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Common Rail Testing Instruments From Bosch

Posted on 9/23/2016 3:58:17 PM

Whenever Common Rails develop a problem, it’s vital to check their high- and low-pressure circuits. To this end, the diesel specialists at Bosch have developed a whole number of test instruments.As diesel injection parts suppliers in Aftermarket,China Balin Power Co.,Ltd will introduce more details here.
As with every electronically controlled vehicle system, service diagnostics on diesel engines with Common Rail injection begin with readouts of the fault store and analyses of their data. If electrical problems are detected, they need to be checked for plausibility and fi xed in line with manufacturer specifi cations. Symptoms and fault recordings indicating a malfunction in the fuel system require tests of the low- and high-pressure circuit prior to component replacements. These tests prove helpful in the majority of cases, even when an ECU shows no fault entries at all despite poor engine performance. Determining which part of the system to test first – the high- or the low-pressure circuit – depends on the nature of the problem and on accessibility to the fuel system. Either way, the specialist should always remember that irregularities in the low-pressure circuit directly affect the generation of high pressure. Prior to opening the fuel system, workshop exerts also need to observe all sanitary guidelines regarding the treatment of high-pressure diesel systems. That’s because even the tiniest of dirt particles entering a fuel system can result in costly damage.
Testing Low-pressure Circuits
The low-pressure circuit comprises the fuel line from the fuel tank to the high-pressure pump and fuel return. The fi rst step is to check all lines for air tightness or damage, as well as the condition of the fuel fi lter. If the pressures measured before and after the fi lter show a difference greater than 0.3 bar, then the fuel fi lter needs to be replaced. The next step for the specialist is to test the pressure in the forward delivery and return of fuel by means of a proper manometer and to compare them to manufacturer specifi cations. The forward-delivery pressure is measured in the line between the fuel fi lter and the high-pressure pump. Electric fuel pumps have to supply pressure ranging from 2.0 to 2.5 bar during the start-up. Systems using gear pumps (CP1 H and CP3) should deliver pressure between -0.10 and -0.20 bar in forward delivery. In first-generation Common Rails, the fuel return pressure is the decisive factor in opening the safety valve in the high-pressure pump. It is measured between the return collection pipe and the fuel tank and should deliver between 0.6 and 0.9 bar. Third-generation Common Rails with Bosch piezo injectors deliver a return pressure of 10 bar. This pressure determines the proper operation of the injectors. For all low-pressure circuit tests, Bosch offers Diesel Set 1. This very universal test box provides workshop exerts with a variety of testing adaptations for lowpressure circuits of virtually all Common Rail systems on the market. The Y-adapters of the test set have a transparent fuel line allowing workshop exerts to see whether fuel is sent to a highpressure pump without any bubbles.
High-pressure Testing
In order to allow vehicle specialists at the diesel service to diagnose the condition of high-pressure pumps and Common Rail pressure sensors without removing them in the course of diesel service, Bosch has developed Diesel Set 3. It enables them to test the performance of highpressure pumps during start-up in real conditions. They can also use it to measure Common Rail pressure regardless of ECU diagnostics when the engine is running. Diesel Set 3 consists of a pressure sensor module, a pressure sensor and a digital pressure display. The set also comes with special high-pressure test lines and numerous fl exible adaptations for virtually all systems on the market. Testing the high-pressure pump during start-up is especially useful when dealing with start problems. In this case, a test line is used to connect the pressure sensor module directly to the outlet of the high-pressure pump and then the engine is started. After a few seconds, the workshop expert can read the actual pressure on the display unit. An intact highpressure pump by Bosch should have a pressure greater than or equal to 250 bar. The pressure sensor module has an overfl ow valve limiting pressure to 500 bar. Along with the over- fl ow valve, the module also comes with an installed calibrated leakage throttle simulating the fuel intake of the injectors as the engine is started. That way, the module measures not only the pressure of the high-pressure pump, but also its pump capacity at starting speed. Testing Common Rail pressure with Diesel Set 3 involves removing the high-pressure delivery line of an easily accessible injector and connecting the pressure sensor directly to the Common Rail via a test line. A pressure connection for the injector is available as an option. After starting the engine, the workshop expert can compare the displayed pressure readout with the corresponding actual value from the ECU diagnosis and thereby test the high-pressure sensor. If the actual value and the measured Common Rail pressure differ from each other, then the Common Rail pressure sensor needs to be replaced.
Comparing Leak-fuel Quantities
The software of the KTS Diagnosis Testers of Bosch contains very practical functional tests that workshop exerts can utilize for customer requests to diagnose defective injectors. Before an injector is replaced, however, the results of the ECU diagnosis always have to be checked for plausibility by performing a leakfuel quantity comparison test. For the latter, Bosch offers a leak-fuelquantity measuring device for easy mounting in the engine compartment. This device comprises small doubletier test tubes embedded in a solid plastic block. Bosch piezo injectors require an additional special adaption with pressure-holding valves that maintain a pressure of ten bar in the return lines. The quantity-measuring device is directly hooked up to the return connection of the injectors. When removing the return line on the injector, be careful not to damage the connection. Disconnecting the line to the fuel injector also requires proper means of doing so without damaging it. Once the return-quantity measuring device is hooked up, the engine is started and the return quantity is measured on all cylinders. Here it is important that the quantities of the individual cylinders increase at the same rate. Bosch systems compensate for any difference of up to about 24 ml by means of solenoid valve injectors. Any difference higher than that requires the injectors with the largest return quantities to be either repaired or replaced.

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