Diagnosing No-Start Issues in a 1994 Western Star 4964FX with Detroit Diesel Series 60

[MikePhua]

Western Star 4964FX and Detroit Diesel Series 60 Overview
The 1994 Western Star 4964FX is a heavy-duty vocational truck built for long-haul and construction applications. Western Star, founded in 1967, became known for its rugged, customizable trucks tailored to owner-operators and fleet buyers alike. The 4964FX model was often equipped with the Detroit Diesel Series 60 engine, a revolutionary inline-six introduced in 1987 that became the first fully electronically controlled heavy-duty diesel engine in North America.
The Series 60 engine, particularly the DDEC III and DDEC IV variants, featured electronic fuel injection, onboard diagnostics, and a programmable ECM (Engine Control Module). These innovations improved fuel economy and emissions compliance but introduced new layers of complexity in troubleshooting.
Symptoms of a No-Start Condition
In one case involving a 1994 Western Star 4964FX, the truck would crank but not fire. The fuel system had already been bled and verified, eliminating air intrusion or fuel starvation as the cause. This pointed toward an electrical or ECM-related issue.
Key symptoms included:

• Engine cranks normally but does not start
  
• Fuel pump operational and system primed
  
• No check engine light (CEL) illumination with key on
  

The absence of the CEL is a critical clue. On DDEC-equipped engines, the CEL should briefly illuminate during key-on as the ECM powers up. If it does not, the ECM may not be receiving power, or the ignition circuit may be compromised.
Common Electrical Faults in DDEC Systems
The Detroit Diesel Electronic Control (DDEC) system relies on a stable 12V or 24V power supply, depending on configuration. Power is typically routed through fuses and relays located in or near the battery box.
Frequent causes of no-start conditions include:

• Blown ignition fuse: Often located in the battery box or under the dash
  
• Disconnected or corroded ECM power leads: Especially common in older trucks with exposed wiring
  
• Loose or damaged harness connectors: Particularly the ECM-to-battery harness
  
• Failed ignition relay: Prevents ECM from receiving switched power
  

One operator reported a similar issue caused by a loose fuel return line at the rear of the cylinder head. When the head drains of fuel, the engine will crank but not fire, mimicking an electrical fault. This highlights the importance of checking both mechanical and electrical systems in parallel.
Diagnostic Steps and Tools
To isolate the problem:

• Check for CEL illumination with key on
  
• Use a multimeter to verify voltage at the ECM power pins
  
• Inspect all fuses related to ignition and ECM circuits
  
• Confirm ground integrity at the ECM and battery terminals
  
• Use a diagnostic reader compatible with DDEC III or IV to check for stored fault codes
  

If the ECM is not powering up, trace the power supply from the battery through the ignition switch and fuse panel. In some cases, the ECM harness includes a weather-sealed inline fuse that may be overlooked.
Wiring Diagrams and Technical Resources
Access to accurate wiring diagrams is essential. For DDEC III and IV systems, the ECM typically has three main connectors:

• Power and ground
  
• Sensor inputs (e.g., coolant temp, oil pressure)
  
• Actuator outputs (e.g., injectors, Jake brake)
  

Color-coded diagrams can help trace circuits and identify faults. Technicians with access to Detroit Diesel’s Diagnostic Link software can also perform live data monitoring and ECM reprogramming.
Conclusion
A 1994 Western Star 4964FX with a Detroit Diesel Series 60 that cranks but does not start is most likely suffering from an ECM power issue, especially if the check engine light fails to illuminate. By methodically inspecting fuses, harnesses, and grounds, and using proper diagnostic tools, the root cause can be identified and resolved. These older electronic engines, while more complex than their mechanical predecessors, remain serviceable with the right knowledge and resources.