Fuel injectors are designed to last as long as the engine itself. However, multiple factors as carbon buildup, design flaws, overheating, and many others may decrease its lifespan.
The goal of this article is offering you a detailed guide on how to replace fuel injectors. Although the procedure is not specific to any particular brand or model, it is written so that it can be used as a reference during this important work.
What tools do I need?
Depending on your fuel injection system (MPI, TBI, GDI) you may need the following items at hand:
In addition to the aforementioned tools, you may also need:
Fuel injectors o-ring seals
Intake manifold gasket and/or seals (depending on your vehicle this may not be necessary).
Flat/Slotted screwdrivers, try having short and long reach types (from 1” to 10”)
Phillips screwdrivers, similar to before try having short and long screwdrivers for difficult to reach areas
Assorted Torx screwdrivers and keys, usually from T10 to T25
Metric Allen keys sets
Ratchet and socket set. Most vehicles require both 3/8” and 1/2" drive sets to work with bolts ranging from 8mm to 30mm.
A set of metric combination wrenches (6mm to 19mm) is highly advisable
Depending on your vehicle make-model-year, you may need a standard flare nut wrench set (? to ?) to disconnect the fuel lines
Assorted pliers of different sizes
A fuel pressure gauge equipped with a pressure relief valve
Safety goggles and appropriate gloves.
Safety always comes first
Replacing injectors involves working with your vehicle fuel delivery system, that’s why we suggest extreme caution. Please follow all safety precautions recommended by Occupational safety and health (OSH) guidelines:
Do not smoke. Gas vapors, not liquid gasoline, is which burns. For the same reason avoid flames, sparks or other sources of ignition near the vehicle while you are working.
Work on an area with proper ventilation. Avoid closed garages, basements, etc.
Avoid breathing gas vapors or mists.
Avoid skin, face, or eye contact with fuel, wash thoroughly with soap and water in case of contact.
Use shop towels to clean up possible spills to avoid them from spreading.
Disconnect the negative terminal of the battery, and turn off any possible ignition source.
Always relieve the pressure from the fuel delivery system prior to starting working on any of its components. Remember these are high-pressure systems, using safety goggles and gloves is highly advised. See step 7 of “Fuel injectors replacement procedure” for detailed instructions on how to do it in a safe manner.
Fuel injectors replacement procedure
The following procedure will assist you to replace fuel injectors on most Multiport Injection (MPI), Throttle Body Injection (TBI), and some Gasoline Direct Injection (GDI) equipped vehicles.
IMPORTANT: follow all instructions from the previous section BEFORE continuing.
1. Wait until the engine is completely cold
Our advice is waiting at least 8 hours to let the engine cool down, especially aluminum parts. If you can wait from one day to another even better. Remember that you may have to put your hands in narrow places and thus you can get burned.
2. Remove the engine plastic cover
Using the screwdrivers or ratchet and sockets remove the protective plastic cover (if any). Double-check the engine is completely cold before continuing.
3. Disconnect vehicle battery
If you didn’t already do so, disconnect the negative terminal of the battery using the appropriate open-ended wrench.
4. Locate fuel injectors
TBI - Throttle Body Injector
MPI - Multi Port Injector
GDI - Gasoline Direct Injector
On TBI vehicles you will need to remove the air filter to gain access to them. This type will be mounted on the throttle body. On MPI vehicles with L4 and L6 engines, you will see the fuel rail holding the injectors on the lower section of the intake manifold. On MPI vehicles with V6, V8, and V12 engines you may not be able to locate injectors since they are usually under the intake manifold.
5. Evaluate the situation
Once you locate fuel injectors take a moment to plan ahead. TBI systems and MPI systems with in-line engines are easier to work with. Most of the time they only require removing the fuel rail and fuel lines to gain access to injectors. V-engines, on the other hand, requires removing the intake manifold. Depending on engine design, you will need to remove/loosen accessories, covers, fuel lines, vacuum lines, A/C lines, sensors, wiring harnesses, and more.
PRO TIP: don’t skip this step. Double-check you have everything required to remove the injectors. Some engines demand the use of long Torx bits, Allen bits, even security Torx bits. Save yourself of unnecessary hassle, you may lose gaskets and seals if you discover half-way that you can’t complete the work.
6. Take pictures before starting
If this is your first time removing fuel injectors, or you don’t have the vehicle repair manual at hand then we suggest you taking as many pictures as possible. Don’t hesitate to stop and take pictures each time you consider it necessary.
PRO TIP: Depending on the vehicle you may end up with dozens of bolts of different sizes and lots of disconnected accessories. Classifying bolts and/or taking pictures may look like a waste of time until you need to reassemble everything.
