How to check common rail injectors


How to check common rail injectors

Direct injection technology is the only one that has managed to meet the growing emission requirements. Precise dosing of fuel from the common rail by electronically controlled injectors dominates both diesel engines and gasoline units. But what if the injector is defective? In the following material, we will take a look at the available methods for diesel vehicle injection diagnostics.

Symptoms of injector faults

First we will look at the symptoms that should direct a car user to a service center for injector diagnostics. The primary symptom of an injection system malfunction is improper engine operation. Symptoms may include difficult engine starting, uneven engine operation at idle or under specific operating conditions (e.g., on a warm or cold engine, at certain rpm), noisy injectors, loss of power, excessive smoke.

A defective injector improperly doses diesel fuel into the combustion chamber, causing negative consequences for such things as excessive carbon buildup and clogging of the DPF. Driving with a faulty injection can also strain the engine mechanically, leading to premature wear of its other components.

The importance of diagnostics

We should also go to the service center if there is an error that manifests itself by lighting up the check engine light. However, it is worth remembering that this is not always the case. Diagnostics of injectors is not simple because many components affect each other and often the same symptom can have many different causes.

For example, the problem with starting the engine may relate to insufficient performance of the high-pressure pump, but the cause could also be faulty injectors. It may also turn out that the source of the problem is, for example, a clogged fuel filter, a faulty pre-pump, the wrong fuel, too low a voltage during starting (a weak battery or starter malfunction), as well as the failure of one of the sensors. A good diagnostician will effectively rule out other causes before examining the injection components.

Many people wonder to what extent it is possible to diagnose injectors at home, and although there are not many methods available in these conditions, but some measurements we can make on our car without specialized equipment.

Transfer test

Such a homemade way (also used by mechanics) is to test the overflow of injectors. The injector during operation, a certain amount of fuel taken from the common rail is not directed to the cylinder, and it flows out the so-called. Overflow and returns to the tank. This is a side effect of the injector, which, despite appearances, is a rather complex mechanism.

To make such a measurement, we need to connect the outputs of the overflows to small tanks that allow us to compare the amount of fuel. After a few minutes, we evaluate the results obtained for each injection. Funneling injectors should clearly distinguish excessive overflow from others.

Test in the system

When meeting with a mechanic, we can usually count on reading error codes and an organoleptic examination. Here a great deal depends on experience. The service technician will assess how the engine is running, pick up the characteristic rattle of the injectors, and read parameters related to the operation of the injectors, such as pressure or injector corrections. In the case of common rail injectors, diagnostics is very important because the cost of replacing injection components is significant and runs into thousands of zlotys. Simply removing the injectors involves some risk of damage to them.

What distinguishes a good diagnostician is the ability to combine different methods. There are additional, safe ways to diagnose. An example of such a solution is the measurement with the EDIA-PRO tester, which will help independently evaluate the engine’s performance. This innovative solution makes it possible to observe the parameters of operating common-rail injectors, such as injection-induced pressure drop and engine uniformity. The test is non-invasive and quick. Using such a tool we will find out which injection is knocking, and by additionally measuring the compression pressure we will also learn about the general condition of the drive unit.

Before you decide to remove the injectors for inspection, you can also check them from the electrical side. A tester that will allow you to check the injectors from the electrical side is the SIT-12. In some cases, this is enough to qualify the injector for replacement or to recognize whether the cause of the fault lies with the injector or with the wiring or controller.

Regeneration of common rail injectors

The primary method of testing injectors is to disassemble them and subject them to a test bench. Such a test not only allows you to unequivocally determine the damage to the injectors, but is also a method for confirming the effectiveness of injector regeneration.

For diesel engines, many of the injectors are repairable. Specialized services carefully assess the condition of the injectors, worn parts, such as injection tips, are replaced. In this way, damaged or worn common rail injectors are restored to efficiency , allowing them to continue to operate. An up-to-date evaluation in the form of a test report is attached to the injector. Such an injector, when installed in the car, is supposed to work like new. Well-conducted regeneration of injectors saves the customer and the environment.

GDI/FSI gasoline injectors

Although gasoline direct injection technologies work similarly to those used in diesel engines, injector remanufacturing offerings are smaller. Injector failures are less common. In the diagnosis of gasoline injectors, it is important to take into account that similar symptoms to a defective injector will give a defect in the coil or spark plug. Therefore, the injectors should be considered last.


Author: Product Engineer Piotr Libuszowski


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