Every year the share of cars with diesel engines increases. And if earlier such motors were associated with commercial equipment, now tractor engines can often be seen in small cars. Such a high popularity of diesel cars due to low fuel consumption and high torque. Due to the turbine, the power of such cars is no less than that of gasoline ones, while the consumption is one and a half to two times lower. But you need to understand that diesel is a completely different philosophy. These internal combustion engines have their own differences and repair features. In today's article, we will analyze a fairly common problem - air leaks in the diesel fuel system.
Symptoms
Usually in this situation, the engine starts well on a cold one, but further work on idle raises questions. Among the characteristic symptoms include:
- Shaking and tripling the powertrain.
- Slow response to the gas pedal.
If the problem is ignored further, a long and difficult start of the internal combustion engine is possible. Sometimes the situation comes to the point that starting a car becomes completely impossible. There is too much oxygen in the system for the mixture to ignite normally.
Causes of leakage
The causes of this problem are many. It:
- Rotten hose clamps and cracked fuel hoses. This is the most popular reason why air appears in the return of the diesel fuel system. This problem is especially relevant for owners of cars with plastic hoses. Unlike brass, they have quick couplings. Of course, replacing such a hose is much easier. However, it is the quick couplings that turn out to be the most fragile in this element. As a result of vibrations, the plastic is frayed, rubber o-rings wear out. Often a similar problem can be found on cars with mileage of 200 thousand kilometers.
- Rusty pipes, especially at the entrance to the gas tank. The problem is actual for cars with high mileage or for cars that have not been used for a long time (more than six months).
- Bad seal on the filter or booster pump.
- Violation of the tightness of the return line and the injection pump drive shaft.
- Damage to the pump cover and the axis of the diesel engine control lever.
It is possible that air in the fuel system of a diesel engine (Volkswagen or another car brand) enters through the injection pump itself. However, it is better to entrust all the diagnostic operations and repair of this pump to professionals, otherwise there is a risk of incorrectly assembling the mechanism. Among the common causes of air leakage into the diesel engine fuel system is a poor-quality filter or its loose fit to the surface. This is the most commonplace option.
It should be noted that air leaks into the fuel system of a diesel engine appear when both the forward and reverse branches are damaged. Due to the design features of the high-pressure fuel pump or engine, some of the fuel may remain in the pump, which ensures a good start. However, further work reveals characteristic problems. Motor lacks fuel, and he begins to "suffocate" without it.
How to check?
To make sure that the cause of unstable engine operation is air leaks, you need to visually analyze the flow of fuel into the cylinders. To do this, twist the starter engine for about 20-30 seconds. So we fill the exhaust tract with gases, and then we will analyze them. If the fuel system is not all right, a small amount of smoke (usually a grayish tint) will come out of the pipe. If the exhaust has a bluish-gray tint, then a large amount of oil enters the combustion chamber.
Second method
Another simple way to diagnose air leaks in the diesel engine fuel system is to inspect the traces under the bottom of the machine. If after several hours of inactivity on the floor in the garage or on the pavement, oily drops have formed, then somewhere there is a breakdown. But it often happens that there are no drips and it is almost impossible to find air leaks in the diesel fuel system in this way.
Professional diagnostic methods
The classic way to check the tightness of this system is with compressed air. To do this, you need a small amount of fuel and chalk. Last you need to rub the tubes and hoses, which moves the fuel. Next, the fuel intake is removed from the tank and the coarse filter is removed. Compressed air is supplied to the fuel intake under a pressure of not more than 0.5 kgf / cm 2 . At home, this pressure can be taken from a conventional tire chamber or wheel. Next, all tubes and hoses are inspected. Particular attention is paid to the junction. As practice shows, in 80 percent of cases the reason lies precisely here. In such areas, the chalk will darken as the fuel goes out.
Please note that damage can have a “valve” nature. That is, air can enter the system in only one direction.
Consider another method. For accurate diagnosis of air in the diesel fuel system, it is necessary to disconnect the high-pressure fuel pump from the mains and power it from a different tank with fuel. Usually a three-liter bottle and two meter durite hoses are taken. So that they do not come off, we also need clamps of appropriate sizes.
What next?
