These devices at a certain dosage inject fuel into the combustion chamber, where the air is heated to high temperatures and high pressure is created. The nozzles are subjected to the highest loads - the mechanism constantly works in aggressive environments, and the work itself is associated with high intensity. Therefore, injectors often fail. Diesel injector diagnostics is the first thing you need to start repairing fuel equipment and only then move on to other elements.
Diesel injection principle
For a better understanding of the mechanism of the injector, it is necessary to describe the injection cycle in a diesel engine.
So, the injection pump takes a certain amount of diesel fuel from the fuel tank. Next, the pump pumps fuel into the rail. Diesel fuel is fed into the channels leading to the nozzles. The fuel is then fed to the atomizers. When the pressure level on the atomizer reaches a certain level set by the manufacturer, the nozzle opens and diesel fuel is supplied to the cylinders.
How a diesel injector works
On the example of a primitive nozzle, you can consider the principle of operation. In the side part there is a channel through which diesel fuel is continuously supplied. Inside the nozzle there is a chamber - it has a barrier. It can move due to the spring. There is also a needle in the device. The barrier can move down or up as the pressure rises/falls. The needle can rise under pressure, thereby clearing the way for fuel. This is how a primitive nozzle with one spring works.
Two types of nozzles are installed on power units with this power system - these are electromagnetic and piezoelectric. The latter is a very serious mechanism, it is compared with Ferrari cars, and the analogy is not accidental, given the frequency of operation. In order to facilitate the diagnosis of diesel injectors in case of malfunctions, one should understand its structure and principle of operation.
The electromagnetic nozzle is a body with a solenoid inside, a multiplier valve, a plunger that acts on a needle in the atomizer body. All this is complemented by inlet and outlet channels for fuel.
It all works as follows. Diesel fuel is supplied through the high-pressure channels from the rail to the needle where it contacts the atomizer and into the cavity above the plunger. Due to this, the plunger presses the needle to its seat. At the right moment, the solenoid will rise and open the valve - the cavityabove the plunger will connect to the drain channel. Since the pressure above the plunger decreases, and around the needle increases, the needle rises due to pressure and fuel is injected. As soon as the solenoid returns to its rightful place, the pressure over the plunger returns to normal and the needle closes instantly.
The piezoelectric injector works in much the same way, but it's a different device. The design of the mechanism has an additional hydraulic compensator - it is an intermediary between the piezoelectric element and the multivalve. In general, the parts are almost the same as those found in the electromagnetic injector.
The beauty is that when electricity is applied to the piezoelectric element, it changes its characteristics and geometry in just 0.1 ms. This speed of operation makes it possible to divide the injection cycle into several processes, while maintaining such an accurate dosage that even a gram of diesel fuel will not be wasted.
For better understanding
One fuel injection cycle is divided into three parts - this is the preliminary injection, the main phase and the final one. So, during the preliminary part, only a small part of the fuel is supplied to the cylinders - something within 2 ml. This is necessary for warming up and preparing the air in the combustion chamber in the supply of the main portion of the fuel. At the same time, the pressure inside the cylinder equalizes. The main phase is understandable, and there is no need to describe anything further. But the injection of a small portion in the final phase is needed to burn out the remaining mixture in the cylinder. This contributes to better cleaning andparticulate filter regeneration.
The advantages of piezo injectors are that in one cycle it is able to supply fuel several times. Thanks to this, the engine runs very smoothly and is almost impossible to distinguish from its gasoline counterparts.
What usually breaks down in solenoid injectors
Start with electromagnetic mechanisms. The main and worst enemy of any injectors is bad fuel and water. But of course, in the process of diagnosing diesel injectors, natural wear is also observed.
The most common malfunction is the wear of the seat for the multiplier ball. If the plunger is not tightly closed, then this leads to the fact that diesel fuel flows into the drain line. If sufficient pressure is not created over the plunger, then fuel leakage through the atomizer is possible. If there are no leaks through the sprayer, but there is a leak through the drain channel, then the engine will stall under load. If the needle shrinks, shrinkage of the plunger is observed, if the needle is not adjusted or it does not exist at all, then this will lead to overflow. The motor will troit, at idle white smoke is possible from the pipe. If we carry out diagnostics of Common diesel injectors, then, most likely, these shortcomings will be identified.
Losing stiffness and the spring pressing the needle. Due to corrosion, the multiplier wedges. There are also problems with the solenoid that opens the intake valve - all this does not add stability to the engine in operation.
Each part in the nozzle is subjected to one or another negative impact, and even a minor detail can lead to unstable operationengine.
Faulty piezo injectors
As for malfunctions, everything here is approximately the same as for devices of outdated design. But due to a more complex control element, you can add a short circuit to the "mass" of the piezoelectric element. This may result in the engine simply not starting.
The malfunctions of the needles and sprayers are mentioned above, but it must be added that if the nozzle overflows strongly, then black smoke will smoke strongly from the exhaust pipe. This is a signal for the diagnosis of diesel injectors.
It happens less often that the piezoelectric element fails or loses its properties. In case of loss of properties, the motor may lose traction and triple. It is necessary to mention coking.
How injectors are checked in service stations
When complaining about the smoke of the internal combustion engine, loss of traction and other symptoms described above, the first step is to perform computer diagnostics. And if the system generates errors during the process, the elements are dismantled and transferred to the workshop for further diagnostics of diesel injectors at the stand.
The element is installed on the stand, where they check the basic performance - whether the fuel is poisoning through the drain line, if there is a leak, then under what pressure it occurs. If the diagnostics on the stand shows that everything is in order, then the element is installed on more serious equipment, where the operation of a diesel engine is almost completely simulated. In the course of such diagnostics of the operation of diesel injectors, automation will gradually measure all the parameters and characteristics of the injector, thiswill give an understanding of the causes and problems.
Next, the nozzle is sent to the ultrasonic bath in order to remove carbon and coke. Next, the part is sent to a special stand, where it will be dismantled for subsequent repair.
You can do your own diagnostics of Common Rail diesel injectors. There are two ways to do this - checking the injectors on a ramp and a makeshift stand, checking on the engine.
Judging by the reviews, the easiest way to test the operation of the injectors on the motor without removing it. To do this, the engine must be idling. Then the owner must unscrew the atomizers in turn. If, after removing the atomizer, the operation of the motor has become worse, then the nozzle is working. So by the elimination method, you can find a non-working nozzle - when you unscrew the sprayer, the engine will not change.
You can also check the injectors for leaks directly on the engine. To do this, you will need special plastic containers and connecting hoses. The hoses are connected to the nozzles. Containers should be hung vertically.
Then start the engine and start watching. If one of the prepared transparent containers fills up faster than the others, then that's the problem. When analyzing injectors, make sure that the containers are not more than three-quarters full. The norm for such testing is a difference of 10%. If the difference in fuel volume is greater, then you need to look for a leak.
This diagnostic method is simple and effective, but the problem is not always associated withleaks.
This is how diesel injector diagnostics are performed. Repair involves ultrasonic cleaning, as well as the replacement of worn parts. Check each washer, solenoid travel, retaining rings, measure all bushings. Everything that is worn out is replaced with new.