It's easy.Remove the injector and test it in the test bench.There are many such machines,like CRS-3000.Different companys have its related code for that.Here are some conditions you need to replace your injector:

1.1 The detected injection pressure does not reach the corresponding technical standard

1.2 The poor atomization

1.3 Oil drip or leakage

 

2.1 We can judge the quality of diesel common rail injector by starting difficulty of the engine cooler or the exhaust smoke after starting

2.2 In the basis of oil supply angle and cylinder pressure are standard,if it's difficult to start,exhaust black or white smoke after starting,there is high possibility of failure in injector and high-pressure pump.

2.3 We can judge every single cylinder injector performance.

After the engine starts, maintain a stable speed, and then loosen the high-pressure tubing one by one, which is to disconnect the oil supply of a cylinder to see if the speed of the engine changes.If the generator speed decreases significantly,it means the combustion of this cylinder is effective for the engine.We can identify that its injector is in good condition.Otherwise the injector is broken.

2.4 If we remove the injector and see carbon accumulation in the nozzle.We can know the injector does not work well.

2.5 If the oil is found to be thinner and the oil has a diesel flavor,it maybe has something to do with the fault of the injector too.

 

Please note that 

1.The service life of injector depends on the maintenance of fuel system somehow.

2.After 1500 hours service time,you need to make an adjustment for injector and common rail pump in test bench.

3.The injector nozzle should be replaced correctly.Internal replacements is not allowed.

4.When you measure the common rail injector,pay attention to the detection of the high pressure pump and fuel pump too.