How To Build A Honda Civic Ep3 Fuel Return System

We are constantly getting asked to help customers build an entire Honda Civic EP3 fuel return system, and we decided to write a complete guide to help you!

There are multiple reasons for upgrading to a fuel return system, but the main one is that the fuel flow becomes restricted when getting to around the 350-400bhp mark.

In this article, we'll go over the steps you need to take to build and install a Honda Civic EP3 fuel return system.

A fuel return system helps maintain a consistent fuel flow to the engine, improving performance and fuel efficiency in boosted applications. 

The fuel feed line and OEM fuel pressure regulator become problematic when going for much more power than stock.

You have to build a return into the system to flow more fuel and make more power. Overall, having a fuel return system is essential for boosted applications of the K20 in an EP3 or DC5.

Why do I need an Ep3 fuel return system?

Last week, we had a customer get to the dyno after spending thousands on a new turbo setup to realise that he didn't have enough fuel to make the power he was after. Unfortunately, he has to book another dyno session.

The limited power was because the stock Honda Ep3/Dc5 fuel system runs on a return-less system, meaning that a single fuel line goes to the stock fuel rail.

The tank's stock fuel pressure regulator is also non-adjustable, making it harder to supply the fuel needed in boosted applications.

When doing a supercharger or turbo conversion setup, it's essential to consider every variable, not just the shiny things like turbochargers and wastegates. (we've all been there!)

Boosted cars are not the same as running a naturally aspirated car, as you need to increase fuel pressure and supply to match the pressure shown at the intake manifold.

The more boost you run through the engine, the more fuel you need. It's as simple as that!

As you increase boost pressure, the fuel pressure generally goes down, which means the injectors will get less flow and need to stay open longer.

The injectors will now be running at higher duty, so the best way to counter this is to run a larger fuel pump, injectors, and, more importantly, a complete fuel return system to be able to regulate the fuel pressure with an adjustable regulator.

A fuel return system is the fix to most of these problems, as you will gain much more fuel flow with a larger fuel pump and fuel lines. With a 1:1 adjustable fuel pressure regulator, you should always see more fuel on the rail than on the stock one.

A vacuum hose will always be connected to the aftermarket fuel pressure regulator, increasing the fuel flow with intake manifold pressure, and anything left over will be returned to the fuel tank.

How do I choose which parts I need?

So, a few variables align with the power and build specification you're going for.

The first main one to consider when building an Ep3 fuel system would be the type of fuel you're using. A rubber-based AN hose would be a good option for using standard pump fuel.

You'll have to use a PTFE hose for anything more aggressive, such as race fuel or E85.

We have written an ultimate guide to AN fittings if you need to learn about the differences.

Since writing this article we have now also added guides for how to install PTFE fittings and how to install AN fittings to braided hose, which are worth checking out.

Before we move on, one important thing to note is that if you're running the fuel line through the car, you must use the PTFE line.

This is because PTFE is non-porous, so it will not let any fuel vapour inside the vehicle.

The next thing to consider would be the budget. In reality, this isn't something you can do with a budget of £50, but it is doable with around £350-£800 if you choose the correct parts.

The most expensive parts would be the injectors, fuel rail, fuel pump and fuel pressure regulator.

Now you've chosen the fuel type you want to use and budget; you can move on to choosing the parts you'd like to use for this swap.

What do you need to build an Ep3 fuel return system?

When building a fuel return system, you must decide on several parts. First, you must choose the size of the k20 injectors and fuel pressure regulator.

Currently, the most common turbo k20 injector size is 1000cc, as it can usually handle up to around 500bhp on a K20 at approximately 80-85% injector duty on pump fuel, which is considered a safe duty range.

To perfectly match your injectors to the application and horsepower you're going for, check out the fuel injector clinic injector size calculator, a great option for choosing injectors that match your specifications.

For brands of injectors, we either go with Grams Performance or Injector Dynamics, as we've had the most success with them in the past. They are flow-tested from the factory and have an incredibly low failure rate.

We often look towards either AEM Electronics or Hybrid Racing for the fuel pressure regulator, as both have a mega-low failure rate and are very good at perfectly holding the correct fuel pressure.

The last thing to choose would be fuel pump size, which again would depend on power rating. Still, we usually opt for the AEM 340lph fuel pump, which is incredibly reliable and will quite easily do 500bhp on a K-Series.

