Testing Fuel Pressure: R33 Skyline Guide

If you're looking to test the fuel pressure on your Nissan Skyline R33, there are a few things you should know. First, it's important to have a basic understanding of how the fuel system works, including the fuel pump, fuel pressure regulator, and fuel injectors. Upgrading the fuel pump or injectors can affect fuel pressure, so it's crucial to ensure that the fuel pressure regulator is also upgraded to handle any increases in fuel flow. When testing, you'll want to measure the fuel pressure at the pump outlet and compare it to the relief valve setting. Additionally, checking for any restrictions or internal corrosion in the fuel lines is important, as these can impact fuel pressure. Finally, ensuring that the fuel pump is wired with a thick enough gauge to handle the required fuel pressures at high boost is essential. By following these steps and referring to your specific vehicle's manual, you can effectively test and maintain the fuel pressure in your Nissan Skyline R33.

Fuel pressure regulator installation

Installing a fuel pressure regulator (FPR) on your Skyline R33 is a moderately challenging task, but with the right tools and safety precautions, it can be done successfully. Here is a step-by-step guide on how to install an FPR:

Step 1: Safety and Preparation

Before beginning any work on your vehicle, it is important to take the necessary safety precautions. In this case, you will be working with fuel, so do not attempt to install the FPR after driving the car for an extended period, as the fuel system will be under pressure and hot. Consult your vehicle's repair manual for the correct procedure to release the fuel pressure from the lines. Typically, this involves unplugging the fuel cap and removing the fuel pump fuse, then cranking the car to release the pressure.

Step 2: Remove the Old FPR

The RB25 engine in the R33 Skyline has two FPRs. The one you need to change is located at the front, near the fuel rail. It is held in place by two screws, so use the correctly-sized screwdriver or ratchet to carefully remove them. Once the screws are out, carefully remove the fuel hose by loosening the clamps. Pull out the old FPR upwards and away from the fuel rail. There should only be a small amount of fuel spillage.

Step 3: Prepare the New FPR

Before installing the new FPR, check that you have all the necessary components, including the FPR itself, a mounting bracket, a pressure adjuster, locknut, and any required fittings or adapters. Refer to your FPR's manual to identify the correct fuel inlet and return ports, as these may vary depending on the make and model of the FPR. If your new FPR did not come with a new O-ring, consider replacing the old one to ensure a tight seal and prevent leakage.

Step 4: Install the New FPR

Now, you can begin installing the new FPR. First, attach any necessary fittings or adapters to the FPR, ensuring that O-rings are present and using high-quality thread sealant. Consult your FPR's manual to ensure correct installation of the fittings. If your FPR has a gauge port, you may choose to install a pressure gauge at this point. Once the FPR is prepared, attach the mounting bracket to the FPR using the provided screws and a suitable Allen key.

Step 5: Mount the FPR

Choose a suitable location for the FPR in the engine bay, ensuring it is at least 100mm away from any significant heat sources to prevent fires. Common mounting locations include against the chassis, onto or near the carburettor, or onto the intake manifold. Once you have decided on a location, mount the FPR using the provided screws and Allen key, ensuring that all plumbing is appropriately secured and is the correct size and chemical rating for your application.

Step 6: Connect the Fuel Lines

With the FPR securely mounted, you can now connect the fuel lines. Be extremely careful during this step to avoid fuel leaks. If you encounter any fuel leaks, switch off the engine immediately and rectify the leaks.

Step 7: Start the Engine and Check for Leaks

With the FPR installed and the fuel lines connected, you can now start the engine and check for leaks. Ensure that all fittings, lines, and mountings are secure and double-check that there are no fuel leaks. If there are no leaks, you can proceed to the final step.

Step 8: Adjust the Fuel Pressure

The final step is to adjust the fuel pressure to the correct specification for your vehicle. For a Nissan RB25 engine, the base fuel pressure with the vacuum hose disconnected should be around 43 psi or 3 Bar. When you reconnect the vacuum hose, the pressure will drop to around 34-37 psi. Adjust the fuel pressure by loosening the locknut and turning the adjuster with a suitable hex key.

Now, your new fuel pressure regulator is installed and ready for use! Always remember to refer to your vehicle's repair manual and the FPR's installation instructions for specific details pertaining to your particular vehicle and FPR.

Fuel pressure gauge installation

To install a fuel pressure gauge on your R33 Skyline, you'll need to take the following steps:

Firstly, source a suitable fuel pressure gauge. You will need a 60 or 100 psi gauge, a gauge fitting for a 3/8 inch fuel hose, and two 3/8 inch hose clamps. The fuel lines are actually 5/16 inch inside diameter hoses, but the 3/8 inch gauge fitting will fit. You can also use a full-sweep electric fuel pressure gauge or a Bluetooth OBD2 gauge display, which can be installed inside the car.

Next, release the fuel pressure from your fuel lines. You can do this by simply unplugging the fuel cap and pulling the fuel pump fuse, then cranking the car. Alternatively, some repair manuals suggest cranking the car, then removing the fuel pump fuse and waiting for the car to stall and turn off.

Now, you can remove the old fuel pressure regulator (FPR). On the RB25 engine, there are two FPRs, but the one you need to change is located at the front, near the fuel rail. It is held in place by two screws, so be careful when removing them so you don't strip the screws. Once the screws are removed, carefully remove the fuel hose. There should only be a small amount of fuel spillage.