So, disconnect the hoses from the pump and install the newly purchased ones in their place. We lower their ends into a tank with fuel (it is important that it is as clean as possible and without traces of water). We fix the hoses so that they do not move, start the engine. So we find out which of the highways was damaged. It is desirable to replace the deformable element immediately.
At the end of the procedure, remove air from the fuel chamber of the pump. It is not recommended for this to simply rotate the starter.
How to get rid of air in the system?
No matter how we try to carefully replace the old hose with a new one, there will still be air in the system. But how to remove it correctly? There are several ways to pump air in the diesel fuel system:
- A container with diesel fuel is being prepared. It should be located above the level where the pump is mounted. Then we find the area where there is a "return" fitting for draining the fuel. This place should be washed well in order to prevent the ingress of dirt (the diesel fuel system is very sensitive to the smallest specks). Next, the fitting bolt is unscrewed and air is pumped out through the hole. You can pump it out with a vacuum pump (a syringe is also suitable). The operation is performed until the fuel starts to go. After that, the bolt is screwed into place, the engine starts.
- The fuel supply hose is removed from the high-pressure fuel pump and the exhausted diesel is aspirated until it starts to flow in a dense stream. After the hose is put on the union of the high-pressure fuel pump and crimped with a hose clamp. Next, the screw of the return pipe fitting is loosened. At the same time, you do not need to pump out air - it will leave on its own. Next, the engine is started and allowed to work for several minutes to completely get rid of air particles.
- The filter mounting bolt is unscrewed. The last element is not removed. Next, you need to pour a little fuel into the bolt hole. After that, the bolt is screwed into place. Loosen the union nut on the second or first nozzle. Then you need to start the engine. when the diesel starts to spray from under the nozzle nuts, they must be tightened back. This method is relevant if the cause of the leakage is a loose fit of the filter itself.
These are the main ways to remove air from the system. Please note that air can be even with serviceable fuel lines and other elements. It’s enough to drive a certain distance on a “dry” tank. Air will be automatically sucked in by the pump, and then flow to the nozzles. Do not bring the car to this state. It is advisable to refuel the car no later than the lamp on the instrument panel lights up.
Can there be a leak in other places?
It should not be excluded that air can penetrate through other places into the engine. So, after diagnosing the fuel hoses, pay attention to the intake manifold.
Thus, oxygen, which is unaccounted for by sensors (mass air flow or absolute pressure), enters the engine along with fuel, which is the cause of the unstable operation of the engine. Among the reasons, experts single out:
- Overheating, as a result of which the tightness of the gaskets is violated.
- Mechanical impact (for example, due to inaccurate repair).
- Exposure to carburetor cleaners. This is a very caustic agent that not only cleans dirt in the intake manifold, but also corrodes all rubber elements, including sealant.
The hardest thing to find is a leakage between the intake manifold and the cylinder head of the engine. Oxygen may also penetrate due to poor nozzle sealing or damage to ductwork. Consider what methods can detect the problem if it did not occur in the fuel line:
- When oxygen enters the path after the flow meter, unscrew the air pipe with the sensor from the filter housing and start the motor. At the same time, the part with the sensor is closed by hand. If there is no leakage, the motor should stall. If the engine continues to run, then there is air in the diesel fuel system (Renault Kengu is no exception). At the same time, the “sick” site will emit a characteristic hiss. The place of air leakage into the fuel system of a diesel engine must be sought by ear.
- The problem can be diagnosed by spraying probable places with mixtures of the VD-40 type. It is necessary to spray on the rubber pipe from the flow meter to the valve cover. Also spray the place where the head of the unit is connected to the intake manifold. Another area - nozzle gaskets.
About smoke generator
A more professional diagnostic method is the use of a smoke generator. But such an aggregate is often only available at service stations. The essence of the diagnosis is simple: first, smoke is introduced into the inlet tract, and then they look from what places it went outside before reaching the valve cover.
Where else to look for a reason? Tank
If the diagnostics did not give results and the fuel injectors, filter, and pump are in good condition, air can be detected through the fuel tank. But in such a situation, it is better to seek help from a service station, since it will be very difficult to check the tank for leaks with your own hands.
Conclusion
So, we examined why air appears and how to get rid of it with our own hands. As you can see, it is quite possible to eliminate air leakage in the diesel fuel system, but if the reason is serious (as we noted, this is a malfunction of the injection pump itself or problems with the tank), you can not do without the help of specialists.