What is a fuel injector and how does it work?
A fuel injector is a fuel metering device that sprays atomized droplets of fuel in a specific pattern into the engine’s intake manifold or directly into the combustion chamber. The injector has a solenoid and valve within and the operation, or pulsing, of the solenoid is controlled by the powertrain control module (PCM). The PCM controls the solenoid’s “on” time in order to keep the air-fuel ratio optimized while the engine load and operating conditions constantly change. Fuel injectors are usually connected to a fuel rail located on the top of the engine and the fuel rail, in turn, is supplied with fuel under pressure from the fuel pump located in the fuel tank.
When to consider replacing a fuel injector:
- Rough idle, loss of power, or misfiring. Poor engine operation has many causes but faults in the fuel injection system, including the fuel injectors, are high on the list of possibilities.
- Odor of raw gas or visible leaks. Fuel injectors should not leak fuel into the intake manifold when the car is off. If you notice any fuel odor around your car, the possibility of a leaking fuel injector should be considered. There should be no external leak from a fuel injector. If an externally-leaking injector is suspected, do not start your car due to the fire hazard.
- Check engine light. Some fuel injection failures, for example, a faulty solenoid, may cause a trouble code to be set in the PCM and that will cause the check engine light to illuminate. The codes are read and the fuel injector is tested directly, as needed.
- Major engine repairs, engine replacement, or lengthy storage. All fuel injectors will have deposits given enough mileage. These deposits can cause an imbalance in the performance of the injectors from cylinder to cylinder. When an engine is already disassembled, or if you are installing a new engine, that is a perfect time to service the injectors as a set. All injectors have tiny internal filter baskets. A professional injector service facility will clean each injector ultrasonically and replace these filters for a relatively low cost.
How do mechanics replace a fuel injector?
Injectors can be serviced once removed from the car or replaced outright with new injectors. If the injectors are serviced, specialized cleaning and test equipment are required. The choice to repair versus replace will depend on exactly what is wrong with the injector as well as customer preference. Either option requires removing the injector from the car and the following procedure is typical:
- Once the engine is cold, the pressure within the fuel rail is relieved by briefly running the engine with the fuel pump fuse out.
- The upper plenum on the intake manifold is removed along with any cables, hoses, or wiring that restricts access.
- The supply and return lines are removed from the fuel rail. The electrical connectors to each fuel injector are unlocked and removed. The fuel rail is then unbolted and removed from the intake manifold.
- The injector(s) requiring replacement are removed from the fuel rail, taking care to not allow any debris to enter the exposed openings. An O-ring seal usually holds the injector very firmly in a finely polished bore in the fuel rail.
- Using a new O-ring, the serviced or replaced injector is re-inserted into the fuel rail — using engine oil on the O-ring to prevent damaging it. O-rings in this application fit very tight to prevent fuel leaks.
- The fuel rail is re-installed and the supply and return lines are re-connected. The plenum is re-installed along with all cables, hoses, or wiring.
- Finally, the engine is run, there is a careful check for leaks, and the vehicle is road tested.
Is it safe to drive with a fuel injector problem?
Yes, so long as there is no external leak of fuel from a broken or malfunctioning injector, it is safe to drive the car. However, if the injector is known to be malfunctioning, it can cause engine misfires, excessive emissions or, in the case of a badly leaking injector, can overload and overheat the catalytic converter. Additionally, fuel efficiency will always be diminished if the fuel injectors are not working properly.
When replacing a fuel injector keep in mind:
- Using high quality (Tier One) gasoline may reduce deposits on fuel injectors and prolong their life.
- If an injector problem develops that requires removal of one injector, the best practice is to remove and service all of the injectors at the same time. That service might involve replacement of the electrically failed injector along with off-the-car cleaning of the remaining injectors. Serving all injectors at once ensures the injector set will be balanced, in terms of flow rates, and in turn promote smooth operation of the engine.
- Do not use fuel system cleaning compounds, or procedures, unless such materials are specified by the manufacturer of your car.
- On the car cleaning of fuel injectors is not as effective as off-the-car cleaning because injectors have tiny internal filter baskets that should be replaced as part of the process of servicing a fuel injector.