Diagnosing Injector Pulse Failure After Engine Overhaul on a JCB JS160

[MikePhua]

The JS160 and JCB’s Excavator Engineering
The JCB JS160 is a mid-size hydraulic excavator designed for general construction, earthmoving, and utility work. With an operating weight around 17 metric tons and a dig depth exceeding 6 meters, the JS160 is powered by a turbocharged diesel engine—typically a JCB Dieselmax or Isuzu-sourced unit depending on market and year. These engines are electronically controlled and rely on precise timing signals from sensors to manage fuel injection and combustion.
JCB, founded in 1945 in Staffordshire, England, has grown into one of the world’s leading manufacturers of construction equipment. The JS series excavators are known for their robust undercarriage, smooth hydraulic response, and increasingly sophisticated electronic control systems introduced in the 2000s.
Engine Overhaul and Post-Rebuild Challenges
After a full engine overhaul, the JS160 in question failed to start. The crankshaft sensor was replaced, but no injector pulse was detected across all four injectors. This points to a failure in the electronic fuel injection system, which depends on synchronized signals from the engine control unit (ECU) and sensor inputs to trigger injector actuation.
Common post-overhaul issues include:

• Incorrect crankshaft sensor installation or incompatible part
  
• Damaged wiring harness during engine reinstallation
  
• ECU not receiving or interpreting timing signals
  
• Immobilizer or security system interference
  
• Faulty camshaft position sensor (if equipped)
  

The absence of injector pulse suggests that the ECU is not initiating fuel delivery, likely due to missing or invalid timing data.
Crankshaft Sensor Function and Signal Dependency
The crankshaft position sensor (CKP) is a critical component in electronically controlled diesel engines. It detects the rotational position and speed of the crankshaft using a toothed reluctor wheel and sends this data to the ECU. The ECU uses this information to determine injection timing and engine synchronization.
If the CKP sensor is:

• Misaligned
  
• Incorrectly gapped
  
• Damaged internally
  
• Incompatible with the ECU firmware
  

Then the ECU may fail to generate injector pulses. Some systems also require a valid camshaft position signal to confirm cylinder identification, especially during startup.
Diagnostic steps:

• Verify CKP sensor part number and compatibility
  
• Check sensor gap using feeler gauge (typically 0.5–1.0 mm)
  
• Inspect wiring continuity from sensor to ECU
  
• Use oscilloscope to confirm signal waveform during cranking
  
• Scan ECU for fault codes using diagnostic software
  

Injector Pulse Absence and ECU Lockout Conditions
Modern ECUs include safety protocols that prevent injector actuation under certain conditions. These include:

• No crankshaft signal
  
• Engine immobilizer active
  
• Low battery voltage
  
• Faulty engine speed sensor
  
• Incorrect ECU programming
  

If the ECU does not detect a valid crank signal, it will not energize the injectors. In some cases, the ECU may require a reset or reprogramming after sensor replacement. Battery voltage during cranking should exceed 10.5V to ensure stable ECU operation.
Solutions:

• Perform ECU reset using diagnostic tool
  
• Confirm immobilizer status and key recognition
  
• Check battery health and starter draw
  
• Reflash ECU firmware if corrupted
  

A Story from the Field
In Harare, a technician completed an overhaul on a JS160 and replaced the crankshaft sensor. Despite proper installation, the engine refused to start. After hours of tracing wiring and testing injectors, the issue was found in the sensor’s connector—two pins had been swapped during reassembly. Correcting the pinout restored the crank signal, and the injectors began pulsing immediately. The machine started on the next crank.
This highlights the importance of verifying not just component installation, but also connector integrity and signal routing.
Preventive Measures and Rebuild Protocols
To avoid post-overhaul no-start conditions:

• Label all connectors and harnesses before disassembly
  
• Use OEM sensors and verify part numbers
  
• Test sensor output before final engine installation
  
• Scan ECU for faults before first start attempt
  
• Maintain battery charge and clean ground connections
  

For rebuilds involving electronic engines, a pre-start checklist should include sensor verification, ECU connectivity, and fuel system priming.
Conclusion
Injector pulse failure after an engine overhaul on a JCB JS160 is often rooted in crankshaft sensor issues or ECU signal interpretation. With methodical diagnostics and attention to sensor alignment, wiring integrity, and electronic protocols, technicians can restore fuel delivery and bring the engine back to life. In modern excavators, starting isn’t just mechanical—it’s a symphony of signals, and every wire plays a part.