Palau Marine Diesel Engine Develops Hot Intermittent Misfire Despite Near-Normal Injector Resistance as Current-Ramp Analysis Helps Identify Possible Solenoid Shorted-Turn Behavior

Static Resistance Did Not Match the Operating Symptom

A representative electronically controlled marine diesel case in Palau involved one cylinder that began misfiring only after the engine had been running long enough to become hot.

A basic resistance measurement of the injector solenoid appeared close to the expected range.

Because the electrical symptom remained intermittent, the workshop investigated the dynamic electrical behavior of the injector coil rather than relying only on a static ohmmeter test.

Solenoid Condition Is More Than Resistance

An injector solenoid is an electromagnetic actuator.

Its operation depends on the relationship between:

• coil resistance;
• inductance;
• current rise;
• magnetic field development;
• actuator movement;
• and ECU driver control.

A localized short between turns of the winding may alter electromagnetic behavior without producing an obvious open circuit.

Heat Became an Important Diagnostic Variable

The engine operated better when cold.

After heat soak, the cylinder fault appeared more consistently.

The workshop compared:

Cold Electrical Behavior

Injector current pattern remained relatively stable.

Hot Electrical Behavior

Current behavior changed during the fault condition.

This made the electrical comparison more relevant than a single cold resistance value.

Current Ramp Added Another Layer

Where suitable diagnostic equipment and manufacturer procedures were available, technicians reviewed the injector current waveform or current ramp.

Useful characteristics may include:

• rate of current rise;
• peak behavior;
• switching pattern;
• driver control;
• and comparison with known cylinders.

No generic current value or waveform was assumed.

The purpose was comparative diagnosis.

The ECU Driver Had to Be Separated From the Injector

An abnormal current pattern does not automatically prove the injector coil is defective.

The same symptom can also involve:

• wiring resistance;
• connector condition;
• ECU driver;
• poor supply voltage;
• or grounding.

The workshop therefore compared the suspect cylinder with another injector circuit and checked whether the abnormal pattern followed the injector or remained with the driver channel.

Why a Static Ohmmeter Can Miss the Fault

A multimeter typically measures resistance under a small test current and stable condition.

It does not reproduce:

• real injector drive current;
• switching frequency;
• heat;
• magnetic operation;
• or actual ECU pulse control.

That is why a component may appear electrically acceptable while inactive but behave differently during operation.

Case Diagnostic Logic

The investigation followed:

Cold operation acceptable → Hot misfire appears → Resistance near normal → Current ramp compared → Injector/driver separated → Electrical fault boundary established

Case Insight

The Palau case demonstrates the difference between static electrical continuity and dynamic electromagnetic performance.

For intermittent electronic injector faults, the question is not only:

“What is the resistance?”

but:

“How does the actuator behave when it is actually being driven?”

FAQ

Can an injector solenoid have a fault even if resistance appears normal?

Potentially. Some electromagnetic or temperature-dependent faults may not be obvious in a static resistance test.

Does an abnormal current waveform prove the injector is defective?

No. Wiring, power supply and ECU driver behavior also require comparison.