How to Replace the Fuel Injectors on Cars

by Contributing WriterUpdated June 12, 2017

You can replace the injectors in your 24V Cummins diesel engine yourself. Whether you are replacing your injectors with replacements or upgrading to increase horsepower, you can complete the job in a couple hours. Diesel performance companies offer a wide range of horsepower-increase injectors for a reasonable price. These injectors allow more fuel into the cylinder to increase power. Adding injectors should be combined with a larger exhaust to avoid over-heating the engine.

Under The Hood:

 How to Replace Fuel Injectors in Ford Mustang 3.8

Removal of the Fuel Injectors

Remove the air filter housing and the flexible hose attaching it to the throttle body. Then remove the upper intake by disconnecting the throttle cables and any coolant or vacuum lines. This will give you access to all the upper manifold bolts. Pull out the upper manifold bolts and upper manifold, and set them out of the way.

Disconnect the fuel lines and electrical connectors. Do this by first inserting the fuel line disconnect tools into the ends of the connectors to release the connectors; twist while pulling to slip the end of the fuel lines from the injector rail. Then unplug the injector electrical connectors by removing the retaining clips and pulling the connector from the injectors.

Unbolt the injector fuel rails from the lower manifold, and pry up on the rail to release the rail and injectors. Once the bolts on the rail are removed, the only thing holding the injectors in the manifold are rubber O-ring seals that may have become stuck over time. Make sure to remove the old seals if they stick to the manifold, as the new injectors are supplied with new seals.

Remove the injectors from the rail by removing the retaining clips and twisting while pulling until they pop loose. Be sure to keep the retainers as new ones are not usually supplied with the injectors.


Install the new injectors in the fuel rail by applying a small amount of silicon-based grease, and twisting while pushing in. Then reinstall the retaining clips, and rotate the electrical connector into their proper orientation on the rail.

To put the fuel injectors into the manifold, apply a small amount of silicon grease to the rubber O-ring seals and position the injectors into their openings in the manifold. Then press down to push the injectors into place inside the openings, and reinstall the fuel rail bolts. Next, plug the fuel lines in until you feel them snap into place, and then plug in all the injector electrical connectors.

Remove the old upper to lower manifold gasket, and position a new one on the lower manifold. Then sit the upper manifold carefully into place and start all the bolts. Tighten in a pattern beginning in the middle and working outward to the ends of the manifold.

Reinstall any vacuum lines and coolant hoses, and top off the coolant. Then return the air filter housing and flexible hose.

Prime the injectors by turning the ignition key off and then on again three or four times; then start the engine. Check for any fuel or coolant leaks, and test drive the vehicle if no problems are found.

Items you will need

  • 1/4 inch drive socket set

  • 3/8 inch drive socket set

  • Screwdrivers

  • Pliers

  • Metric wrench set

  • Fuel line disconnect tools

 How to Replace Fuel Injectors in a Buick V6


Bring your Buick to a complete stop. Disengage the engine and open the hood. Allow engine to cool. Remove the negative battery cable by loosening the cable clamp with a wrench. Move the cable to the side.

Look at the top of the engine fuel manifold cover and see a round port with the fuel pressure valve in it. It resembles the valve stem you would find on your tires. Attach a fuel pressure gauge. The pressure gauge is equipped with a release valve and an overfill hose. Put the hose into a fuel container and open the release valve to let the fuel out. Close the valve and detach the gauge.

Remove any covers that may be blocking access to the top of the engine. Remove the fasteners with a ratchet and socket.

Loosen the clamps of the air intake pipe on the throttle body. Use a screw to loosen the clamp and pull the hose off.

Disconnect the cables for the cruise control (if equipped) and throttle cable. Use a small pry tool to pop the cables off. Then follow the cables back to the brackets holding them to the upper intake manifold. Remove the bolts retaining the brackets with a ratchet and socket.

Inspect the upper intake manifold and take a note of any hose or electrical cable attached to it. Use some tape and a marker to tag them for identification. Detach the items. Electrical connectors need to be squeezed and pulled to be removed.

Remove the bolts retaining the EGR valve and the MAP sensor valve with a wrench. Pull both valves from the engine.

Tag and number the spark plug wires and then pull them from the spark plugs by pulling on them with your fingers.

Remove the mounting bolts of the upper intake manifold with a ratchet and socket. Pull the manifold from the engine and set it on a workbench. Throw any gaskets into the trash. Stuff shop rags into any opening exposed by the removal of the manifold

Separate the fuel lines attached to the fuel rail manifolds. Use a wrench to loosen the fittings. Wipe up any fuel that may spill. Throw away the o-rings. Tag, label, and disconnect any electrical cables from the fuel rail.

Remove the vacuum hose attached to the fuel pressure regulator. Then remove the retainer bolt with a wrench and remove the regulator.

