Fuel Injector Replacement: A Step-By-Step Guide For 300Zx Owners

Replacing the fuel injectors on a Nissan 300ZX is a complex task that requires a good amount of automotive knowledge. The fuel injectors regulate the amount of pressurised fuel used for each engine cycle, and there is one injector per cylinder in the engine. When replacing the fuel injectors, it is recommended to use high-quality, OEM parts to ensure even power across the engine and a proper air-fuel mixture for all cylinders. This should result in a smooth run.

There are two methods for replacing the fuel injectors: the Dremel method and the conventional method of removing the intake manifold. The Dremel method involves using a Dremel tool to grind away areas of the intake manifold that obscure the fuel injectors, allowing them to be removed without taking out the intake plenum. However, this method can create a mess of metal shavings and potentially cause leaks in the intake manifold if the grinding goes too far. The conventional method involves removing the intake manifold, which provides easier access to the fuel injectors and facilitates other maintenance jobs. It is a more time-consuming process and requires the replacement of the intake manifold gasket.

The cost of replacing the fuel injectors on a Nissan 300ZX ranges from $1,623 to $2,051, including labour and parts. It is not recommended as a DIY job due to the risk of fire and the complexity of the repair process.

Removing the intake manifold

First, it is important to relieve the fuel pressure and gain access to the fuel rail. Remove the pintle caps (2 Phillips screws on each cap). Be cautious, as the original screws are Phillips head screws that can easily strip. To avoid this, use the properly sized screwdriver and gently tap it into place with a hammer. If the screws strip, try using locking needle-nose pliers to remove them.

Next, remove the 6 x 10mm bolts holding the fuel rail to the lower intake manifold. Then, remove the fuel rail's ground wire from the manifold (1 x 10mm bolt). At this point, you can lift both sides of the fuel rail as one unit.

Now it is time to remove the caps securing the injector to the fuel rail (2 x Phillips screws). Be careful not to damage the top of the injector or lose the small washer. Turn the rail upside down and support it over an opening, being cautious not to damage the injectors or obscure them.

Position an 11mm deep-well socket over the injector so that the socket's opening is touching the metal rim of the injector. Ensure it is not touching the pintle and that the fuel rail is supported by something other than the injector. Place a towel on the opposite side of the injector to catch it. Now, tap the injector with a hammer.

If you have removed the fuel rail, it is easiest to remove the injectors by tapping them out from underneath. If you are unable to remove the fuel rail, you can remove the injectors from above, but this will likely damage the injector.

The removal of the intake manifold will also facilitate the removal of various related components, making future plenum removal jobs significantly easier. It is also an opportunity to perform other maintenance jobs, such as valve cover resealing or timing belt service.

After completing the necessary maintenance and repairs, carefully reinstall the intake manifold and all associated components. Ensure all connections are secure before starting the engine.

Using the Dremel method

The Dremel Method is a handy way to replace fuel injectors in a 300ZX without removing the plenum. Here's a step-by-step guide on how to do it:

Step 1: Prepare the Necessary Tools and Materials

Before you start, make sure you have the following tools and materials ready:

• Dremel brand rotary tool with a #225 Flex-Shaft attachment
• Tungsten carbide cutter bit (#9901 or similar metal grinding bit)
• Phillips screwdriver (for old screws)
• Allen wrenches, preferably ball-end Allen wrenches
• Two 5mm x 14-16mm x 0.8mm stainless steel Allen screws per injector
• Shop Vac
• Replacement injector and O-rings
• PB Blaster, WD-40, and Vaseline
• Light source
• Torque wrench
• Butane torch
• Screwdriver
• Pliers
• Safety goggles

Step 2: Relieve Fuel Pressure and Remove the Throttle Cover

Start by relieving the fuel pressure. Then, use a 5mm Allen wrench to remove the four cap screws that hold the throttle cover. For injector number one, loosen and set aside the throttle and cruise control cables, and the throttle bracket.

Step 3: Grinding the Plenum

Using the Dremel tool with the grinding bit, grind the plenum area above the injector cap screws. This will give you better access to the screws. Use a Shop-Vac to suck up the metal filings as you grind, and periodically check your progress to ensure you don't grind too deeply.

