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Why your injector always fail?
Time:2018-10-29
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The common rail injector is the most sophisticated component in the electric diesel engine. It is used to spray fuel with pressure 160 mpa into the cylinder for combustion.
 
The fuel injector requires very strict cleanliness fuel and can be damaged by water or impurities above 5 microns.Today,we are going to take apart an common rail injector that's worn out and show you the details.
common rail injector
 
This is an electric fuel injector from Bosch, Germany. At present, most of the fuel system in the electric diesel engine in China uses it.It's not cheap.Each one cost more than one thousand RMB.For a six - cylinder engine, you will spend more than 10,000RMB if you replace all of them.
injector
 
First remove the solenoid valve at the top of the injector whose function is to  is to control fuel injection.It allow the fuel to be injected into the cylinder at the correct flow at the correct time.
common rail valve
 
Here is the control valve,consist of cap and valve rod,is one of the most easily worn parts in injector.
 
There are two control valve rod in the plate.For comparion,left is worn one while right is brand new in BASCOLIN brand.
 
Enlarge the picture and we see that lefe is severely worn, which is almost fatal for the injector.
 
 
Needle valve worn
 
Let's take a look at the control valve cap again. Its dent is also one of the most easily worn part.There is a steel ball in the dent which solenoid valve controls fuel injection through it.When the inner part of the dent is worn, the return oil of the injector will be increased due to loose closing of the steel ball, resulting in loose closing of the needle valve.
 
These pits are so small that I used a Canon hundred micrometres lens to capture the details.Even so, it's hard to see clearly.Then we could know how precisely the parts in the injector are processed.
 
This part is the common rail nozzle of the injector.Its function is to inject the fuel from its head into the cylinder.In the whole injector,its working environment is the worst.Because it Because it must work in the high temperature cylinder.
 
The nozzle needle valve tip acts the function of sealing oil.When there is no need to spray oil, sealing job must be done without leakage.It can be clearly seen from the photo that the tip of the nozzle needle valve has been severely worn, which may cause the injector to drip oil when working.The injector oil drip can cause the piston to overheat locally and even cause the piston to perforate.
 
Finally, let's look at the orifice of the common rail nozzle.They are used to inject fuel into the cylinder.Its diameter is so small that it is barely visible to the naked eye.While the amount of injection per unit time depend on the diameter of the hole directly.If the fuel contains particle impurities, it will cause irreparable wear to the orifice hole.As time passes, the diameter of the orifice hole will become larger.It might cause the increased oil supply,resulting in torque exceeding the limit, black smoke, high fuel consumption.
 
Clearly, the nozzle orifice hole on the left is much larger than the new nozzle in BASCOLIN brand on the right.It means the nozzle on the left has been worn badly and cannot be used anymore.
 
Maintenance and repair of Common Rail injector 
The fuel injector shall be checked and adjusted once after working 700 hours.If the opening pressure is lower than the specified value of 1 Mpa or the needle valve head carbon accumulation is serious, the needle valve should be unloaded and put into clean diesel to be scraped carbon accumulation with wood chips.The injection hole is dredged with fine steel wire and adjusted after loading. It is required that the pressure difference of each cylinder of the same machine must be less than 1 Mpa.Then the oil seal test was conducted, that is, the injection pressure reached 18 Mpa and let it drop to 17 Mpa by itself. When the oil recovery time is not less than 10 s square,then it is qualified.During the test, the diesel oil is not allowed to flow down from the cone and the injector head is not allowed wet.In addition, the injected oil must be mist and crisp banging sound, porous fuel injector holes should also be a cluster of fog.
 
In order to make the diesel fuel injected into the cylinder of the injector can be fully burned in time, the oil supply time of the pump must be checked regularly.If the oil supply time is too early, the vehicle will be difficult to start and the fault of cylinder knocking. If it is too late, black smoke will appear in the exhaust.
 
Because of high precision combination of the needle valve in the injector, and the small orifice size,so the clean diesel must be selected according to the seasonal change strictly, otherwise the injector cannot work normally.When refueling, do not mix into rain or snow water, avoid refueling in dusty environment.We need to maintain diesel filter on time, often discharge filter and oil in the tank precipitation in order to prevent the invasion of ash and sand impurities and aggravate needle valve wear.
 
When cleaning needle valve,do not collide with other hard objects, nor make it fall to the ground to avoid bruising.Before replace the needle valve couple, we should first put the new needle valve into 80 ℃ diesel oil to be heated for 10s.When rust-proof oil is fully melted, and then put in a clean diesel to twitch back and forth  in the valve body, wash thoroughly.In this way, it can avoid the failure of sticking needle valve due to the melting of anti-rust oil when the injector works.Needle valves must be replaced in pairs and not interchangeable.
 
If a large number of bubbles or oil bubbles appear when releasing the high-pressure pipe connection,it means the needle valve is stuck in the open state.Therefore, the compressed gas produced by cylinder compression will flow back to the high-pressure tubing through the injector.At this moment,you could touch the high-pressure oil pipe by hand. If the pulse is not felt or weak, it means the needle valve is stuck.
 
Tips to the maintenance of common rail injector
When the fuel injector in need of repair is hard to be removed due to the binding on the cylinder cover, we could decompress the diesel engine and rotate the crankshaft.When the speed is raised, put down the pressure lever immediately and use the cylinder pressure to get the injector out.But note that no person around.We can also check the fuel injector on the car.A tee coupling can be used to connect the fuel injector to be checked with the standard fuel injector to the fuel pump.At the same time, remove the other cylinder high-pressure pipe,roll the crankshaft or use the starter band to transmit the motor,check the injection situation.If two injectors inject oil at the same time,it means the injection pressure is normal.If the injector to be checked is found to inject earlier,we can know that  the injection pressure is too low.Otherwises too high.The diesel engine cannot be idled for a long time to prevent the diesel atomization,result in deterioration of the fuel injector.And the vehicle cannot be overloaded for long time, in case the overheat body causes the injector needle valve to get stuck.For a long time storage engine, the fuel injector shall be removed and soaked in clean diesel oil before installation to prevent the needle valve from rust and cannot be used.
 
In short,you need follow strict implementation of the maintenance standards to extend the life of the injector.