The fuel systems of modern car engines are complex systems of mechanisms and assemblies. Among them there are systems that can only be operated by a specialist. However, simpler systems, such as those found, for example, in older VAZ car models, can be more difficult to repair than systems in modern cars. Failure of even the smallest parts of the fuel system can seriously impair the performance of the vehicle. The fuel system check valve is no exception. But, before starting any repair work, you need to find out about the structure and functions of this unit.
Check valve functions
The fuel pumps of modern cars have high performance and, with proper care, provide a continuous supply of fuel, regardless of the load being generated. It is impossible for the engine to operate at idle speed without a fuel system check valve.
Moreover, this unit is present not only in gasoline engines with a carburetor and in injection engines. The check valve for the fuel system of a diesel engine is also an indispensable part of the fuel system of such engines.
The main purpose of this valve is to prevent the build-up of too high pressure in the fuel system, which could result in the fuel hoses breaking. In principle, the purpose of any valve is to allow the movement of different fluids in one main direction. Located in the fuel system, this valve prevents a number of problems that can arise in the system as a result of broken hoses.
For example, if you are driving a car with a diesel engine, then a breakdown of the check valve along the way can cause the fuel system to begin to fill with air. The presence of air is also unacceptable in injection power systems.
If the driver stops the engine, while fuel flows into the tank along the working line, then the vacated space is quickly filled with air. In such situations, you will have to turn the engine with the starter for at least fifty seconds.
Work order
- First, disconnect the negative terminal from the battery (key to “10”).
- Disconnect the regulator vacuum hose from the intake manifold fitting.
- Using a “17” wrench, unscrew the nut securing the drain hose. Disconnect the hose.
- Using a Phillips screwdriver, unscrew the bolt of the return pipeline clamping plate.
- Using a hex wrench set to “5”, unscrew the screws securing the RTD to the fuel rail.
- Using a “24” wrench, unscrew the nut connecting the drain hose fitting and the RTD.
- Remove the fuel pressure regulator.
That's basically the whole process.
Installation of the RTD is carried out in the reverse order. Important: do not lose the rubber seal that comes with the regulator. Without it, the connection between the RTD and the fuel rail will be leaky, which will lead to a change in the operating pressure in the system
Device and principle of operation
The check valve device is simple. The entire mechanism consists of a spring, a membrane and the valve itself. The ball-type valve is equipped with a special seat, which is made of soft metal and is calibrated as accurately as possible.
The valve body is equipped with three outlets: the first is for the intake manifold, and the others are for fuel removal. Fuel moves freely through the valve in only one direction.
It is not able to flow back into the valve due to the pressure created on it, which is why it closes. The valve opens due to the movement of the spring resulting from the vacuum as the engine speed increases. Excess fuel is returned back to the fuel tank.
The fuel system valve is often confused with the pressure reducing valve. To avoid this, read the vehicle's operating instructions in detail. The pressure reducing valve is used in injection and diesel engines and operates in parallel with the check valve of the fuel system.
The check valve for diesel fuel is no different in operating principle from its “brother” used in gasoline engines; differences can only arise in the location of this unit.
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Reference
Many people know that the fuel system valve aggregates:
There is nothing complicated about the mechanical design. This is a ball-type device with a seat, which is made of soft metal, with the most accurate balancing. Fuel flows freely through the fuel valve in one direction. The pressure that is created prevents gasoline or diesel fuel from flowing back into the fuel tank, since the non-demountable structure is locked.
Despite its simplicity, the device can cause a lot of trouble for a novice and an experienced driver. Therefore, it is necessary to know its possible vagaries and ways to eliminate breakdowns. But first of all, understand where the mechanical structure is installed.
“The concept of a fuel system check valve should not be confused with a pressure reducing device.”
Location
Where is the fuel system check valve located? You can find this parameter in the instructions, but most often this valve is attached to the fuel rail in the housing. The fuel rail is a metal structure onto which, in addition to our valve, the injectors responsible for injecting fuel into the engine are also attached.
In some ramps, the check valve is screwed into the end with a thread. On some vehicles it may also be located between the fuel tank and the injectors in the fuel line.