Step 4: Remove the Injector Cap Screws

Once you have ground away enough material, use a screwdriver or pliers to remove the injector cap screws. Be careful, as the injectors may shoot out if there is residual pressure in the rail. Also, make sure to keep track of any small parts, such as the half-circle washer under the retainer cap.

Step 5: Remove the Old Injector

After removing the cap screws, you can now take out the old injector. This may require some twisting and pulling, and you may need to break the seal first. Soak the injector in PB Blaster overnight to make removal easier.

Step 6: Clean and Prepare the Injector Hole

Before installing the new injector, clean the injector hole thoroughly to remove any residue. You can use throttle cleaner for this step.

Step 7: Install the New Injector

Coat the new injector's O-rings with Vaseline and squirt a little WD-40 into the lower plenum socket where the injector seats. Then, insert the new injector, making sure the O-rings and the rubber gasket are properly seated.

Step 8: Reinstall the Injector Cap and Screws

Place the injector cap over the new injector, making sure the half-circle washer is in place. Tighten the Allen screws by hand, then give them an extra turn with the torque wrench, being careful not to overtighten.

Step 9: Final Checks and Clean-up

Double-check that all connections are secure and components are properly seated. Clean up any remaining metal shavings and residue, and dispose of them safely.

The Dremel Method provides an innovative, time-saving, and cost-effective approach to replacing fuel injectors in a 300ZX. By grinding away a small portion of the plenum, you can access the injector cap screws without the need to remove the entire plenum, making the replacement process much simpler and faster. Remember always to wear safety goggles and take the necessary precautions when working with power tools and fuel systems.

Replacing the fuel rail

The fuel rail is a component of the fuel delivery system in a car. Replacing the fuel rail on a Nissan 300ZX can be done in two ways: the Dremel method or the conventional method of removing the intake manifold. Here is a step-by-step guide on how to replace the fuel rail on your 300ZX using the conventional method:

Step 1: Remove the Intake Manifold

First, remove the intake manifold, also known as the plenum or manifold collector. This process can be time-consuming as it involves removing and reinstalling various vital engine components.

Step 2: Remove the Fuel Rail

Once the intake manifold is removed, you can access the fuel rail. Remove the 6 x 10mm bolts holding the fuel rail to the lower intake manifold. Then, remove the fuel rail's ground wire from the manifold (1 x 10mm bolt). Lift both sides of the fuel rail up as one unit.

Step 3: Remove the Injectors from the Fuel Rail

Before removing the injectors, place a towel on the opposite side to catch them. Then, remove the caps securing the injectors to the fuel rail (2 x Phillips screws). Be careful not to damage the top of the injector or lose the small washer. Turn the rail upside down and support it over an opening, being careful not to obscure or damage the injectors. Do not use a vice as it can damage the fuel rail. Position an 11mm deep-well socket over the injector, ensuring it does not touch the pintle (firing tip). Hit the injector with a hammer to dislodge it from the fuel rail.

Step 4: Prepare the New Fuel Rail

If you are installing a new fuel rail, it is important to lubricate the O-rings with Vaseline or motor oil. Avoid using silicone-based lubricants as they can deteriorate the rubber O-rings. You may also apply lubricant to the inside of the fuel rail.

Step 5: Install the New Fuel Rail

Insert the fuel injectors into the new fuel rail, ensuring the connectors face away from the rail and towards the outside of the car. Gently twist the injectors and apply pressure until they are fully seated in the rail. Do not force the injectors in, as this can cause an O-ring to pinch and lead to a fuel leak. Install the upper insulator (washer) around the peg on the top of the injector. Finally, set the cap screws in place and tighten them down.

Optional Upgrade: Polar Engineering Billet Fuel Rails

Polar Engineering offers an upgraded fuel rail kit for the Nissan 300ZX Z32 that allows the use of modern top-feed injectors. This kit includes fuel rails, injector mounting plates, spacers, clamps, and hardware. The fuel rails are priced at USD 650.00 shipped within the USA.

