Replacing Optimax Fuel Injector Filters: Step-By-Step Guide

The Optimax air and fuel injection system is a complex mechanism that requires regular maintenance and servicing to ensure optimum engine performance. While the system is designed to supply metered air and fuel, it also lubricates the bearings and cylinder walls. This multi-functionality makes it susceptible to residue buildup and corrosion, which can lead to engine performance issues. To prevent this, it is recommended to replace the tank-to-engine fuel lines annually and clean the fuel injector and air injectors regularly. When it comes to replacing the fuel injector filters, it is important to have the right tools and follow a detailed procedure, as outlined by several online forums and service providers.

Removing the fuel injectors

Firstly, depressurise the fuel and air systems via the Schrader valves on the fuel rails, starting with the air side. If your engine has not been run for at least 8 hours, this step may not be necessary, but it is still recommended to remove the caps and check.

Next, remove the injector hold-down Allen screws and pull the fuel injectors from the rail. You will need to remove the two nuts that hold the rail to the cylinder head, then carefully slide the fuel rails off, ensuring the direct injectors remain in the head.

Some direct injectors may be difficult to remove, so be patient, rotate them, and be prepared for them to suddenly release. Make sure you have a firm grip, as dropping one could be costly.

Once you have removed the direct injectors, mark their location (cylinder number) on the bottom side of the connector (facing the head) with a Sharpie. It is also recommended to bag each direct injector and mark the bag as an extra measure.

Cleaning the fuel injectors

The fuel injectors of the Optimax engine should be cleaned at least once a year, especially if fuel-related problems have occurred. This is because maintenance and fuel-related issues are the main cause of engine performance problems in Optimax engines.

To clean the fuel injectors, you will need to first remove the fuel injectors and the fuel rail they sit on. To do this, follow these steps:

• Depressurise the fuel and air systems via the Schrader valves on the fuel rails, starting with the air side first. If your engine has not been run for at least 8 hours, this step may not be necessary, but it is still recommended to check and relieve the pressure.
• Remove the injector hold-down Allen screws and pull out the fuel injectors from the rail.
• Remove the nuts holding the fuel rail to the cylinder head and carefully slide the rail off, ensuring that the direct injectors remain in the head.
• Mark the location of each direct injector (e.g. "cyl 1, 2, etc.") on the bottom side of the connector, so you know which cylinder they came from.
• Pack the injectors and fuel rail according to the instructions provided by the cleaning service.
• Send the injectors and fuel rail for professional cleaning and flow testing.

Once the cleaning and testing are complete, you can reinstall the fuel injectors and fuel rail by following the removal process in reverse. It is important to note that your work area, hands, and tools must be clean and free of dust, dirt, grime, and debris during the reinstallation process. Additionally, make sure to replace any removed radius head tie wraps with exact replacements—common tie wraps are not suitable substitutes.

• It is recommended to use a bona fide, OEM Mercury Service Manual for your specific engine model when removing and installing the fuel injectors and fuel rail.
• When removing the fuel injector connectors, depress the metal retaining clip from the backside.
• Be cautious when removing the plastic retainer "ears" to prevent breaking them.
• When removing the direct injectors, be patient, rotate them while pulling straight out, and have a firm grip as they can be difficult to remove.
• During the reinstallation process, coat the o-rings of the direct injectors with oil.
• Torque all fasteners to the proper specifications as per your service manual.

By regularly cleaning and maintaining your Optimax fuel injectors, you can help ensure optimal engine performance and avoid costly repairs in the future.

Reinstalling the fuel injectors

Before reinstalling the fuel injectors, ensure your work area, hands, and tools are clean and free of dust, dirt, grime, and debris.

First, install the reed blocks to the reed plate. Use an accurate inch-pounds torque wrench to torque the fasteners to the proper specifications per your service manual.

Next, liberally coat the o-rings of the direct injectors with oil. Install the direct injectors by hand, ensuring they are placed in the correct location as marked by Don.

Then, install the fuel rails. Torque the nuts holding the fuel rails in place to the proper specifications.