In diesel vehicles, due to the fact that the pressure at the inlet of the injection pump (high pressure fuel pump) must remain stable, a check valve is attached between the low pressure hand pump and the injection pump. If the car has a special fuel preheating system, then a check valve is installed in front of this system.
Fuel system check valve malfunction
Symptoms of a problem
There are several characteristic signs that may indicate a malfunction of the check valve:
- The engine runs unsteadily and intermittently at minimum speed.
- The engine starts only after a long rotation of the starter while simultaneously pressing the gas pedal.
- Gasoline leaks from the fuel hoses and continues to leak after replacing them and tightening the clamps.
- The speed changes sharply at idle.
Due to the fact that the design of the check valve is completely mechanical, its diagnosis using special instruments is impossible. It will not be possible to disassemble the check valve and repair it, since its entire structure is quite cheap, and there are no individual spare parts on sale.
You can find out whether the valve is working properly by measuring the pressure in the fuel system with a pressure gauge. To do this, connect the pressure gauge to the section that supplies power to the engine. A rapid decrease in pressure when the engine is stopped will indicate a valve malfunction.
Another way to check the valve's functionality is to monitor the pressure level when the return hose is pinched. The pressure should increase, but this method is not suitable for all cars, since in some of them these hoses are made of metal.
If the engine runs erratically, clamp the return hose and observe the engine again. If the required power is gained at this moment, and the cylinders are functioning, you can safely change the valve.
Basic faults
The main malfunction of a check valve is failure due to long-term use. Any car part has its own expiration date, after which, even with proper handling, it will no longer function as before.
Other common valve malfunctions are mechanical damage or blockage, which occurs, for example, due to the use of low-quality fuel. Most often, the spring and membrane wear out.
Causes of malfunctions
Why does the valve fail? Recently, the auto parts market has been flooded with cheap Chinese parts. Quite often such spare parts fail due to manufacturing defects. The check valve is no exception.
As mentioned above, wear and tear is often caused by time and poor quality fuel. If gasoline or diesel fuel is mixed with water, then such a mixture will be destructive for many units of the fuel system.
Valve clogging as a result of using low-quality fuel can also be a significant cause. Clogging generally leads to a decrease or cessation of the performance of many vehicle components (for example, air filters).
Once fuel is mixed with water and enters the system, moisture may enter the regulator. Often along with dirt if the filter is faulty.
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To the last drop: how to check the fuel pump yourself?
The death of a fuel pump is always sad. But it's not always obvious. Symptoms of its wear or failure are quite numerous and varied, so it is not always clear whether it is to blame for the abnormal behavior of the machine or not. Moreover, some of its malfunctions lead to symptoms that are characteristic of leaking injectors, misfires, low compression, and much more. Therefore, diagnosing a fuel pump is not only entertaining, but also often necessary. Especially if nothing else helps.
Very briefly about the symptoms
Fortunately, most engine problems can now be diagnosed using a scanner. This makes life much easier for motorists and car service workers, if only for the reason that misfires or sensor malfunctions do not need to be looked for using complex conclusions and step-by-step replacement of everything. There are exceptions, of course, and no one excludes working with the brain, but still. But what to do if all the electronic systems are in order, there are no errors, but the car is desperately stupid? This is where they usually remember that there is such a part - a fuel pump. And you have to check it the old fashioned way - with your hands, and not with a laptop.
I will not describe in detail the symptoms of the breakdown: a lot has already been said about this. In short: failures, decreased dynamics, inability to start the engine, sometimes the engine tries to stall when turning, squeals and squeaks in the area of the same fuel pump. This could be the end of the symptoms, but the fuel pump has another malfunction: the valve that holds the pressure in the rail may stop working. In this case, the symptoms of the malfunction are very similar to those that are often tried to be attributed to a leaking injector: the engine does not start immediately, you have to turn the starter for quite a long time. This rarely happens, but we’ll still talk a little about this situation below. Now let's move on directly to the diagnosis. So, the engine does not start, there are no ignition errors. Where do we start?
Mindfulness itself
No matter how complex the car may be, there can be only two breakdowns that prevent the engine from starting: no gasoline and no spark. If there is a spark, you need to look for at what stage the gasoline disappears. And first you can make sure that it is definitely not there.