7. Relieve fuel system pressure
As mentioned in the previous section “Safety always comes first”, fuel system pressure should be released to avoid unnecessary risks. Most modern vehicles have a fuel pump test point, which is usually near the fuel injectors. The safest way to relieve fuel system pressure is by using that test port:
Ensure the ignition switch is in OFF position
Open the gas cap so allow fuel tank pressure to be relieved
Attach the fuel pressure gauge to the fuel pump test fitting (usually a Schrader valve)
Turn the ignition switch to ON position (don’t start the engine)
Wait until the fuel pressure stabilizes, you can tell by looking fuel tester needle stop
Now slowly open the fuel pressure relief valve on the fuel gauge. Remember to collect excess fuel to an appropriate reservoir
Wait until the gauge indicates the system is totally depressurized
8. Gain access to fuel injectors
Use adequate pliers to disconnect accessories, sensors and other electrical harnesses connectors.
Use screwdrivers, and appropriate sockets/wrenches to remove plates, brackets, accessories, vacuum lines, and sensors. Sometimes instead of removing the components, loosen them is enough to gain access to fuel injectors. Proceed as necessary.
Carefully remove the intake manifold (if necessary)
PRO TIP: It’s a good practice to cover the intake manifold inlets with a cloth to prevent any tool/bit/dirt from accidentally falling inside the engine
9. Remove fuel rail and injectors
Use adequate pliers to disconnect fuel injectors electrical connectors
Use the appropriate wrench/socket to loosen fuel injector rail
Depending on your vehicle you may need to disconnect the fuel inlet/outlet line from the fuel rail
Carefully lift the fuel rail along with fuel injectors. You will need to pull it up using the right amount of force.
PRO TIP: professionals have a trick for this step. You will need two long flathead screwdrivers. Rest the tip of a screwdriver on the intake manifold parallel to the injector rail. Holding the first screwdriver firmly, put the second one perpendicular to it below the injector rail (making an “X”). Now carefully pry using the first screwdriver as a support so that you can press up on the injector rail using the second screwdriver. The goal is to push the rail up in a controlled manner, being careful not to deform the injector rail. Repeat this procedure by pushing up on both ends and in the center of the injector rail.
10. Remove old fuel injectors from the rail
Using adequate plier/screwdriver remove the fuel injector bracket/clip
Pull each injector with extreme caution to avoid damaging it. This step is tricky since the o-ring seal will play against you. Have patience, using a flat screwdriver is sometimes useful to pry injectors from the rail.
Clean up fuel drips and cover intake manifold to prevent dirt from entering the engine.
10. Install new fuel injectors in the rail
Compare old and new fuel injectors. Double-check part numbers before proceeding to their installation.
Whatever possible, it’s the best practice to test new fuel injectors on a fuel injector test bench prior to installation. That ensures they are working as expected. When you buy your injector from us, they will already be tested and ready to install.
Lubricate fuel injectors o-ring seals with grease or engine oil to facilitate installation.
Install each injector on the fuel rail. Push firmly until it stops. Turn left and right each injector once installed to double-check that its o-ring is fully seated.
Reinstall fuel injectors clips and/or brackets if necessary.
11. Reinstall fuel injector rail
Line up injectors with their respective holes and firmly press down until the o-rings are fully seated in the intake manifold.
Use the flashlight to triple-check all injectors are at the same height/deep within the intake manifold.
Tighten injector rail bolts. Do it evenly so ensure all injectors are fully seated.
Reconnect fuel line (if necessary).
Reconnect fuel injectors electrical connectors.
PRO TIP: due to the amount of work involved, professionals always check for fuel leaks before reinstalling the intake manifold. Connect again the fuel pressure gauge. Momentarily, reconnect the battery and turn ignition key to ON position (engine off). Wait for 10 seconds and turn ignition key OFF and then ON again (engine off). Repeat this a couple of times until the fuel gauge reads the pressure on the rail. Use the flashlight to check for leaks. If you notice any drip between the fuel injector and the rail or in the fuel line then correct it before continuing.
12. Reinstall intake manifold and other components
Replace intake manifold gasket as required
Using the appropriate tools reinstall the intake manifold. Tighten it evenly to avoid vacuum leaks afterward
Reinstall all accessories, brackets, plates, vacuum lines, wiring harnesses, and components. Those pictures you took previously come handy now.
13. Check for fuel and vacuum leaks
Reconnect the battery
If you didn’t already, pressurize the fuel system using the pro tip of step 11.
Start the engine. It will be OK if it takes longer than usual since some air could be present in the system.
Wait until the idle stabilizes and then use the flashlight to perform a thoughtful inspection for fuel leaks.
If the idle doesn’t stabilize it could be an indication of vacuum leaks. Double-check that you didn’t miss to reconnect MAF or MAP sensor before removing the intake manifold.
14. Clean up and erase any DTC stored in memory
If everything goes as expected then clean up the engine and reinstall its plastic cover
Erase any Data Trouble Code (DTC) that may have been stored in memory.
DIY or hire a professional?
As you can see, replacing fuel injectors is not difficult, but doing it the right way requires a lot of patience, manual skills, and caution. As mentioned at the beginning of the article, some vehicles are easier to work with than others. In-line engines with MPI injection are usually straight forward. However, if you own a next-gen GDI vehicle with DOHC V-engine then paying $400 for labor might be your best course of action.