Nissan Fuel Injector Replacement

Vehicles covered: Nissan Pathfinder ’96-2000, Nissan Frontier ’97-’04, Nissan Xterra 2000-’02, Nissan Quest ’99 – ’02, Infiniti QX4 ’97 – 2000.

Introduction

Over thousands of miles of service fuel injectors wear and the small holes through which fuel is sprayed can become clogged with sooty deposits or contaminated fuel. On many vehicles it’s not particularly difficult to replace the injectors, but it does take time as they are usually buried quite deep. That’s why it can be prohibitively expensive to have the job done by a dealership or specialist shop. The alternative is to do it yourself.

This guide goes through the steps involved in replacing the injectors in Nissan’s VG33 3.3 liter V6. Some of the details are specific to that engine, but the general principles will apply to many other engines.

List of headings

Fuel injection system overview

Preparation

Upper inlet manifold removal

Fuel rail removal

Injector removal and replacement

Fuel rail re-installation

Fuel rail and manifold re-installation

Fuel injection system overview

Before launching-in it’s helpful to have an understanding of the key components of the fuel delivery system.

Fuel is delivered to the injectors by a pump, usually in the gas tank, capable of delivering a high volume of gas very quickly. To ensure there’s an adequate reserve of gasoline for starting the engine and for sudden acceleration, the pump supplies a “rail” or pipe where the gasoline is held under very high pressure. The injectors are connected directly to this rail and contain a small electrical actuator that opens and closes rapidly to allow a precisely metered volume of fuel into the combustion chamber.

Excess fuel – fuel not needed to maintain pressure in the rail – returns to the tank via a low pressure line.

Preparation

Safety is paramount, especially when working on the fuel system. Park the vehicle on level ground in a well-ventilated, well-lit area and position a dry powder fire extinguisher close by. Keep a supply of rags close by for mopping up spills and for blocking open orifices in the lower inlet manifold.

Relieve pressure in the fuel rail by pulling the fuel pump fuse and running the engine until it stalls. If you don’t do this you’ll have gasoline spraying around your garage and perhaps in your eyes the moment you start disconnecting the high pressure fuel supply line. Equalize pressure in the gas tank by loosening or removing the cap.

Disconnect the battery by removing the negative (black) terminal from it’s post.

Keep a camera close by and take lots of photos as you go, from multiple angles. They can be invaluable when you’re trying to remember how cables or hoses were routed!

Use Ziploc bags or yoghurt pots to retain all the fasteners and hose clamps that are going to come off the engine. Label each bag or pot so you know where each screw, nut or bolt came from.

Protect the paint on your fenders by covering them with old blankets or towels.

Upper inlet manifold removal

On most engines the air intake system must be removed to get access to the fuel rail. The Nissan VG33 engine uses a two-part inlet manifold under the air intake and throttle body: the upper half of this needs to come off.

As you look at the manifold you’ll see there are many hoses attached. This all need to come off, although the other end should be left connected. Take lots of photos and label each hose by with masking tape.

Here are the steps to follow:

1. Drain the coolant from the radiator. This needs doing because the manifold receives coolant through tow hoses at the rear of the engine. Disconnect these.
2. Disconnect hoses joining the the intake duct that connects the filter box to the upper inlet manifold. Then remove the intake duct itself.
3. Unplug the two electrical connectors at the side of the throttle body.
4. Disconnect the throttle and cruise control cables from the pulleys they run over on the side of the throttle body. Do this by lifting and rotating the pulleys to create some slack in the cables, then they are easily unhooked.
5. Undo the two bolts holding the throttle adjustment bracket to the top of the manifold and lift the cables out of the way. (Avoid any temptation to move the adjustment nuts!)
6. Undo the flange nut on the EGR tube. It’s probably quite corroded so use plenty of penetrating oil and let it soak. (This avoids disconnecting the EGR valve from the manifold.)
7. Remove the brake booster hose.
8. Take off the distributor cap to create more room for lifting the manifold.
9. The electrical harness fastened to the manifold needs removing. Undo the three bolts holding it in place.
10. Label then remove the spark plug boots from cylinders 2 and 4 and remove the wire from #6.
11. Use a hex socket wrench to undo the bolts securing the manifold and lift it away, checking that nothing has been left connected.
12. Cover the open ports with lengths of duct tape to prevent any small parts or tools from dropping down inside.

Fuel rail removal

Removing the manifold exposes the fuel rail. You’re going to take this off the engine so you can work on it at a bench. These are the steps to follow:

1. Disconnect the electrical harness from the six injectors.
2. Disconnect the high pressure feed and low pressure fuel return lines from the rail.
3. A plastic cap covers the top of each injector, and this is held in place by two Phillips screws. Loosen but do not remove these screws. (This is because it’s easier to undo the screws while the rail is held firmly in place.)
4. Using a hexagonal socket wrench, undo the four bolts holding the rail in place.
5. Lift the rail out, making sure to retrieve the four plastic spacers underneath the bolts.
6. If you plan on replacing the injector seals, lift them out too. Cover the open ports with duct tape.

Injector removal and replacement

Working at a bench, follow these steps to replace the fuel injectors:

1. Remove the Phillips screws holding the plastic cover over each electrical connector (top) end and lift the cover off.
2. Ease out each injector from it’s pocket in the rail, by wriggling the plastic body of the electrical connector.
3. Pull out the washer at the bottom of each pocket.
4. With the rail stripped down, clean each pocket to ensure no debris remains and inspect it carefully for any signs of corrosion. If any are found the rail should be replaced rather than reused.
5. Take the new injectors and fit the O’rings, lubricating with gasoline to help them slide into place.
6. Put a washer at the bottom of each pocket in the fuel rail, then push each injector into place and reattach the plastic cover with the two Phillips screws.

Fuel rail and manifold re-installation

1. Remove the tape you placed over the injector ports and mount the rebuilt fuel rail assembly on the engine, carefully ensuring each injector is fully home in its housing.
2. Replace the bolts and the spacers that go under the rail.
3. Reconnect the fuel lines and plug in the electrical connectors at the top of each injector.
4. Remove the tape blocking the inlet ports. Reinstall the manifold, using a new gasket and torquing bolts as specified in the workshop manual.
5. Reconnect spark plug wires and the electrical harness mounted to the manifold.
6. Refit the hoses that were disconnected during dis-assembly, including the coolant hoses.
7. Reconnect the EGR tube.
8. Replace the inlet duct and reattach the hoses that connect to it.
9. Reattach throttle and cruise control cables and the throttle body electrical connectors.
10. Refill with coolant.
11. Check pots and/or Ziploc bags for any leftover fasteners.
12. Reconnect the battery.

Refer to the photos taken during dis-assembly to verify that everything has been put back correctly. When satisfied that nothing has been overlooked turn the ignition key to ‘Run’ and allow the pump to charge the fuel line. Then crank the engine. It may take a few seconds to fire. Check that it’s running smoothly then turn it off and look around under the hood – use your nose too – for leaks.

Save money, do it yourself

Have fuel injectors replaced is expensive, unless you do it yourself. While it may seem daunting initially, given the number of engine pieces that need removing, it’s a job that most home mechanics can handle. The key is to go carefully, taking photos along the way to guide reassembly.