31/03/2016
Understanding Common Rail System Diagnostics
The advent of Common Rail (CR) diesel technology has revolutionised fuel efficiency and emissions control in modern vehicles. However, the sophisticated nature of these systems means that troubleshooting and maintaining them requires specialised equipment. At the heart of this diagnostic process lie specialised testing units designed to accurately assess the performance of both common rail pumps and injectors. This article delves into the function and capabilities of such equipment, focusing on key components and their roles in ensuring optimal engine performance.
The Role of the Common Rail Pump Tester
A common rail pump tester is a critical piece of equipment for any garage or workshop specialising in diesel diagnostics. Its primary function is to replicate the conditions within a vehicle's fuel system, allowing for the precise measurement and analysis of common rail pump and injector behaviour. One such comprehensive system is the CRDI 786 C test bench. This robust unit is engineered to rigorously test all types of common rail injectors, pumps, and fuel rails from leading manufacturers such as Bosch, Delphi, Denso, and Siemens. It can accommodate injectors utilising both solenoid and piezoelectric technologies, offering remarkable versatility.
Key Features of the CRDI 786 C Test Bench
The CRDI 786 C is designed with the professional mechanic in mind, incorporating a range of features for efficient and accurate testing:
- Comprehensive System Testing: It can test up to two common rail injectors simultaneously, with an option to expand this capability to four injectors at an additional cost. This significantly speeds up workflow for workshops dealing with multiple vehicles.
- Fault Diagnosis: The bench is adept at diagnosing faulty common rail injectors by analysing parameters such as spray pattern, output delivery versus back leakage ratio, full load delivery, and no load delivery. It also helps identify issues with common rail pumps, including insufficient pressure generation or malfunctioning fuel metering control valves (solenoids), and excessive return flow.
- Pump Compatibility: The CRDI 786 C is compatible with a wide array of common rail pumps, including Bosch CP1, CP2, and CP3; Delphi CRSP; Denso HP0, HP3, and HP4; and Siemens DCP pumps.
- Pressure Control: Equipped with a Bosch fuel rail, pressure sensor, and a fuel rail pressure control valve/solenoid, the system allows users to precisely control and monitor fuel rail pressure, ranging from 0 to 1800 BAR. This is achieved by adjusting the solenoid's opening percentage via the integrated CRT 7000 simulator.
- User Interface and Control: The test bench comes complete with computer hardware and software, including test plans for all major manufacturers. All common rail testing parameters are managed and observed through the computer interface. The integrated CRT 7000 simulator also allows for the setting of injector pulse width (W, controlling delivery volume per spray) and spray frequency (number of sprays per second) to simulate various operational conditions.
- Safety Features: A crucial aspect of the CRDI 786 C is its shielded testing area, enclosed by an unbreakable transparent acrylic shielding box. This provides essential protection for operators from the high pressures involved during testing.
- Measurement Capabilities: Injector output delivery and return/back leakage are meticulously measured in calibrated test tubes. A dedicated rotameter is installed to accurately measure the return flow of common rail pumps. The bench also features a digital tachometer with a stroke counter, allowing users to specify the number of strokes for which readings are taken, with automatic test termination upon completion.
- Power and Dimensions: The main motor is available in 5 HP, configurable for single-phase 110V/220V or three-phase 415V, 50/60 HZ, or as per specific customer requirements. The unit has dimensions of 145 x 55 x 160 cm and weighs approximately 300 KG (net).
The Electronic Simulator CRIT 4000
Complementing the test bench is the Electronic Simulator CRIT 4000. This device is crucial for replicating the function of the vehicle's Electronic Control Unit (ECU). It generates the necessary driving signals for the injectors, enabling precise control over key testing parameters:
- Pulse Width (P): This parameter controls the volume of fuel delivered per spray.
- Frequency (F): This determines how many times the injector sprays fuel per second.
- Time (T): This sets the duration of the test in minutes.
