Cold Testing Looked Normal

A diesel engine developed an intermittent misfire after extended operation.

When the vehicle arrived at the workshop cold, the engine ran normally.

The injector electrical checks also appeared normal.

This made the fault difficult to reproduce.

The workshop decided to test the vehicle under the same temperature condition reported by the customer.

The Fault Returned After Warm-Up

As the engine reached operating temperature, one cylinder began to drop out intermittently.

The injector itself was considered, but the workshop did not replace it immediately.

Instead, electrical measurements were repeated while the fault was present.

Heat Changed the Harness Behavior

The injector wiring showed an intermittent connection when hot.

Thermal expansion and movement around the harness affected the damaged section.

Cold testing had hidden the problem because the circuit appeared normal at lower temperature.

Why Static Testing Was Not Enough

A wiring circuit may pass a simple continuity test when the engine is stationary and cold.

However, real operating conditions add:

• heat;
• vibration;
• engine movement;
• connector stress.

An intermittent fault may only appear under these combined conditions.

Dynamic Testing

The workshop monitored the injector circuit while the engine was hot and running.

Movement of the affected harness section reproduced the cylinder interruption.

This confirmed that the electrical fault was external to the injector.

Repair Result

The damaged wiring section was repaired.

The engine was then warmed again and tested through the same operating period.

The intermittent misfire did not return.

Case Conclusion

This case demonstrates why injector electrical diagnosis sometimes needs to be performed under real operating conditions.

A cold continuity test can miss a heat-related harness fault.

When a cylinder drops out only after warm-up, technicians should consider connectors and wiring before replacing the injector.