Proper maintenance of the fuel system is crucial for consistent long-term performance of a vehicle. The most easily clogged parts of the fuel system are the fuel injectors themselves. There are a number of ways this can happen:
Whenever an internal-combustion engine is powered down, the combustion chambers have leftover fuel/exhaust hanging around. While the engine cools, the vaporized gasses settle on every surface in the combustion chamber, including the fuel injector nozzle. Over time, this residue can reduce how much fuel the injector can deliver to the engine. There is not much to do to prevent this, but if the engine has worked particularly hard (lots of uphills or high temperature) it may be a good idea to let it cool down a little before shutting the engine off. Driving more gently towards the end of a trip can extend the life of the fuel injectors.
Heat in the cooling cylinders can also cook residue and other impurities onto the injectors, making cleaning significantly more difficult and time-consuming.
Fuel injectors can get clogged up by debris. This can either come from gas or from the fuel system itself. Gasoline with impurities in it is less common these days, and most major gas stations have consistently high-quality gas. Still, debris can get into the tank and, consequently, into the fuel system. The fuel filter catches the majority of impurities but a small amount could make it past.
If there is any water in the fuel, corrosion can happen within the lines and fittings of the fuel system. This corrosion can make debris that gets jammed in the injectors.
How to clean the fuel system
For residue in the fuel tank, the tank can be removed and flushed out. This is a very labor-intensive service, and does not need to be performed as part of regular maintenance.
The fuel pump is difficult to access as it is generally mounted inside of the gas tank. If there is a problem causing the fuel pump to malfunction, it will usually be replaced.
Fuel lines can be flushed out if there is debris causing problems, but soft fuel hoses should be replaced if they are showing their age.
Fuel injectors can be flushed to remove debris, but in order to remove baked-on residue from soaking and other tough problems, a full cleaning should be done to the injectors. This means removing the injectors and cleaning (then testing) each one.
A clean fuel system will deliver fuel more consistently and provide the owner with more reliability and higher efficiency.