Cold Testing Found Nothing

An Australian diesel workshop received a vehicle with an intermittent cylinder misfire.

When the engine was cold, the injector operated normally.

Electrical checks also appeared acceptable.

After the vehicle had been driven, switched off briefly, and restarted, the cylinder fault returned.

This made temperature an important part of the diagnosis.

Heat-Soak Testing Reproduced the Fault

The technicians warmed the engine fully and allowed it to remain stationary after shutdown.

Under-hood temperature continued to rise for a period even though the engine was no longer running.

When restarted, the same cylinder began to misfire.

The injector connector and wiring were then tested while hot.

Resistance Changed Under Temperature

The workshop found that electrical resistance in the affected circuit became unstable when the components were hot.

At lower temperature, the connection behaved normally.

This explained why previous cold continuity testing had failed to find the problem.

The Injector Itself Was Not Replaced

The affected electrical connection was repaired.

The vehicle was then subjected to the same warm-up, shutdown, and restart sequence.

The cylinder continued operating normally.

The injector remained in service.

Australian Heat Context

In high ambient temperatures, engine-bay heat soak can expose weak electrical connections that remain hidden during a cold workshop test.

For Australian diesel applications, temperature should therefore be treated as a test condition rather than background information.

Case Conclusion

This case shows why electrical injector testing sometimes has to be performed hot.

A circuit that passes a cold resistance or continuity test may behave differently after thermal expansion.

Reproducing the temperature condition prevented an unnecessary injector replacement.