Modern cars don't have a carburetor responsible for delivering gas to the engine. Instead, they have electronically controlled fuel injectors, which deposit a metered amount of fuel to each cylinder via the intake manifold. Like any automotive part, they can wear out or become damaged and require replacement. This article deals with how to tell if an injector needs replacement.

Testing fuel injectors

A failed injector can result in poor engine performance (insufficient power, missed engine firings, or even engine damage). Likewise, an injector that works, but leaks fuel can also cause the engine to operate poorly (reduced power and increased emissions marked by black smoke in the exhaust). To check whether the injectors are opening and closing, you or your mechanic may use a stethoscope placed against each one. If a clicking sound is heard, it indicates that the injector is operating. If there is no clicking sound, the injector is not working. Before having it replaced, the operation of the injector solenoid, the wiring harness and the control module circuit should also be checked. A "noid light" can be used to test the fuel injector feed circuits. There are different versions of noid lights that are made to fit the wiring harnesses of different car manufacturers, and a good mechanic is likely to have sets that cover most models. What a noid light can determine is whether or not an injector is receiving power from the control module. The injector balance test is another way to ascertain if the injector is faulty and needs replacement. An electronic fuel injector tester is used to force an injector to run for a controlled amount of time. A pressure gauge is attached to the fuel rail test fitting and the tester is activated. The process should be repeated for each injector so that the results can be compared across them all. If the gauge is showing a pressure drop coinciding with one injector that is less than the drop shown with the other injectors, it is a sign that the injector may be clogged or needs replacement. Similarly, if one injector shows a pressure drop that is higher than the others, the injector may be worn or sticking, and in need of replacement. To test whether an injector is clogged or needs replacement, a mechanic may use a fuel injector cleaning tool--if the engine's performance improves after the injectors have been cleaned, that was probably the solution to the problem. A fuel injector must operate properly millions of times over its lifetime, but modern manufacturing practices are such that an injector failure is rare. Although it is one of the more critical parts of the fuel system, luckily it is easy to replace, and can be done without the need for special tools.

Source:

Modern Automotive Technology; James E. Duffy; 1998

Resource:

Fuel injector replacement