If you are using E85 or any more aggressive fuel, we recommend the AEM 340lph E85 fuel pump.

You will have already chosen a fuel pressure regulator, fuel pump and injectors. The next thing to decide on is what fuel you're using to choose the AN line.

If using standard pump fuel, we'd recommend using the nylon braided AN06 rubber line (or stainless if going for a silver theme) or the nylon braided AN06 PTFE hose for a more aggressive fuel.

You will need around 10-12m to do the entire system, so bear this in mind. This is only a rough guide of length; you should measure to ensure you're getting the correct amount of AN line and don't run out halfway through!

Next on the list would be to choose a fuel rail. Unfortunately, you cannot use the stock OEM fuel rail as you need more ports for a fuel return system.

Luckily, many aftermarket fuel rails already have AN thread to simplify this swap, and some offer a central feed or return if going for a tucked build.

Our go-to for this is usually the Hybrid Racing fuel rail, as they have a range of colours and fitment for the rails. They all include a centre port and are typically ORB08 and include adapters, which makes going up to an AN08 fuel line size very simple.

The last few bits you'd need would be fittings to either attach any of the above components or used in modifying the fuel pump hanger housing, which we will explain how to do later on in the guide.

Fuel Return System Parts Checklist

Before we go into how to install the entire system, you will need to make sure you have all of the parts to make this EP3 fuel return system work.

This is an essential list, but if you have any routing variations, you may need to swap out some of the parts or have extra fittings or different angles, etc.

This list is based upon a 500bhp system we built for a customer using pump fuel (braided rubber line). The parts used (such as fuel pump size, etc.) are down to the power you aim for.

Fuel Return Parts List

• Hybrid Racing dust black Ep3 fuel rail
• Hybrid Racing fuel pressure regulator
• Hybrid Racing fuel filter
• AEM 340lph In-tank fuel pump
• Grams 1000cc K-Series injectors
• 12m AN06 braided nylon rubber hose
• 1 x 90 degree AN06 bulkhead connector with AN06 nut (for the return to the tank)
• 1 x AN06 to 3/8" EFI push-on adapter (for the feed from the tank)
• 6 x AN06 straight fittings
• 1 x AN06 45 degree fitting
• 1 x AN06 90 degree fitting
• 1 x AN06 straight push fitting

Fuel Return Optional Parts

• Exoracing fuel pressure gauge (to fit to the fuel pressure regulator)
• P-Clips to hold the fuel line under the car to the chassis
• Haltech Flex fuel composition sensor if running e85
• Haltech flex fuel fittings AN06 to 3/8"
• If you're using E85 swap all hose and fittings out for the PTFE versions.
• AN06 braided hose dividers to keep the fuel lines together and tidy.

How to install a fuel return system

Modify the fuel pump housing

Before we modify the fuel pump housing, you'll need to remove the negative battery terminal to ensure there is no chance of sparking in the whole system.

Firstly, we must remove the fuel pump sender and modify it for the fuel feed and return. Start by removing the rear seats and undoing the screws on the cover plate to the fuel filter/sender unit.

Next, you'll need to push the an06 to 3/8" adapter onto the fuel pump outlet and drill a hole for the bulkhead connecter to go through, which will be the return from the fuel rail.

Use the AN06 push fitting on the inside of the bulkhead connected and run a line from this to the sender unit.

Once you've modified the fuel pump housing it should look something like the images below.

Next, swap out the fuel pump for the AEM 340lph and refit everything back into the fuel tank.

Now, remove all the old parts you aren't using, such as the fuel rail, the hard-line fuel line which runs back to the tank, and anything else in the fuel system that won't be used.

Install the new fuel system parts

The next part is always our favourite, fitting all the lovely new shiny parts!

Start by fitting the injectors to the Hybrid Racing EP3 fuel rail and installing the rail onto the engine. Make sure to use the supplied ORB08 to AN06 fittings at either end of the rail to prepare for the fuel lines later.

Find somewhere to mount the Hybrid Racing fuel pressure regulator (preferably onto the firewall) and screw in all of the adapters you will be using, making sure either the left or right port is the feed, the other port is blanked, and the bottom port is converted to AN06, which will be the return to the tank.

You must connect a vacuum line from the fuel pressure regulator to a vacuum source to ensure it can rise 1:1 with boost pressure.

