Fuel injection components are very costly and replacing these parts without investigating the problem thoroughly will be an expensive exercise. If you experience a problem with your fuel supply, bring your car to us, where it will be tested by experienced technicians on the correct equipment.
An engine will not perform at its best without the proper air/fuel mixture. The fuel mixture of a modern computer controlled fuel injection adjusts the fuel/air ratio very accurately, but it can develop problems with:

The air mass meter measuring the incoming air
The lambda oxygen sensor measuring the exhaust oxygen content. The throttle body adjusting the air-flow into the engine The petrol or diesel injectors measuring the exact quantity of fuel required by the engine. Precise ignition timing and spark.