Replacing Fuel Injector In A 92 Nissan 300Zx: Step-By-Step Guide

Replacing the fuel injectors on a 1990-1992 Nissan 300ZX can be done in one of two ways: the Dremel method or the conventional method of removing the intake manifold. The Dremel method involves using a rotary tool to grind away areas of the intake manifold that block the fuel injectors, allowing access without removing the intake plenum. However, this method can be messy and may result in metal shavings getting into various parts of the engine. The conventional method involves removing the intake manifold, providing easier access to the fuel injectors and facilitating other maintenance jobs. Both methods require careful handling of the fuel injectors and attention to specific details to ensure a successful replacement.

Removing the intake manifold

To remove the intake manifold, also known as the plenum or manifold collector, follow these steps:

First, decide whether you will be using the Dremel method or the conventional method. The Dremel method involves using a Dremel tool to grind away areas of the intake manifold that block access to the fuel injectors. This method is often quicker and easier, especially when replacing a single injector. However, 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 and provides easier access to the fuel injectors and fuel rail. It is also a good opportunity to perform maintenance on other components. However, it is more time-consuming and requires the replacement of the intake manifold gasket.

If you choose the Dremel method, use a Dremel tool or a similar rotary tool to grind away the parts of the intake manifold that block access to the fuel injectors. Be careful not to grind too far and create a leak in the intake manifold.

If you choose the conventional method, start by removing various vital engine components to access the intake manifold. Then, follow these steps to remove the intake manifold:

• Remove the 6 x 10mm bolts holding the fuel rail to the lower intake manifold.
• Remove the fuel rail's ground wire from the manifold (1x10mm bolt).
• Lift both sides of the fuel rail up as one unit.
• 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 careful not to obscure or damage the injectors. Do not use a vice, as it can damage the fuel rail.

By following these steps, you will successfully remove the intake manifold and gain better access to the fuel injectors for replacement.

Using the Dremel method

The Dremel method is one of two ways to replace a failed fuel injector on a 1990 Nissan 300ZX, the other being the conventional method of removing the intake manifold. The Dremel method involves using a Dremel tool (or similar rotary tool) to grind away areas of the intake manifold that block access to the fuel injectors, allowing their removal without taking off the intake plenum.

Advantages of the Dremel Method

• Often quicker and easier when replacing a single injector.
• Doesn't require replacement of the intake manifold gasket.

Disadvantages of the Dremel Method

• Metal shavings get everywhere.
• Potential for grinding too far and creating a leak in the intake manifold.
• Very difficult to remove the old injector without completely destroying it, even after modifying the plenum.

Tools Required for the Dremel Method

• Dremel tool with Flex Accessory (or other suitable rotary tool)
• Dremel #115 Grinding Tip & optional Polishing tips (for cosmetic purposes)
• Quality, brand new #2 Phillips Screwdriver (LONG)
• Ball-end hex tool (4mm or 5/32, preferably LONG with T-Handle — long 5/32" may be easier to find/same size)
• Shop Vac and Air Compressor
• Good Light (halogen tower lights or similar) and a Mini-Flex Flashlight
• 45-Degree Bent Nose Pliers (quality steel)
• Indumar FUSION TAPE (or PREMIUM 3M Electrical Vinyl Tape)
• Butane Torch (Great Tool) and Shrink Wrap Butt Connectors (or appropriate soldering tools)
• ScrewGrab Compound
• Magnet Tool (could be very useful)

Step-by-Step Guide to the Dremel Method

Step 1: Safety First

• This procedure involves working with a volatile fuel system, so take all necessary precautions.
• Have a suitable fire extinguisher on hand.
• Follow all safety precautions and warnings provided by Nissan and any supporting documents/links.
• Wear safety goggles as aluminium shavings can get into your eyes.
• Injectors have been known to shoot out if the rail has residual pressure, so be cautious.

Step 2: Diagnose Fuel Injector Issues

• Confirm that the injectors "click". When injectors open and inject fuel, they make a clicking sound. Take a long screwdriver while the car is running and put the end on the injector retainer cap. Put the handle end of the screwdriver to your ear and you should hear distinct clicks.
• If you do not hear clicks from an injector, further diagnosis will determine the solution.
• Even if all injectors are clicking, it's a good idea to go onto the next step to diagnose them further as they can click and operate even when out of spec.

Step 3: Test Fuel Injector Resistance

• Each injector can be tested for proper resistance from the ECU harness and directly across the injector terminals with a digital voltmeter.
• Nominal resistance is 10-14 ohms per FI. You need to test the ohmage between pin/wire #58 (common positive) and the following pins for each injector.
• A range of 12-14 ohms is more specifically accepted.

Step 4: Access the ECU

• Remove the wiring harness from the ECU.
• Remove the three additional screws that hold the ECU down, then remove the harness from the ECU with a 10mm socket.
• When reinstalling the ECU, take care when plugging in the harness and do not overtighten the 10mm bolt.

Step 5: Test the Injectors

• Use small test clips or thin paper clips to make contact with the ECU harness pin-holes. Don't be too rough to keep the harness in good shape for solid pin connections.
• Set your voltmeter to read OHMS, connect your red lead to lead 58 and black to FI lead you are testing. Be certain you are contacting the right leads.
• If you test an injector from the ECU harness and it returns a value within 12-14 ohms, you know your harness and injector are

Replacing the fuel injectors

There are two methods for replacing the fuel injectors on a 1992 Nissan 300ZX: the Dremel method and the conventional method of removing the intake manifold.

