Common Rail Diesel Diagnostics (Troubleshoot + More)

Common Rail Diesel Diagnostics

‍Have you ever wondered how to diagnose and troubleshoot the diesel common rail system? Well, we got you covered.

Common rail diesel engines have revolutionized the automotive industry with their improved fuel efficiency, lower emissions, and enhanced performance.

However, the complexity and precision of these systems also make them more prone to failures and require a specialized approach for diagnostics and maintenance.

Here are a few steps you need to take to diagnose common rail diesel faults which include:

1. Identify the Fault Code

2. Check the Injectors

3. Check the Common Rail Pump Function

4. Confirm if a Mechanical or Electrical Pump Fault

5. Test the Injectors’ Electrical Integrity

6. Diagnose and Resolve Early Stage Lacquering

In this comprehensive guide, we will discuss the most common issues affecting common rail diesel systems and their injectors, how to diagnose them, and best practices for maintenance and repair.

Common Causes of Common Rail Diesel Injector Failures

Common rail diesel injectors are designed to operate under high pressures and with very tight tolerances.

As a result, they are more susceptible to wear and tear caused by various factors:

Particle Contamination

With clearances as small as 1 micron, even the smallest particles can cause significant damage to the injectors.

Ineffective filtration can lead to particle contamination, which can erode the control valve and ball, resulting in a poor seal and altered fuel spray patterns.

Over time, this can affect the quantity, timing, and distribution of the injected fuel.

Water Contamination

Water contamination is another common cause of common rail injector failure. Diesel fuel is hygroscopic, meaning it absorbs water from the atmosphere.

When not stored or handled correctly, water can enter the fuel and react with the chemicals in it, leading to the corrosion of metal surfaces and reduced lubrication between moving parts.

This can cause premature wear of both the injectors and the high-pressure fuel pump.

Deposit Build-up

Carbon deposits, also known as coking, can form around the nozzle tip and the injector’s internal parts when fuel is left in the injector after the engine shut down.

This can cause the needle to stick, disrupting both the quantity and timing of the injection.

Incorrect Installation

Poor installation practices can also contribute to premature failure. For example, a missing nozzle washer or one that has not been properly seated will allow combustion residue to leak past the nozzle washer.

Similarly, seal rings can easily roll out of their grooves. These seemingly simple issues can result in more significant problems, including poor injector performance, starting difficulties, and reduced fuel efficiency.

Read also >> How Does A Common Rail Diesel Fuel System Work? (Incl. Video)

Read also >> What Does Common Rail Diesel Engine Mean? (Benefits + More)

Read also >> Common Rail Diesel Not Holding Pressure (Here Is What To Do)

Read also >> Common Rail Diesel Injection: The Future of Fuel Efficiency and Engine Performance

Symptoms of Faulty Common Rail Diesel Injectors

A faulty common rail diesel injector can cause a wide range of issues, including:

  • Check engine light
  • Rough idle
  • Engine knock
  • Engine surge
  • Engine misfire
  • Fuel leakage
  • Poor fuel economy
  • Increased emissions

To pinpoint the exact cause and perform a thorough diagnosis, it is crucial to follow a systematic approach and use the correct diagnostic tools.

Diagnosing Common Rail Diesel Injector Issues

Follow these steps to accurately diagnose common rail diesel injector issues:

1. Identify the Fault Code

Use a high-quality diagnostic tool, like Delphi Technologies’ DS solution, to interrogate the vehicle’s OBD system and identify any fault codes related to the fuel injection system.

2. Check the Injectors

If the OBD has generated a fuel injection system fault code, check the injector’s functionality using tools like Delphi Technologies’ Sealed Rail Diagnostic Kit.

This kit connects to the injectors and collects and measures back leakage flow, indicating which injector may be faulty and in need of replacement.

3. Check the Common Rail Pump Function

Fit the Sealed Rail Kit directly onto the high-pressure outlet pipe from the pump and crank the engine to record pressure in the system.

If the pressure measurement differs from the specified value for the vehicle application, the pump may be faulty.

4. Confirm if a Mechanical or Electrical Pump Fault

Use Delphi’s False Actuator Kit in conjunction with the Sealed Rail Kit to determine if the common rail pump has a mechanical or electrical fault.

If the pump generates the correct pressure with the False Actuator in place, the vehicle actuator may be faulty.

If the pressure is still below the required level, the common rail pump may have a mechanical fault.

5. Test the Injectors’ Electrical Integrity

Use Delphi Technologies’ Electronic Injector Test Kit to test for open coil circuits, coil internal short circuits, and coil insulation to the injector body, and measure the coil’s resistance and inductance.

This will help identify any electronic failures in the injectors.

6. Diagnose and Resolve Early Stage Lacquering

If no faults are identified during the previous tests, valve lacquering may be present.

Perform a ‘buzz’ test using the Electronic Injector Test Kit to check if the injector is moving freely.

If not, use the Injector Solvent Cleaning Kit to clean any lacquering on the valve.

Replacing a Common Rail Injector

Once you’ve identified the faulty injector, follow these steps for a best practice replacement:

  1. Check for residual pressure in the system using a diagnostic tool.
  2. Remove the injector pipe and cap any exposed pipes to prevent contamination.
  3. Remove the back leakage, electrical connector, and holding clamp, and withdraw the injector from the seat.
  4. Note the new correction code of the replacement injector.
  5. Carefully slide the new injector into position and refit the retaining clamp, torquing to the manufacturer’s specifications.
  6. Refit the electrical connector and back leakage.
  7. Install a new high-pressure pipe and torque to the correct specifications using proper tooling.
  8. Reprogram the ECU with the new correction code using a diagnostic tool to ensure correct fuel delivery.

Common Rail Diesel – No Start Fuel System Basics >> Check out the video below:

Maintaining Common Rail Diesel Injectors

Regular maintenance is essential to keep common rail diesel injectors in good working order:

  • Inspect injectors regularly, ideally every 20,000 miles.
  • Use premium quality fuel with added detergents to keep engine parts clean from deposits.
  • Periodically add a fuel system cleaner to maintain the fuel injection system.
  • Change engine oil regularly to ensure optimal engine efficiency.
  • Replace air, oil, and fuel filters regularly to prevent contaminants from entering the engine.
  • Consider driving style, as shorter start-stop journeys and hard driving can increase wear and tear on the fuel injection system.

By following this comprehensive guide, you can efficiently diagnose and resolve common rail diesel injector issues, ensuring the best performance and longevity for your customers’ vehicles.

Stephan K.

I have been working as a mechanic for over 13 years and have been deeper into advanced automotive diagnostics for some years.

Recent Posts

error: Content is protected !!