While almost all new vehicles on the road today are fuel injected, most drivers wouldn’t know that the concept of fuel injection has been around for close to a century. Manufacturability, cost, and complexity prevented fuel injection from becoming mainstream at that time, however as technology improved, fuel injection became widespread in the 1980’s with the advent of the modern engine control unit (ECU). Even today, fuel injection continues to evolve in the form of direct injection to achieve ever higher miles per gallon. However, as with all technology, maintenance becomes more and more of a focal point as complexity increases. As such, it’s not uncommon to have to replace a faulty fuel injector on a modern fuel system from time to time.
Function of a Fuel Injector
A fuel injector provides a way to spray atomized fuel (imagine a mist of fuel with extremely tiny droplets) into the combustion chambers of a car’s engine. Pressurized fuel is supplied to the fuel injectors by the fuel pump and is distributed to each individual injector via the fuel rail. This high-pressure fuel is dispersed into an atomized spray via a nozzle which allows the fuel to efficiently mix with air. This mixture is highly combustible and is ignited by the spark plug, which causes the mixture to explode. This process is repeated continuously in each cylinder which keeps your engine running.
Common Symptoms of a Bad Fuel Injector
The fuel injector is meant to spray atomized fuel for ignition inside an engine. Because of how precise the fuel injector’s atomized spray is, even small fluctuations from a faulty fuel injector can cause big problems for your engine’s ability to run smoothly and fuel efficiently. The following is a list of common symptoms associated with a faulty fuel injector.
Poor Fuel Economy – When a fuel injector is stuck open, it more or less dumps unregulated amounts of fuel into your engine. One place you can feel this is in your pocketbook, as the additional fuel burn will deplete your tank faster and cause more frequent trips to the gas station. Fuel injectors can become stuck open for a number of reasons, but faulty electronics or clogging due to debris in your fuel system that slips through your fuel filter are two of the most common causes.
Poor Running – When a fuel injector sends an incorrect amount of fuel to the engine, running issues are typically the result. Whether it is stuck open, stuck closed, or metering fuel inconsistently, your engine is getting more or less fuel than your car’s ECU thinks which means that your car likely won’t run right. You may notice starting issues, poor idle, an increase in emissions during a smog check, or hesitation and stumbling during acceleration. Depending on the root cause of the problem with the fuel injector, these symptoms can be constant or intermittent.
Replacing a Fuel Injector
Replacing a fuel injector may seem like a complicated task, but with a few simple tools you can take out one or all of them pretty quickly and easily. When dealing with anything fuel related, safety must be a priority. Always wear protective clothing and protective eyewear. Additionally, make sure you work in a well ventilated space where fuel vapors can disperse to avoid creating a fire hazard. Finally, avoid sources of ignition such as electricity and smoking when working with your fuel system to limit fire risk.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – You need to release the pressure from the fuel system before taking anything apart. The easiest way to release any pressure in your system, whether you’ve recently run the vehicle or not, is to run the vehicle until the fuel is removed from the lines. To accomplish this, you want to find either the fuse that controls the fuel pump or the relay that supplies power to the fuel pump. You will want to disconnect one of these to stop power to the fuel pump (which creates the pressure in your fuel system). You can then start your car and let the engine run until it dies, which is your indication that your fuel system is clear of fuel and residual fuel pressure has been dissipated. Do not remove any components prior to completing this step, otherwise high-pressure fuel can spray and cause potential injury.
It should be noted that some fuel systems, such as direct injection systems, run significantly higher fuel pressure than average (sometimes in excess of 2000 psi). This highly pressurized fluid can cause significant physical harm if you do not depressurize safely and properly. If you have a high pressure fuel system, consult a factory service manual to make sure you have a complete understanding of the risks and how to mitigate them safely.
Step 2 – Once the fuel pressure is completely released, you can work to disconnect the fuel rail that connects to the fuel injectors. Based on your vehicle, that may involve removing your intake manifold, intake hose, air filter, or any other components that are in your way. This step differs for every vehicle as it is highly dependent on engine bay geometry (which is very different vehicle to vehicle). Once everything is removed, the fuel rail is most likely held with screws or bolts to the intake manifold. You need to remove those fasteners (most often using a ratchet and deep sockets) and remove the fuel rail carefully, being careful to contain any residual fuel that may spill.
Step 3 – Each injector will have a wire harness attached to it, either on the top or the side. It may require removal of a clip or require that you bend tabs out of the way with your fingers before you can remove the connector. It is important to be gentle, as the connectors are often plastic, which can become brittle and prone to cracking due to the repeated heat cycling of the engine over time. Be careful not to damage a connector.
Step 4 – After removing the connector, next you will need to remove the injector from the manifold. There are special fuel injector pliers that grip the injector firmly and remove it without damage. You don’t necessarily need specialized pliers to remove the injector if you are careful. The injector essentially just slides out.
Once the injector is out, you will have a hole in the intake manifold until you install an injector back into the manifold. Be sure to cover the hole and prevent any debris from entering into the manifold or engine if you aren’t replacing the injector immediately. Reinstallation can be completed by following the removal steps in reverse.
Best Fuel Injector Brands
There are aftermarket and OEM fuel injectors available for most vehicles, but it can be hard sometimes to choose the best fuel injector brand for your car. While there are many brands to choose from, we have had great luck over the years with our favorites, which are listed below.
Bostech specializes in fuel injector technology and service. They offer full rebuild kits for most fuel injectors on the market and are the leader in rebuilding services for a wide variety of fuel injectors from diesel or gas engines. Bostech also wells new fuel injectors as well. Whether you want to service your injectors yourself or just swap new ones in without the hassle, Bostech injectors are a reasonably priced, high quality way to go.
Bosch is a large global manufacturer that offers OEM and replacement fuel injectors for pretty much every auto brand in the world. They continually drive innovation through motorsports and are always working on future technological developments in fuel delivery and management. They are used almost exclusively (with the exception of VDO) by many German car manufacturers and are widely regarded as being of very high quality.
VDO is one of five brands under the Continental brand of companies that develops technologies for auto manufacturers and the aftermarket. They also support motorsports heavily and use that research to produce high level quality and durability for their products. The make a wide range of electromechanical products ranging from instrument cluster gauges to fuel injectors. Speaking of their injectors, they are of great quality while remaining affordable. Overall, it’s hard to go wrong with a set of VDO fuel injectors.