Loosen and remove the mounting bolts of the fuel rail with a ratchet and socket. Use your hands to pull up on the fuel rail. The rail will come up and the injectors will come out with it. Pull the retainer clip and the injector will come off of the rail. Throw away all o-rings.

Clean the entire area, especially the mating surfaces of the upper intake manifold. Remove all gasket material.


Lubricate the new injector o-rings with some new engine oil and slip them onto the new injectors. Put the new injectors into the fuel rail and slide the clip on.

Push the fuel rail and injector assembly down into the lower intake manifold. Install the mounting bolts and torque them to 84 inch-pounds with a torque wrench.

Attach new o-rings to the rail fuel lines and reconnect them. Tighten the fittings to 13 foot-pounds with a torque wrench.

Position the new upper manifold gasket and lower the manifold down over. Install the mounting bolts and torque them to 19 foot-pounds with a torque wrench. Work your way out from the center when tightening.

Reattach the spark plug wires according to the labeling you did previously. Push the spark plugs on until they seat.

Remount the EGR and MAP sensor valves and tighten the bolts with a wrench. Reconnect any vacuum hoses or electrical connectors you labeled in step 6. Make sure everything is secure.

Reattach the throttle cable and cruise control cable to the throttle body by pushing them on. Reattach the cable mount brackets and bolts with a wrench.

Slide the air intake tube back onto the throttle body and tighten the clamp with a screwdriver. Reinstall any engine covers you may have removed and tighten the bolts with a ratchet and socket.

Reconnect the negative battery cable to the battery and tighten the clamp with a wrench. Engage the engine and check for any leaks.

Items you will need

  • Wrench set

  • Fuel pressure gauge

  • Fuel container

  • Ratchet and socket set

  • Small pry tool

  • New injector o-rings

  • Engine oil

  • New injectors

  • Torque wrench

 How to Replace a Fuel Injector in a Saturn

Removing the Fuel Rail and Fuel Injectors

Relieve the fuel system pressure by removing the fuel cap.

Disconnect the negative cable from the battery with a wrench.

Remove the vacuum hose from the fuel pressure regulator on the fuel rail. Unbolt the two mounting bolts with a socket wrench then remove the regulator.

Disconnect the air intake duct by detaching the connector from the intake air temperature sensor then removing the PCV hose from the duct. Unscrew and remove the hose clamps with a flat head screwdriver at both ends of the duct.

Remove the EVAP canister purge hose and loosen the clamp for the coolant hose from the hose guide. Remove the hose guide and separate the PCV hose from the valve cover. Set aside the hoses.

Unscrew and remove the two nuts from the fuel rail mounting studs with the socket wrench. Remove the engine wiring harness cover from the valve cover and push it aside.

Remove the fuel supply and return lines from the fuel rail by unscrewing the two line fittings with an open-end wrench. Take out the O-rings in the holes and discard them.

Unplug the connectors from the fuel injectors by pulling on their locks.

Unscrew and remove the two fuel rail mounting nuts with the socket wrench.

Pull out the fuel rail/injector assembly.

Free the injector retainers from the small lugs on both sides with a flat head screwdriver. Pull each injector out.

Installing the New Fuel Injectors

Install the new fuel injectors and secure them onto the fuel rail by fastening the retainers back onto the side lugs.

Lubricate the O-rings on each end of the injectors with clean engine oil. Insert the fuel rail/injector assembly back into the intake manifold.

Install the fuel rail mounting nuts and torque them to 89 inch-pounds with a torque wrench.

Reconnect each electrical connector to the fuel injectors. Check to make sure they are securely locked on by slightly wiggling them.

Insert the new O-rings into the fuel line holes. Install the supply and return fuel lines onto the fuel rail and tightly screw on their fittings with the open-end wrench.

Position the engine wiring harness cover onto the valve cover. Tighten the mounting nuts over the studs with the socket wrench.

Follow Steps 4 and 5 in Section 1 to reconnect the EVAP and PCV hoses and the air duct.

Install the fuel pressure regulator onto the fuel rail and tighten its two mounting bolts with the socket wrench. Reattach the vacuum hose to the regulator.

Reconnect the negative cable onto the battery with the wrench. Replace the fuel cap.

Start your Saturn and check for any fuel leaks.

Items you will need

  • Wrench

  • Safety glasses

  • Socket wrench set

  • Open-end (combination) wrench set

  • Flat head screwdriver

  • New rubber O-rings

  • New fuel injectors

  • Clean engine oil

  • Torque wrench

 How to Replace a Fuel Injector in an Elantra

Park the Elantra on a firm, paved surface and set the parking brake.

Pull up the rear seat cushion by grabbing the release strap located between the rear of the cushion and bottom of the seatback. With the seat cushion pulled up, you will see the fuel pump access cover. Use a slotted screwdriver to pry off the cover.

