My Pro Street

How to Install Injectors in a RB25

John Huh

As part of our RB25 Engine Swap Guide, we’ll be taking a look at one of the hallmarks of aftermarket modifications with a set of 720cc Deatschwerks High Impedence Injectors. We prefer these injectors over other competitors because these injectors are designed as true bolt in applications, with little need of conversion harnesses, which only complicate your engine bay wiring.

 

If you need to size your injectors first, check the link below for proper fuel injector sizing calculation. To begin our How to Install Injectors writeup, let’s continue on.

How to choose Aftermarket Injectors

These injectors are top feed and high impedence which makes them perfect for our application, however since the stock fuel injectors are side feed, we’ll need an aftermarket fuel rail to complete the install. We’ve chosen a JGY unit for this install, but we couldn’t honestly recommend this rail for anyone to purchase new.

While the fitment of the injectors is decent, the mounting brackets and the overall length of this rail give us the impression that this RB25 rail is not designed for the motor specifically but instead a core that can be cut to length and sold as needed. While this is a cost effective manufacturing style, it’s not ideally what you want in your turbo inline six motor. We will get into the other issues of this JGY rail later on in the writeup.

The RB25DET is an inline six turbocharged motor that operates at a static 43 psi at the rail without the use of vacuum. After the installation of our Deatschwerks DW300 fuel pump, our pressure has skyrocketed to 62 psi at the rail, which makes part throttle and idle tuning absolutely impossible.

To solve this problem, we’ll be installing an aftermarket fuel pressure regulator to help curb the excess pressure in our rail and get us closer to something reasonable.

How To Install Top Feed RB25 Injectors

Parts you will need to complete this job.

Begin by disconnecting the negative terminal on your battery, and opening your gas cap and allowing pressure to escape your fuel system. Next we’ll have to undo the stock fuel system as a next step in our How to Install Injectors Guide.

Now undo the 12mm bolts that secure your stock rail to the head and disconnect your factory rubber return and feed lines, as these will be junked in favor of the stainless fuel line upgrades. When your rail is disconnected, lift the entire assembly out of the head and out of your engine bay.

Make sure to take care when doing this as you do not want to lose the fuel rail isolators that space your rail from your cylinder head. These isolators can be tricky to replace as your engine is not normally found here in the United States, so make sure you do not lose these plastic pieces.

You can also remove your stock fuel filter, whether is a KA24 unit or a Z32 unit as we will be installing a Red Horse Micron Fuel Filter inline of the fuel system.

Now locate your factory fuel feed and return lines because you will be using your Red Horse Compression Fittings to convert your slip on barb style of fuel line, to a AN fitting. Use a pipe cutter or handy metal crimp to cut the metal line as flat as possible, making sure to clean up any barbs or excess metal that may remain or hinder the compression fitting.

Use extreme caution when modifying these hard lines, you do not want to kink or damage them as repair will entail removal of the entire hardline from your car or cutting further back in your firewall for repair.

The S13 uses 1/4 inch size hardlines, make sure the brass fitting slides snugly over the line and compress the two ends together to create your seal.

Now with the return and feed lines cut and cleaned up, install your compression fitting by sliding the compression ring in between the conical ends and tighten the entire assembly down to complete the termination.

 

We will be converting the entire fuel system to -6 AN, so make sure this compression fitting is nice and tight. This fitting will also be the first ones to check once you start up your RB25.

Now install your top feed injectors into your aftermarket rail by lightly greasing the top of the injector orings, make sure you do not tear, bind or otherwise hinder the performance of your injector seals. Test fit your aftermarket rail and injectors before gently pushing them into place and re-installing the 12mm bolts.

If you haven’t already, make sure to plug in your injector clips to prevent any problems later on down the road when everything is tightened down. After your installation of your new top feed injectors is done, install your 90 degree 8th inch NPT fitting and your liquid filled fuel pressure gauge.
Mount your Aeromotive Drag Fuel Pressure Regulator and connect the -6AN lines to your feed and return respectively.

If you did not choose to install Deatschwerks top feed injectors, you may or may not require some injector wiring to convert your fuel injectors to the proper style of connector. MSD OBDI fuel injector clips are probably your best bet and can be found for around 30 dollars for a set of 6 pigtails.

Wiring of these injectors is extremely straightforward, just make sure to have the injector clip orientation consistent for all six new clips.

Use your -6 male to 3/8th pipe fittings now on either end of your rail,depending on where or how you want to run the lines, the other 4 swivels will comprise the rest of the fuel setup.

Once you have installed the new regulator and a fuel pressure gauge, turn engine on to check for any
leaks. We recommend double-checking to be positive that no leaks exist with extra special attention being paid to the compression fittings. If any sign of leakage should occur, IMMEDIATELY stop the engine and repair or remove the regulator.

 

If your motor is running now without any leaks or issues, re-connect your battery and start the car with the fuel pressure regulator disconnected from your motor. Using a 3/16 inch allen and a 7/16 inch wrench you can now adjust the pressure in your fuel rail.

Clockwise will raise your fuel pressure at idle and counter-clockwise will lower the fuel pressure. Once you have dialed in your RB, make sure to lock the jam nut securely and reconnect the vacuum line. Your fuel pressure WILL DROP around 10psi give or take once you connect this vacuum line. You are nearing the end of our How to Install Injectors guide, let’s make sure that you have the right sized injector.

How to choose the right sized injector??

We had to use 2 of the brackets as JGY did not properly machine their rail to take 3 mounting brackets. Further we had to use the factory isolators on the opposite side of the bolt to make things tight and secure.

You are now done with your top feed injector install! Here’s a few tips and tricks when troubleshooting if your RB isn’t behaving the way it should after this install.

Trouble Shooting Your Injector Install

1. Fuel Pressure Regulator can’t lower pressure.

Your feed and return on your regulator is backwards, switch the lines and try again.

The center screw inside the regulator has bottomed out inside and must be backed off.

2. Fuel Pressure Regulator can’t raise pressure.

Fuel pump Failure – make sure pump and relay are operational.

Inline fuel filter is clogged

Pump won’t make any more than that pressure, upgrade your fuel pump.

The center screw inside the regulator has been stripped and will not allow for adjustment.

3. Pressure rises, but not enough:

Your fuel pump is not sufficient, upgrade your fuel pump.

Increase the center screw adjustment but do not undo the screw.

Check the inline fuel filter and the filter on your pump

Remove the factory restrictor or fuel damper if applicable.

4. Regulator buzzes under boost:

This can occur at times when the fuel pump and manifold pressure oscillations overlap each other. You can remedy this issue by turning the center screw of your regulator or adjusting the base fuel pressure ever so slightly. If this does not improve the situation, return the regulator to us for an overhaul or replacement.

What we didn’t like about the JGY Rail.

We had to use 2 of the brackets as JGY did not properly machine their rail to take 3 mounting brackets and further we had to use the factory isolators on the opposite side of the bolt to make things tight and secure. Also the length of the rail makes it rather unsightly.

For the cost, a great option but not ideally our first choice for an aftermarket fuel rail in our RB25DET. 

Next up for our Project RB, we’ll be taking it to the dyno and dialing in our Apexi Power FC Commander to crack the 450whp mark!

You have now completed our How to Install Injectors guide, please let us know if you have any questions below!

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