent pins. Clean with compressed air and apply dielectric grease.
  
• Step 5: Test ECM Functionality
  If all inputs are verified and the ECM still fails to respond, consider swapping with a known-good unit or sending it for bench testing.
  

Real-World Example
In 2022, a Pennsylvania-based field technician encountered a similar issue after washing a 744H. Despite proper cranking, the machine showed no RPM signal and refused to start. After tracing the sensor wires and confirming resistance, the technician discovered that water had entered the ECM connector. Drying the connector and resealing it resolved the issue. This incident led the company to revise its washing procedures, avoiding direct spray on sensitive electrical zones.
Preventive Measures
To avoid future crank-no-start scenarios, operators and maintenance teams should implement the following:

• Avoid Direct Water Spray on ECMs, sensors, and connectors during cleaning.
  
• Use Protective Sleeves on exposed wiring harnesses to prevent abrasion and moisture ingress.
  
• Conduct Regular Electrical Inspections every 500 operating hours.
  
• Apply Dielectric Grease to all critical connectors during service intervals.
  

Conclusion
The crank-no-start condition in the John Deere 744H is often rooted in electrical disruptions, especially following cleaning or maintenance. By understanding the interplay between sensors, ECM, and transmission controls, technicians can efficiently diagnose and resolve the issue. Given the machine’s importance in high-volume operations, ensuring reliable starts is not just a matter of convenience—it’s essential for productivity and safety. With proper diagnostics and preventive care, the 744H can continue to deliver the performance that has made it a staple in the heavy equipment world.