By: Don Bowman Bad fuel injector symptoms are important to spot before they create a big problem for your engine. Fuel injectors are an electro-magnetic device used to dispense metered fuel into the engine. The injector has a nozzle with holes similar to that of a hypodermic needle, which can easily become clogged. Injectors can go from one extreme to another with a certain amount of middle ground. An injector that is worn out, not functioning at all or clogged with dirt has the same end result: it lacks power and produces an engine misfire. When a fuel injector screen becomes clogged or the orifices carbon over, the fuel discharge becomes extremely erratic, which will result in an uneven idle, a misfire at mid range and an out-of-range fuel trim. The computer, through signals from the oxygen sensor, will recognize this and will illuminate the check engine light. The worse case scenario is a fuel injector that has failed in the open position. This will immediately flood the cylinder with fuel, disabling the spark plug and allowing raw fuel to flow into the exhaust system. This can be a dangerous situation since, in severe cases, raw fuel may pour out of the exhaust with the engine running. It will also destroy the catalytic converter in short order. In a less severe situation, the fuel economy will take a dive. Another problem common with fuel injectors is a leaking injector body or a leak at the o-ring on the top inlet port on the injector where it plugs into the fuel rail. This can be seen with the engine running and a strong smell of gas will be present. A broken lower o-ring will cause an air vacuum leak at the manifold. Depending on the severity of the leak, a misfire will occur and a conflict with the computer with respect to the fuel mixture which is now unmanageable within the correct parameters.