The most efficient place for this would be on the intake manifold, but anywhere in the vacuum system should be fine if you cannot connect it here.

If you're using a fuel pressure gauge to monitor the fuel pressure, now is the time to install it onto the regulator.

As a side note, there is usually a 1/8"Npt hole on the fuel rail, which many people choose to install the fuel pressure gauge, but we always recommend not to install it here, as the engine vibrations can kill the gauges over time.

We've seen this happen multiple times, and many companies manufacturing the gauges now will not warranty the gauges if they have been mounted to a fuel rail.

You are always safer and will have a longer lifespan from the gauge to mount it to the fuel pressure regulator on the firewall where there is less vibration.

Connect the Fuel Lines

Now is the time to make up all AN06 braided lines to connect the entire system.

Before you decide to start making lines, please ensure you are confident in making the lines up yourself; otherwise, you will encounter leaks, which, as you already know, is incredibly dangerous.

If you need more confidence, please get a mechanic to install this system.

As a side note, to ensure you get the best quality finish, make up the fittings in a vice, using AN vice jaws and AN spanners to reduce the chance of marking or damaging the fittings.

Now it's time to make the lines! You will need to make all of these lines up:

• The line from the fuel pump housing to the fuel filter (this is usually mounted underneath the car)
• The line from the fuel filter to the fuel rail
• The fuel rail to the fuel pressure regulator
• The fuel pressure regulator back to the return port on the fuel pump housing.

Please refer to our fuel return diagram below if you need help determining where each line and fitting will go in this system.

Test your new Ep3 fuel return system

Now you've finally installed the entire system, it is time to check everything.

Please ensure everything you have installed is tight and secure, whether the fuel rail or any of the fittings, to ensure the smallest chance of a leak.

Once you're happy everything is tight, put the negative battery terminal back on and prepare to prime the system.

Next, pressurise the system by turning the key one turn on the ignition. This also checks that the fuel pump is working correctly.

Check the entire system for any fuel leaks, which you will either see or be able to smell.

If there are no leaks, you have just successfully installed your brand new Honda Civic ep3 fuel return system and can now adjust your fuel pressure accordingly and get ready for mapping!

FAQ

What is a fuel return system?

A fuel return system uses a fuel pressure regulator to change the fuel pressure based on a vacuum from the engine (generally from the intake manifold). It utilises a return to the fuel tank for any excess fuel not used by the injectors.

Can fuel pressure be increased on a stock regulator?

No, the factory Honda Civic Ep3 fuel pressure regulator is between 43 and 47 PSI, so you must run an aftermarket version if you would like to adjust the pressure.

Do I need to use an Ep3 fuel return system?

If you're going over the 400bhp mark, anything under this, you should be OK with the stock system.

Do I need to run the whole feed and return from the tank?

You can run the feed from the engine bay hard line located on the firewall if you would like, using an adapter, such as the Acuity AN06 to 1/4" EFI adapter. Still, you must run that line directly back to the fuel tank because there is no OEM return.

Which is better, a return or return-less system?

They have advantages, but you are always better off going for a returned system for higher horsepower, as you can adjust the fuel pressure to keep the injectors with the correct flow.

Should I run rubber or PTFE hose?

This depends on the application, but if you run the hoses through the car or use aggressive fuels such as E85, you will have to use PTFE, as the rubber hose can not handle either.

Using standard pump fuel, you will be fine on a suitable rubber-lined AN hose.

Do I need to use every brand you recommended?

No, you don't, but you must use at least some version of each product. The brands we've recommended are just the brands we have had the most success with in the past and the lowest failure rate.

Conclusion

In conclusion, if you want to get the most power from your Honda Civic Type R Ep3, and you're going for more power than 350-400bhp, then a fuel return system is worth the investment.

We've covered all the brands you'd need and a complete parts list to make this fuel system conversion as straightforward as possible.

Although it isn't the cheapest modification possible, it's needed at that power. Now, hopefully, you have gained enough knowledge to install it yourself!

Please don't attempt fuel system fitting or line-making in this guide if you need more knowledge. Get a professional to install it for you, as fuel systems are hazardous if not installed correctly.

If you need more help with anything mentioned in this article, please message us via our contact page, or if this guide has helped you, please leave us a message below!

Next you should head over to either our EP3 engine tuning guide, or the 6 best EP3 braking upgrades to get the most out of your brand new fuel system!