Relieve the fuel system pressure by disconnecting the electrical connector to the fuel pump, which is exposed when you removed the access cover. Pull the connectors apart. Start and run the engine until it dies. The fuel system pressure is now relieved. Open the hood and use a wrench to disconnect the negative battery terminal. It should have a black cover on it. A negative "-" sign is molded into the top of the battery by the terminal. If you have an anti-theft alarm, be sure you know the activation code before you disconnect the battery terminal.

Remove the vacuum hose from the fuel pressure regulator which is located at the end of the fuel rail. The fuel rail is the long metal pipe that runs alongside the valve cover. The top of the fuel injectors fit into the fuel rail. The bottom of the injectors fit into the intake manifold.

Remove the electrical connectors from the fuel injectors by pulling out the wire clip at the bottom of the connector, then pull off the connector. Repeat this for each injector. Move to the end of the injector harness and disconnect the main connector by squeezing the two clips on the sides of the connector and pulling it off of the engine harness. Wrap a piece of masking tape around each injector connector and mark them with a pen so you don't mix them up. Use your fingertip to open the clips that hold the harness onto the engine and slide the injector harness off of the clips. Lift off the harness and set it aside.

Use a wrench to remove the two bolts from the diamond-shaped flange that holds the fuel pressure line onto the end of the fuel rail. Directly below the fuel pressure line is the fuel return line. Use a pair of pliers to squeeze the tabs on the end of the hose clamp that holds the rubber hose onto the line. Pull the hose off of the end of the return line.

Use a ratchet and socket to remove the two mounting bolts that hold the fuel rail onto the intake manifold. Grab the fuel rail and wiggle it back and forth to work the injectors loose from the intake manifold. The fuel rail and injectors will come off as a unit. Two fuel rail insulators are exposed when you remove the fuel rail and injectors. If these insulators are cracked or worn, replace them.

Use a pair of needle nose pliers to pull the metal retaining clip off of the injector where it fits into the fuel rail. Repeat this for any injector that you wish to remove. Note that the injector has an O-ring on top of it where it fits into the fuel rail and two O-rings on the bottom where it fits into the intake manifold. Whenever an injector is removed, these O-rings should be replaced.

Apply a thin coat of clean motor oil to the O-rings. Place the O-rings on the injector. Slide the injector into the fitting on the fuel rail and install the retaining clip. Repeat this for any injector you wish to replace. When the fuel rail is fully assembled, mount the fuel rail and injector assembly onto the manifold. Fully seat the injectors into the manifold then install the two fuel rail bolts and torque them to 100 inch-pounds with a torque wrench and socket.

Push the rubber fuel return hose onto the fuel return line. If the hose clamp appears weak, replace it. Mount the fuel pressure line onto the end of the fuel rail. Install and tighten the two bolts. Push the rubber vacuum hose back onto the fuel pressure regulator. Reposition the injector harness and push the connectors onto the injectors. Be sure to snap the retaining clips into place. Reconnect the end of the harness to the main wiring harness. Reconnect the negative battery cable.

Reconnect the fuel pump connector in the passenger compartment. Push the access cover back into place. Replace the seat cushion. Turn the ignition key to the "ON" position but don't start the engine. Leave the key on for three seconds. Turn the key back to the "OFF" position. Repeat this two more times. This will pressurize the system. Turn the key off and check for leaks.

Items you will need

  • Slotted screwdriver

  • Wrench set

  • Pliers

  • Ratchet and socket set

 How to Replace the Fuel Injectors on a Cummins 24V

Park the vehicle and allow the engine to cool. Open the hood. Place a step ladder in front of the vehicle to reach the engine.

Remove the valve cover located on the top of the engine by removing the bolts. The valve cover has a Cummins decal on the top. Place the valve cover aside.

Remove each fuel-supply line. These are gold-colored lines that feed into the engine. These require a 3/4-inch wrench. The injector closest to the firewall may require a crows-foot wrench to remove.

Remove the injector hold-down bracket using a ratchet and socket. The injector is located under the injector hold-down bracket. There are six injectors that need to be replaced. Replace injectors one at a time to avoid confusion.

Grasp the injector body with pliers. Gently pull the injector out of the engine.

Replace the injector with the replacement injector by sliding it into position. Replace the injector hold-down bracket and tighten the bolts using a ratchet and socket.

Continue with the remaining five injectors, one at a time.

Replace the fuel-supply lines into the injector housing. Use a 3/4-inch wrench to tighten each supply line. Confirm each line is tight to avoid fuel leaks.

Replace the valve cover and tighten the bolts using a ratchet and socket.

Confirm that all bolts are tight before starting the engine.

Items you will need

  • Step ladder

  • Ratchet and socket set

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