The Dremel Method

This method involves using a Dremel tool or a similar rotary tool to grind away the areas of the intake manifold that block access to the fuel injectors. This way, you can remove the injectors without taking off the intake plenum.

Advantages:

• Often quicker and easier, especially when replacing a single injector.
• Doesn't require replacing the intake manifold gasket.

Disadvantages:

• Metal shavings get everywhere.
• Potential for grinding too far and causing a leak in the intake manifold.
• It's almost impossible to remove an old injector without completely destroying it.

The Conventional Method

The conventional method involves removing the intake manifold (also known as the plenum or manifold collector) to access the fuel injectors. While this process is more time-consuming and requires replacing the intake manifold gasket, some consider it the proper way to replace injectors.

Advantages:

• No mess from metal shavings.
• Easier to remove injectors from the fuel rail as the rail can be taken out easily.
• Less labour-intensive than the Dremel method when replacing all injectors.
• Facilitates other maintenance jobs, such as valve cover resealing or timing belt service.

Disadvantages:

• More time-consuming, especially if it's your first time.
• Requires replacing the intake manifold gasket (approx. $9 USD).

Removing the Fuel Injectors

Once you've used one of the above methods to access the injectors, you can remove them. If you've removed the intake manifold, the easiest way is also to remove the fuel rail.

To remove the fuel rail:

• Take out the 6 x 10mm bolts holding the fuel rail to the lower intake manifold.
• 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.
• Unscrew 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 little washer.

Now, to remove the injectors, you can either:

A) Hit the injector with a hammer:

• Position an 11mm deep-well socket over the injector so that the socket's opening is touching the metal rim of the injector, but not the pintle (firing tip). Make sure the fuel rail is supported.
• Put a towel on the opposite side of the injector to catch it.
• Hit the injector with a hammer.

B) Remove the injectors from above:

• Relieve the fuel pressure and gain access to the fuel rail.
• Remove the pintle caps (2 Phillips screws on each cap).
• Using locking pliers, grip the tops of the injector head and twist while gradually pulling up and away from the engine.

Installing the New Fuel Injectors

Installing new fuel injectors is a delicate process that must be done carefully.

To install the new injectors:

• Install new OEM upper and lower O-rings. This step is crucial as injector O-rings are a compression type that can only be used once. Failure to replace them will cause a fuel leak, which can hydrolock the motor and cause engine failure.
• Lubricate the O-rings thoroughly with Vaseline or motor oil. Avoid silicone-based lubricants as they will damage the rubber.
• Insert the fuel injector straight into the rail, with the connector facing away from the rail and towards the outside of the car.
• As the upper O-ring hits the fuel rail and resists further insertion, gently twist the injector back and forth while applying more pressure. This will help prevent the O-rings from pinching.
• Continue until the injector fully seats in the rail. You may feel a pop or just a gentle landing.
• Do NOT force the injector in, and do not use tools. Use only your hands (or a towel for better grip). Forcing the injector can cause an O-ring to pinch and lead to a fuel leak.
• Be careful not to damage the little 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, hand-thread them, then tighten them down.

Reinstalling the fuel rail

To reinstall the fuel rail, first, make sure the fuel rail insulators are replaced. Then, install new OEM upper and lower O-rings. Lubricate the O-rings with Vaseline or motor oil (avoid silicone-based lubricants). Insert the fuel injector straight into the rail, ensuring the connector faces away from the rail and towards the outside of the car.

As the upper O-ring reaches the fuel rail, gently twist the injector back and forth while applying more pressure. This will help prevent the O-rings from pinching. Continue until the injector fully seats in the rail, which may be met with a pop or a gentle landing. Do not force the injector in.

Next, install the upper insulator (the small washer) around the peg sticking out of the top of P1 injectors. Set the cap screws in place and hand-thread them before tightening them down.

Finally, ensure you do not damage the peg sticking out of the top of the injector (on P1 injectors).

Testing the new injectors

Testing new injectors is important to ensure they are functioning correctly and to prevent damage to your engine. Here are some tests you can perform to check the operation of your new fuel injectors:

Listen to the Fuel Injectors

Identify the location of your fuel injectors. There is one per cylinder, typically a black plastic housing installed directly above the cylinder. Place the tip of a long screwdriver on the top of the fuel injector and place your ear on the handle of the screwdriver. You should hear a regular clicking sound as the injector cycles on and off. Compare the sound of all your injectors and note any differences. A problem with a dirty injector will be noticeable through this test.

Take a Resistance Reading

Turn off your vehicle and disconnect the electrical connector for the fuel injector. Use a multimeter to take a resistance reading. Check your vehicle's service manual or look online to learn the correct value (most fuel injectors should read between 10 and 18 ohms). All readings should be within the range suggested by the manufacturer, and they should be the same for all your injectors. If any resistance readings are off, the injector needs to be repaired or replaced.

Check for Leaking, Flow Rate, and Pattern

You can also test for leaking, flow rate, and pattern. For this, you will need to connect the injector to a battery and observe its operation. You can use a 9V or 12V battery, and a quick connection should be enough to test the injector. Observe if there is any leaking, and check the flow rate and pattern of the injected fuel. The pattern is important as a more atomized spray will mix better with the air and ignite more evenly.

Flow Rate Test

To test the flow rate, you will need to set up a pump with a known pressure (e.g., 50 psi) and a measuring device like a flask with graduations of known value. Activate the injector over the flask for a set time (e.g., 5 or 10 seconds) and then calculate the flow rate. All injectors should have a similar flow rate, as a significant difference can cause the engine to run too rich or too lean, leading to poor performance and potential damage.

Frequently asked questions