If access to the candles is easy, then the most basic action will be to unscrew these same candles. If they are dry, something is wrong with the fuel supply. So, we are going in the right direction.
When you turn on the ignition, we listen carefully: after turning on the ignition and before turning on the starter, you can usually hear a characteristic “zh-zh-zh” in the rear for a couple of seconds. It is the pump in the gas tank that turns on. If this “w-w-w” has always been heard, but now it’s not, it means the pump is not turning on. We think why.
First, we check two basic things: the alarm and the fuse. Most anti-theft systems provide for turning off the fuel pump. Therefore, you need to make sure that the alarm, immobilizer and everything else that was once installed on the car worked. If all this wonderful electronics is working properly, we check the fuse (we open the fuse diagram, look for the right one and make sure that it is intact). You can also check the relay, but it’s difficult to do without a multimeter. Therefore, you can skip this stage for now: the relay is usually intact anyway, and the reason is somewhere further.
Diagnostics and troubleshooting of check valve operation
So, you suspect that the vehicle's performance has decreased due to a malfunction of the fuel system check valve, and there are some signs of its malfunction. In order to find out whether this is so, several methods are used.
Most often, the pressure level is checked. An adequate pressure level should be about 3 kg/cm2 (for passenger cars). At the same time, the pressure level should not drop sharply when the engine is stopped. Otherwise, this will also be a sign of a faulty check valve.
As mentioned above, hose compression is sometimes used. But this method is not always suitable, since only a rubber elastic hose can be compressed.
Be sure to determine the reason why the fuel system is filling with air. If it is functioning correctly, a small amount of liquid should remain in the chamber awaiting the next engine start. If the valve is missing or worn out, air appears instead of this fluid. Starting the engine in such conditions will be disproportionately difficult.
So, as a result of measuring the pressure with a pressure gauge inserted into the rail, you concluded that after stopping the engine it began to drop significantly. In this case, either there is a defect in the fuel line, or the valve itself is faulty. If the result at the outlet of the fuel pump is different, then the valve is faulty.
To fix the problem, select a high-quality check valve from a spare parts store that fits the cross-sectional dimensions. If you select a valve with the wrong cross-sectional dimensions, it may begin to “slip.” Before purchasing, check the operation of the valve on site, if possible. The check valve must be cut into the line at any suitable location.
For example, this can be done between the fuel pump and the filter. After this, test the functionality of your car by driving it up a hill at an angle. If the car shows no signs of loss of power, then the valve has failed.
Sometimes there is no need to replace the valve, but the fuel pump itself needs to be replaced. However, this procedure is much more expensive. An alternative option is to install an additional valve. When choosing a valve, keep in mind that models for Russian cars often differ in cross-section from foreign cars.
There is also a folk method for troubleshooting, but it is only suitable if the valve is clogged. You need to hit the valve a couple of times with a hammer. The impact force must be calculated to avoid mechanical damage. With this effect, foreign bodies trapped in the valve can be crushed or even fly out of the valve. But most often it is much easier to replace the valve with a new one.
conclusions
The fuel system check valve is an important component of this system, the failure of which can cause a lot of problems for the driver. This will be especially painful during movement. Therefore, it is worth using only high-quality fuel, and at the slightest sign of a malfunction, which were listed above, diagnosing the fuel system.
After all, the problem may lie not only in the valve, but also in other small parts. Diagnostics at a service station almost always reveals such faults, so do not forget about timely maintenance of the car, even if everything seems to be in good order. Good luck and easy travels!
Which way to go
There are two options for eliminating the problem. Take the car to a service station and wait for the repairs to be completed. In this case, you need to shell out a certain amount of money, it’s a pity.
Having knowledge and understanding of the car’s structure, you can carry out repairs yourself. Saving money in person. However, there is a possibility of stepping on a pitfall. Can't deal with the problem.
Then you will have to shell out additional money for repairs in a specialized center, how do you like this prospect? In any case, the decision is yours to make.
Experts recommend not to reinvent the wheel, but to give the car to professionals who will replace it quickly, with a guarantee of quality.
Decide what is more important to you: savings or stable operation of the power unit, good luck to everyone!