Now, connect the fuel injector connectors. Depress the metal retaining clip from the backside to connect.

After that, connect the direct injector (DI) connectors. A small screwdriver or right-angle pick tool may be helpful in releasing connector retaining tabs.

Once all the connectors are in place, move on to the injector harness. Release the four "Christmas tree" style wiring harness retainers from the brackets surrounding cylinders 2/6 and 1/5 side injectors. Use an auto-body trim tool to detach these retainers from the brackets.

Next, connect the water pressure and pitot sensor connectors. Note that 3L models will only have water pressure on the coil plate.

Then, open the double hose retainer and snip the radius head tie wrap on the backside of the compressor. Ensure that the air-line is attached to the rails.

Now, lift and move the injector harness out of the way. Follow the fuel hoses from the rails to their origin on the VST. Cut the Oetiker clamp and clamp the hose prior to removal to minimize fuel spillage. Remove the hose from the nipple and drain any fuel into a suitable container. Repeat for the starboard fuel rail.

Finally, reconnect the cooling lines to the strainer and the block. Ensure all lines, connectors, and hoses are secure before starting the engine.

Removing the fuel rail

The process of removing the fuel rail will differ depending on the vehicle. The following is a general guide, but for specific instructions for your vehicle, consult the relevant manual or a mechanic.

Before starting, ensure the fuel system is not under pressure. The fuel system is under pressure even when the engine is off, so release the fuel pressure before servicing the fuel rail.

Step 1:

Remove the gas cap and the fuel pump fuse. Start the engine and run the vehicle until it dies. Repeat this process until the vehicle no longer starts.

Step 2:

Disconnect the negative battery cable. This step is very important, so be sure not to skip it.

Step 3:

Remove the air inlet hose at the throttle body and airbox. You will also need to disconnect the fuel line latch clip and fuel line at the fuel rail. Note that a special tool may be required for this step.

Step 4:

Remove the vacuum/vapor lines at the throttle body. At this point, you should also disconnect all electrical connectors at the fuel injectors. Push the red-coloured slider away from the injector and, while pushing the slider, depress the tab to remove the connector from the injector.

Step 5:

The factory fuel injection wiring harness should be tagged (e.g. INJ 1, INJ 2) for injector positions. If the harness is not tagged, be sure to mark them yourself before removing.

Step 6:

Disconnect any remaining electrical connectors at the throttle body.

Step 7:

Remove all ignition coils.

Step 8:

Remove the four fuel rail mounting bolts. Gently rock and pull the left side of the fuel rail until the fuel injectors start to clear the holes in the head. Repeat on the right side. Continue alternating between the left and right sides until all injectors have cleared the head holes.

Step 9:

Remove the fuel rail (with injectors attached) from the engine. Be careful not to bend or kink any tubes during this process.

Reinstalling the fuel rail

To reinstall the fuel rail, you will need to follow the disassembly process in reverse.

Firstly, ensure your work area, hands, and tools are clean and free of dust, dirt, grime, and debris.

Next, liberally coat the o-rings of the direct injectors with oil. You can use Premium Plus oil or similar.

Now, you can install the direct injectors by hand, ensuring you place them in the correct location as marked by the service technician.

After this, you can reinstall the fuel rails. Ensure you torque all fasteners to the proper specifications per your service manual.

Then, reconnect the cooling lines to the strainer and the block.

Now, you can reconnect the fuel hoses to the rails and the VST. Ensure you clamp the hoses before removing the clamps to minimize fuel spillage.

Next, reconnect the water pressure and pitot sensor connectors.

Reattach the injector harness, ensuring the four 'Christmas tree' style wiring harness retainers are secured to the brackets surrounding cylinders 2/6 and 1/5 side injectors.

Now, you can reconnect the fuel injector connectors.

Finally, you can reinstall the upper and lower cowling and any other components you removed during disassembly.

Once you have completed these steps, you can perform an oil pump prime and confirm that your engine is running smoothly.

Frequently asked questions