Diagnostics and cleaning of fuel injectors

Very often, a motorist has to deal with increased fuel consumption, a drop in power, and sometimes with a complete refusal of the car to move. The most common cause of this is a malfunction of the fuel injectors due to the use of fuel of inadequate quality. And it does not matter whether this is caused by the desire of the driver to save money on cheaper fuel or the dishonesty of the employees of gas stations. One way or another, there is a problem of the need to replace the nozzles. Simplest (and without a doubt the best) the way out in this case is to contact the nearest specialized service station. However, if the owner of the car believes that he is able to cope with the problem on his own, certainly saving some money at the same time, the following tips are given to help him, which will either help the motorist avoid mistakes in the process of work, or convince him of the timely abandonment of a useless undertaking.

First of all, it is necessary to clearly realize that, the process of replacement itself (described in the relevant chapter of this manual) should be performed only with certain skills, since it can be fraught with certain dangers for both health and human life - fuel pressure in some injection systems of modern engines can reach 250 atm, so any carelessness can have fatal consequences.


The second, no less important point is that even in the case of a successful replacement of the fuel injector, there is a danger of getting an injector with an atomization of much worse quality than it was before the replacement, even if the quality of the replaced parts is the highest. What can we say about cases of using low-quality or defective nozzles. It is in order to avoid such situations that it is necessary to use special diagnostic stands available at service stations, or at least the simplest device, which will be discussed below.

First you need to understand the device of a diesel nozzle and understand the processes occurring in it. All nozzles, with rare exceptions, are fundamentally similar, and the processes occurring in them are similar. The fuel injector device is shown in the figure.




The principle of operation of the fuel injector is as follows: fuel from the high pressure pump (injection pump) enters the nozzle nozzle, and from there through the channel system (12) into the atomizer (7). Further advancement of the fuel is closed by the atomizer needle (6), compressed by a spring (13). Meanwhile, the injection pump continues to pump fuel, raising its pressure to a value that can overcome the spring force and lift the atomizer needle above the seat. In this case, fuel is injected into the cylinder, as a result of which the pressure drops again and the needle sits on the seat, cutting off the fuel supply and locking the system. The process repeats as the fuel injection continues. The main condition for this is that after the end of the injection, the system must close, otherwise, on the next stroke, fuel will be supplied not when the pressure in the system rises to the set value, but at the moment the pump starts supplying fuel. The consequence of this will be hard engine operation, loss of power and failure of the fuel injector due to the ingress of combustion products into an unlocked system.

Knowing the principle of operation of the nozzle, you can figure out what can interfere with the normal locking of the system with externally serviceable parts. The most common reason for this is the occurrence of lateral forces pressing the needle against the body of the atomizer. To combat such forces, there is a push pin (14), placed in spacer (4). The pin unloads the needle from the possible impact of a deformed spring, however, if there is some wear on it, the pin itself can cause a lateral force. Therefore, when replacing fuel injectors, you need to be prepared for the fact that the new atomizer will start «pour», which will require repeated reassembly of the nozzle with turning the spring over or replacing it or the pusher. In some cases, it may even be necessary to replace the fuel injector housing.




Since the needle in the atomizer is not sealed with anything, a certain amount of fuel seeps between the needle and the nozzle body and enters the cavity where the spring is located (13). If the fuel is not removed from this cavity, the atomizer needle may lose its ability to move and the nozzle will be «locked». A drainage system is used to remove leaked fuel (10).

Needle opening pressure adjustable with shims (11), and the whole structure is tightened with a union nut (4).

No sealing elements are provided in the nozzle, and tightness is ensured exclusively by precision machining of the mating surfaces. As a result, there is a basic requirement when working with fuel injectors - sterile cleanliness.

Immediately after unscrewing the high-pressure pipeline from the nozzle, it is necessary to close the nozzle nozzle with a clean and tight cap, since the smallest debris that has fallen into the nozzle nozzle during the test on the bench will be driven in by fuel and can jam the atomizer needle. The cavity of the nozzle must always, even before checking and adjusting, even after, be absolutely protected from the ingress of any dust, not to mention larger particles. In addition, any dirt when removing the nozzle can enter the channel and then damage the threads or break the seat seal.


It is advisable to remove high-pressure pipelines in a package along with screeds (the engine design permits this), so less reason to puzzle over tyam, as it all stood. If it is impossible to remove the pipelines in a package, it is necessary to mark the fitting of the first cylinder on the pump, and also mark the pipelines themselves in the order in which they stood.

After removing the injectors, it is necessary to check their performance in order to make sure that the alleged cause of the engine malfunction is correct.

The check criteria are as follows:

• When fuel is supplied, the nozzle must open at a predetermined pressure.
• Before opening the nozzle, fuel leakage from the atomizer is not allowed.
• At the moment of fuel spraying, drops and jets are unacceptable.
• The spray pattern must be even without deviations and correspond to the direction of the hole (or holes) in the sprayer.

After the fuel supply is cut off, the pressure must remain in the injector for some time (strictly speaking, the rate of fall of this pressure must be controlled).

The amount of fuel sprayed by the injectors of different engine cylinders must be the same.



It is also customary to talk about the characteristic sound of injector operation, but the sound is not an objective parameter for evaluating injectors. You can’t ignore this parameter, but you shouldn’t make it the main one either.

Undoubtedly, it is best to check the performance of the injectors on a special stand. Design (and, accordingly, the cost) such a stand can be the most diverse, which will undoubtedly affect the accuracy of diagnostics and ease of use. Service stations can use electronically controlled stands costing several thousand dollars, however, if the car owner is determined to diagnose the injectors himself, we can recommend making the simplest stand on your own.

To do this, it will be necessary to make a tee pipeline, which at one end will be connected to one of the high-pressure fittings of the injection pump, the other to the fuel injector, and at the third end it is necessary to fix a pressure gauge with a scale of 200-300 atm.



A measuring vessel must be placed under the nozzle sprayer (beaker).

Scrolling the engine with a starter, you need to ensure that the nozzle starts «fire», after which, leaving the ignition on, the engine dip reading the pressure gauge (tedious process, but perfectly acceptable in the absence of other options).

In the vast majority of modern injectors, the opening pressure is controlled by selecting the thickness of the spacer between the spring and the housing. Specialty workshops have sets of these washers to solve any adjustment problem. For motorists, it should be borne in mind that washers exist in various diameters (for various nozzle bodies), and are available with or without a hole. Washers without holes can always be used instead! washers with a hole, but reverse replacement is not allowed. It is also unacceptable to use washers of the wrong diameter.

As a rule, nozzles are designed in such a way that an increase in washer thickness by 0.1 mm leads to an increase in injection pressure by 10 atmospheres (10 kg/cm² or 980 kPa). It is very common to see when repairing injectors that during previous interventions, the injection pressure was regulated using pieces of razor blades placed under the spring. This type of regulation is completely unacceptable. Firstly, having a gasket of an uncontrolled shape creates an uncertainty in the spring support and, thereby, its inhomogeneous development, which provokes the occurrence of lateral force. In addition, there is a risk of chipping a piece of the blade, which will lead to a complete failure of the nozzle. The use of metal foil is also acceptable, since pads made of soft material are completely short-lived. Therefore, the only qualitative solution to the problem should be the use of new adjusting washers of the calculated thickness.

Flushing and cleaning fuel injectors at home is strongly discouraged due to the pointlessness of the undertaking.