By allowing precise manipulation of these variables, the CRIT 4000 facilitates a thorough evaluation of injector performance under various simulated operating conditions. It also includes an injector nozzle tester capable of supplying diesel to the injector at pressures up to 600 BAR. Significantly, this nozzle tester can also be used for traditional mechanical diesel injectors, allowing for the setting of opening pressures and other parameters.
Testing a Common Rail Pump with the CRDI 786 C
When testing a common rail pump, the CRDI 786 C bench provides several key measurements:
| Parameter Tested | Method of Measurement | Notes |
|---|---|---|
| Pump Return Flow | Dedicated Rotameter (Flow Meter) | Measures the volume of fuel returning from the pump. |
| Fuel Rail Pressure | Pressure Sensor on Fuel Rail, controlled via Solenoid Valve | Pressure can be set and monitored from 0-1800 BAR. |
| Injector Delivery (per injector) | Calibrated Test Tubes | Measures fuel injected over a set number of strokes/time. |
| Injector Return/Back Leakage (per injector) | Calibrated Test Tubes | Measures fuel bypassing the injector seals. |
Testing Common Rail Injectors
The process for testing common rail injectors involves using the CRIT 4000 simulator and the injector nozzle tester in conjunction with the main test bench. The key parameters assessed are:
- Delivery: The volume of fuel injected under specific conditions (controlled by Pulse Width and Frequency).
- Chattering: The audible sound produced by the injector's internal solenoid or piezo actuator, indicating its responsiveness.
- Back Leakage: The amount of fuel that leaks back through the injector when it should be sealed, measured in the calibrated tubes. High back leakage often indicates worn internal seals.
- Spray Pattern: The atomisation and distribution of fuel as it exits the injector nozzle. A good spray pattern is crucial for efficient combustion. This is visually observed, often within the shielded area.
- Output Delivery to Return Ratio: A critical efficiency metric comparing the amount of fuel injected to the amount leaking back. A healthy ratio is essential for performance and economy.
Common Rail Pump Compatibility
The CRDI 786 C test bench is designed for broad compatibility. It comes equipped with a Bosch CP1 common rail pump, coupling, and a foundation suitable for mounting various other common rail pumps. Specifically, it can test:
- Bosch CP1, CP2, CP3
- Delphi CRSP
- Denso HP0, HP3, HP4
- Siemens DCP
The bench is supplied with all necessary high-pressure pipes, electrical couplers, and adapters to connect a wide range of common rail injectors and pumps, facilitating a seamless testing experience.
Additional Resources and Support
Purchasers of these advanced testing systems also receive valuable supporting documentation. This typically includes comprehensive Equipment Operation Manuals, detailed injector test data, and an informative presentation on Common Rail technology. This ensures that technicians have the knowledge and data required to effectively operate the equipment and interpret the results.
Frequently Asked Questions
Q1: Can this test bench test piezoelectric injectors?
Yes, the CRDI 786 C is capable of testing both solenoid and piezoelectric common rail injectors.
Q2: What is the maximum pressure the system can generate?
The system can control and monitor fuel rail pressure from 0 up to 1800 BAR.
Q3: What manufacturers' pumps and injectors can be tested?
The bench is designed to test components from Bosch, Delphi, Denso, and Siemens.
Q4: Does the kit include everything needed for testing?
The test bench comes complete with all necessary high-pressure pipes, electrical couplers, adapters, computer hardware, software, and test plans for a trouble-free and speedy testing process.
Q5: Is the equipment suitable for different voltage supplies?
Yes, the power supply can be customized to work on both 110 V and 220 V, or 415V three-phase supplies as per customer requirements.
Conclusion
In summary, specialised equipment like the CRDI 786 C test bench, coupled with simulators such as the CRIT 4000, provides workshops with the essential tools to accurately diagnose and service complex common rail diesel systems. By understanding and utilising these advanced testing capabilities, technicians can ensure the longevity and optimal performance of modern diesel engines, addressing issues from injector spray patterns to pump pressure regulation with confidence and precision. The investment in such technology is paramount for staying competitive in the evolving automotive service industry.
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