Disconnecting the fuel injector

First, you need to decide on a method for accessing the fuel injectors. There are two common methods: the Dremel method and the conventional method of removing the intake manifold. The Dremel method involves using a rotary tool to grind away parts of the intake manifold that block access to the fuel injectors. This can be quicker and easier, especially when replacing a single injector, but it creates metal shavings and carries the risk of grinding too far and damaging the intake manifold. The conventional method involves removing the intake manifold, which is a longer process but is less messy and makes it easier to remove injectors from the fuel rail.

If you choose the Dremel method, be sure to cover your eyes and mouth to protect yourself from metal shavings. Grind away the necessary parts of the intake manifold, being careful not to damage any other components. Once you have access to the fuel injectors, you can move on to the next steps.

If you choose the conventional method, start by removing the intake manifold. This is a lengthy process that involves removing various vital engine components. You may need to drain the coolant and oil and replace the intake manifold gasket. Once the intake manifold is removed, you will be able to access the fuel injectors.

The next steps are the same for both methods. Remove the 6 x 10mm bolts holding the fuel rail to the lower intake manifold. Then, remove the fuel rail's ground wire from the manifold (1 x 10mm bolt). Lift both sides of the fuel rail up as one unit. Now you will be able to access the fuel injectors.

Remove the caps securing each injector to the fuel rail. There are 2 x Phillips screws per injector. Be careful not to damage the top of the injector or lose the small washer. Now you are ready to remove the injectors themselves.

Position an 11mm deep-well socket over the injector so that the opening is touching the metal rim of the injector, but not the firing tip. Make sure the fuel rail is supported, as you will need to hit the injector with a hammer to dislodge it. Place a towel on the opposite side of the injector to catch it when it comes loose.

With the injector disconnected, you can now install a new one. Be sure to replace the fuel rail insulators and lubricate the new injector's O-rings before inserting it into the fuel rail.

Installing new fuel injectors

Step 1: Prepare the necessary tools and materials

Before you begin, make sure you have all the necessary tools and materials, including a new fuel injector, new OEM upper and lower O-rings, lubricant (such as Vaseline or motor oil), a towel, and any other recommended safety gear.

Step 2: Access the fuel injectors

To access the fuel injectors, you will need to remove the intake manifold, also known as the plenum or manifold collector. This process can be time-consuming and may involve removing various engine components, such as draining the coolant and oil. However, some vehicles may have plastic intake manifolds that do not contain oil or coolant passages, making this process easier.

Step 3: Remove the old fuel injector

Once you have accessed the fuel injectors, you will need to disconnect the old fuel injector from the fuel rail and electrical connector. This can be done by removing the caps securing the injector to the fuel rail using a Phillips-head screwdriver. Be careful not to damage the top of the injector or lose any small parts, such as the washer.

Step 4: Install the new fuel injector

• Install the new OEM upper and lower O-rings. This step is crucial and cannot be skipped, as injector O-rings are compression seals that can only be used once.
• Lubricate the O-rings thoroughly with Vaseline or motor oil, avoiding silicone-based lubricants as they can deteriorate the rubber. You can also apply a small amount of lubricant to the inside of the fuel rail.
• Insert the new fuel injector straight into the rail, ensuring that the connector faces away from the rail and towards the outside of the car.
• Gently twist the injector back and forth while gradually applying more pressure to help prevent the O-rings from pinching.
• Continue until the injector fully seats in the rail, which may be indicated by a pop or a gentle "landing" sensation.
• Do not force the injector, as this can cause an O-ring to pinch and lead to a fuel leak. Instead, use your hands or a towel for better grip if needed.
• Be careful not to damage the peg sticking out of the top of the injector (on P1 injectors).
• Install the upper insulator (washer) around the peg on P1 injectors.
• Set the cap screws in place and hand-tighten them before using a screwdriver to snugly secure them.

Step 5: Reassemble and test

After installing the new fuel injector, carefully reassemble all the components that were removed to access the fuel injectors. Once everything is back in place, start the engine and check for any leaks or issues. If you notice any problems, re-inspect your work and ensure that all connections are secure and all components are properly installed.

Frequently asked questions