A few months ago I posted a how to guide on installing a Walbro 255 fuel pump into the Nissan 240sx. As I noted the Walbro has a tendency to overflow the stock fuel pressure regulator on the 240sx and cause the injectors to operate at a higher fuel pressure which ultimately richens the fuel mixture. An overly rich fuel mixture harms gas mileage, robs horsepower and can even damage the motor. This tutorial walks through the steps necessary to install a Nismo Adjustable Fuel Pressure Regulator and properly set the fuel pressure on the Nissan 240sx with a CA18DET swap.
(Note that this process is similar for all Nissan motors with the exception of the base fuel pressure. The base fuel pressure can be found in the FSM for your motor.)
Depressurize the fuel system
First things first, the fuel system needs to be depressurized. With the car parked on level ground, the transmission in neutral and the parking brake engaged, open up the hood and locate the EGI Pump fuse in the fuse box near the battery. Remove this fuse and start the car. The car will idle for a short period and then will die. The fuel system is now depressurized.
Remove this fuse and start the car in order to depressurize the fuel system.
Remove the factory fpr
Now locate the factory fuel pressure regulator near the firewall at the end of the fuel rail. Go ahead and remove the vacuum line from the top of the fpr and then the fuel return line from the bottom. With these lines removed you can now remove the two screws that hold the fpr to the fuel rail. Use an angled philips head screwdriver or a pair of needle nose pliers to gently back the screws out. Take your time here as these screws strip easily.
(Note: Even with the fuel system depressurized there may still be fuel present in the rail and lines. Have a few rags handy just in case.)
Install the new fpr
The Nismo fuel pressure regulator will install into position where the old fpr was removed with one exception. The return line on the Nismo unit may need to be slightly bent downward to line up with the existing fuel return line. Once installed into the fuel rail, go ahead and install the fuel return line onto the bottom of the Nismo unit as well as the boost/vacuum line on the top. Use new clamps if necessary to secure these lines.
Pictured above is the Nismo Adjustable Fuel Pressure Regulator installed onto the CA18DET’s fuel rail. Note the adjustment screw on the top.
Setting the fuel pressure
The last thing left to do is to set the base fuel pressure on the new fpr. On the CA18DET this pressure should be 36.3 psi or 2.55kg/cm2. In order to set the pressure you will need two items: a fuel pressure gauge and a small length of medium gauge wire. A basic fuel pressure gauge can be purchased at any autoparts store and should be t’ed into the pressure line going into the fuel rail. The pressure line is the line that extends from the fuel filter on the passenger’s side strut tower and then continues to the fuel rail.
Circled in red is the sending unit for an electric fuel pressure gauge. Notice that I tee’d the gauge into the pressurized fuel line using a brass t.
With the gauge installed we are now going to wire the fuel pump to stay on continuously without starting the car. First take the short length of medium gauge wire and strip its ends. Then bend the wire in half and insert each stripped end into the two center ports on the EGI fuse sockets. (These are the two closest together and are highlighted in the pictures below) Next place the key in the ignition and place it in the on position. (Do not start the car) The fuel pump will turn on and remain on. At this point, go to the Nismo fpr and using a ten millimeter wrench, loosen the lower nut on the adjustment screw. While looking at the fuel pressure regulator turn the adjustment screw (counter clockwise to reduce pressure and clockwise to increase pressure) until the fuel pressure gauge reads 36.3 psi or 2.55kg/cm2 exactly. Once this value is satisfied, tighten the lower nut to lock the adjustment screw and then turn the ignition off. Finally, remove the jumper wire from the EGI fuse port and reinsert the fuse. The new fpr is now adjusted and ready for action.
This small wire will be used to jump the connection in the fuel pump fuse (EGI).
The jumper wire should be inserted into the EGI fuse block as shown above.