At this point, you can start test-fitting the new FPR. You will need to refer to the FPR manual to determine the fuel IN/OUT ports. Once you have the FPR in the correct position, you can start finalising the fuel lines. Ensure that any fittings you use have thread sealant applied, and if using liquid sealant, let the car sit overnight so the sealant can cure.

Now, you can connect the vacuum hose from the manifold to the FPR. Before tightening the clamps, prime the fuel system and check for any fuel leaks. Make sure there isn't any pooled fuel anywhere before you start the engine.

Finally, adjust the fuel pressure to the correct level. The base fuel pressure on a Nissan RB25 with the vacuum hose disconnected should be around 43 psi or 3 Bar. When you reconnect the vacuum hose, it will drop to around 34-37 psi. Adjust the FPR by loosening the lock nut and turning the hex key to raise or lower the pressure.

Note: It is important to work with fuel safely and to minimise the risk of spills. Always refer to a qualified mechanic if you are unsure about any part of this process.

Fuel pump fuse removal

The fuel pump fuse is an essential component that protects the engine from electrical surges. When the fuel pump fuse blows, the engine may stall or fail to start, so it's important to know how to locate and remove it for inspection or replacement. Here's a step-by-step guide on fuel pump fuse removal:

Locating the Fuse Box:

• Refer to the driver's manual to identify the location of the fuse box and the specific fuel pump fuse. Modern cars often have multiple fuse boxes, so it's important to consult the manual to find the correct one.
• Common locations for fuse boxes include under the hood, under the kick panel (driver or passenger side), or behind the trunk wall carpet.

Removing the Fuse:

• Open the fuse box by removing the cover. The fuses may look identical, but they are often labeled with location numbers, colors, or diagrams for easy identification.
• Use the fuse puller tool attached to the fuse box cover or a small pointy nose plier to grip and pull the fuel pump fuse straight up for removal.
• Inspect the fuse by holding it up to the light and checking the metallic strip inside. If the strip is broken, the fuse is blown and needs to be replaced.

Replacing the Fuse:

• When replacing the fuel pump fuse, ensure you use a fuse with the correct rating. Most fuel pumps use 15 (Blue), 20 (Yellow), or 25 (Clear) amp fuses.
• Using a fuse with a lower rating may cause it to blow again, while a higher-rated fuse may not blow when it should, potentially damaging other components and creating a fire risk.

Additional Troubleshooting:

If you've replaced the fuse and it blows again, there may be other issues with the fuel pump or related systems. Some common causes of fuel pump failure include a bad connector at the pump, faulty wiring between the fuse box and pump, a bad crank sensor (CKP), or an inertia switch activation or fault. Further diagnostics and testing may be required to identify the specific issue.

Old FPR removal

To remove the old FPR from your R33 Skyline, you must first relieve the fuel system pressure. There are different methods depending on your model. For TBI models and multiport fuel injection systems, you can remove the fuel pump fuse or relay, start the engine, and let it idle until it stalls. For electronic fuel injection systems, cover the Schrader valve with a rag and carefully depress the valve with a screwdriver, then loosen the fuel filler cap.

Next, disconnect the negative battery cable.

Now you can access the old FPR. The RB25 engine has two FPRs, but the one that needs to be changed is located at the front near the fuel rail. It is held in place by two screws, so use the appropriately-sized screwdriver or ratchet to remove them carefully. Remove the fuel hose by loosening the clamps. Pull out the old FPR upwards and away from the fuel rail. You will notice it has a rubber o-ring, which normally would be replaced, but some new FPRs come with a new o-ring.

The next step is to pull the FPR from the fuel return line, which can get messy. Once the FPR and fuel lines are removed, you can start test-fitting the new FPR.

New FPR test fitting

The first step in test-fitting a new FPR is to identify its fuel inlet and outlet ports. These can usually be found in the FPR manual. Once you have located the correct ports, you can begin to connect the FPR to the fuel system.

If you are using an adjustable FPR, you will also need to connect a vacuum hose from the manifold to the FPR. This will allow the FPR to adjust the fuel pressure according to the manifold vacuum.

When test-fitting the FPR, it is important to ensure that it is securely mounted in the engine bay. In some cases, you may need to fabricate a bracket to hold the FPR in place. It is also crucial to check that the FPR does not interfere with any other components in the engine bay, such as the bonnet or hood.

Once the FPR is mounted in place, you can begin to connect the fuel lines. Be sure to use fuel injection hose and the correct fuel fittings and clamps to secure the connections. Refer to your FPR manual to identify the correct fuel inlet and outlet ports.

After the FPR is connected, you will need to add thread sealant to the fittings. It is recommended to let the car sit overnight to allow the sealant to cure fully. Once the sealant has cured, you can start the car and check for any leaks.

If there are no leaks, the next step is to adjust the fuel pressure. For a Nissan RB25 engine, the base fuel pressure with the vacuum hose disconnected should be around 43 psi or 3 Bar. When you reconnect the vacuum hose, the pressure will drop to around 34-37 psi. You can adjust the fuel pressure by loosening the lock nut and turning the adjustment screw with a hex key.

Frequently asked questions