Hyster H35FT Ignition Failure and Spark System Diagnosis

[MikePhua]

The Hyster H35FT and Its Engine Control System
The Hyster H35FT forklift is a mid-capacity internal combustion model designed for industrial material handling. With a lift capacity of 3,500 lbs and a compact chassis, it’s widely used in warehouses, distribution centers, and manufacturing plants. Most H35FT units are powered by a GM 2.4L or Mazda 2.0L gasoline or LPG engine, controlled via an electronic ignition system. Hyster, founded in 1929, became a global leader in lift trucks and merged into the NACCO Materials Handling Group, which has sold millions of units across North America, Europe, and Asia.
The ignition system in the H35FT is electronically managed, relying on a crankshaft position sensor, ignition control module, coil pack, and ECU (Engine Control Unit). Unlike older distributor-based systems, spark timing and delivery are handled digitally, making diagnostics more dependent on electrical testing and sensor verification.
Terminology Annotation

• ECU (Engine Control Unit): The onboard computer that manages ignition timing, fuel delivery, and sensor inputs.
  
• Crankshaft Position Sensor: A magnetic sensor that detects crankshaft rotation and sends timing signals to the ECU.
  
• Ignition Coil Pack: A module that transforms low-voltage battery power into high-voltage pulses for spark plugs.
  
• No Spark Condition: A failure in the ignition system where spark plugs do not fire, preventing combustion and engine start.
  

Symptoms of No Spark and Initial Checks
When the H35FT cranks but fails to start, and no spark is present at the plugs, the issue typically lies in one of the following areas:

• Faulty crankshaft position sensor
  
• Failed ignition coil pack
  
• Damaged wiring harness or connectors
  
• ECU malfunction or lack of power
  
• Blown fuses or relays in the ignition circuit
  

Initial steps include:

• Removing a spark plug and grounding it to check for visible spark during cranking
  
• Verifying battery voltage and ground integrity
  
• Inspecting fuses related to ignition and ECU power
  
• Checking for diagnostic trouble codes using a scan tool
  

In one case, a technician found no spark and no injector pulse, suggesting the ECU was not receiving crankshaft position data. Replacing the sensor restored both spark and fuel delivery.
Crankshaft Sensor and ECU Communication
The crankshaft position sensor is critical. Without its signal, the ECU cannot determine engine position and will not trigger spark or fuel injection. Common sensor failures include:

• Internal short or open circuit
  
• Magnetic pickup degradation
  
• Connector corrosion or broken pins
  
• Misalignment due to engine vibration
  

To test:

• Use a multimeter to check resistance across sensor terminals (typically 500–1,500 ohms)
  
• Inspect signal voltage during cranking (should pulse between 0.5–1.5V)
  
• Confirm sensor mounting and clearance to the reluctor ring
  

If the sensor is functional but the ECU does not respond, the fault may lie in the wiring harness or ECU itself.
Ignition Coil Pack and Power Supply
The coil pack receives a low-voltage signal from the ECU and transforms it into high-voltage pulses. If the coil fails, spark plugs will not fire. Coil failure modes include:

• Internal winding breakdown
  
• Heat-induced cracking
  
• Connector damage
  
• Loss of 12V supply or ground
  

To test:

• Check for 12V at the coil’s power terminal with ignition on
  
• Use an oscilloscope or test light to verify pulse signal from ECU
  
• Measure coil resistance across primary and secondary windings
  

If no power is present, trace the circuit back to the ignition relay and fuse block. In one repair, a forklift had no spark due to a corroded ground strap between the engine and frame, interrupting coil grounding.
ECU and Relay Diagnostics
The ECU must be powered and grounded to function. If the ECU is dead, no spark or injector pulse will occur. Common causes include:

• Blown ignition relay
  
• Faulty ECU ground
  
• Internal ECU failure due to voltage spike or moisture
  
• Damaged wiring harness
  

Steps to verify:

• Confirm ECU receives 12V on key-on
  
• Check ground continuity from ECU to chassis
  
• Inspect ignition relay operation and replace if suspect
  
• Scan for fault codes or communication errors
  

In one case, a technician found that the ECU was not powering up due to a failed relay. Replacing the relay restored ignition and fuel control.
Preventative Measures and Upgrade Suggestions
To prevent future ignition failures:

• Seal connectors with dielectric grease
  
• Replace worn ground straps and battery cables
  
• Mount ECU and coil pack away from heat sources
  
• Use OEM-grade sensors and coils
  
• Install surge protection for sensitive electronics
  

Technicians working in high-humidity environments should also inspect harnesses for water intrusion and consider adding protective loom or conduit.
Conclusion
A no-spark condition in the Hyster H35FT forklift is often rooted in sensor failure, coil malfunction, or ECU power loss. By methodically testing each component—starting with the crankshaft sensor and working through the ignition circuit—technicians can isolate the fault and restore engine function. In modern electronically controlled systems, spark delivery depends on clean signals, stable voltage, and robust grounding. With proper diagnostics and preventative care, the H35FT can continue serving reliably in demanding industrial environments.