Hi

Today I had the car to a position in my project where i could turn the ignition on and see if the returnline and relay control of the pump was working. The good news is the pump starts and runs just as it used to when turning the key. (maybe 2-3 seconds)

However, there is a problem.
When I installed the returnline I also installed a FPR. Now I can

 

Bump

 

Fuel pressure sensor, monitored by the ECU. The ECU varies voltage to the pump to maintain fuel pressure at the level that it wants.

 

Oh, how do I get around this then?

I mean to get the system to work like a normal fuel system with returnline.
I have the hondata kpro btw, which I am yet to get used to and learn.

 

No clue. My only experience with returnless systems is on mustangs, and it taught me only enough to know that I hate them.

 

1. Remove the OEM FPR which is located in the OEM fuel tank.
2. Have a custom fuel rail made (if a manufacturer hasn't already done so).
3. Tap the OEM fuel tank for a -6AN fuel line which will be used for the return fuel line.
4. Get an aftermarket FPR.
5. Run the OEM fuel feed line to the aftermarket FPR.
6. Run a fuel feed line from the FPR to the custom fuel rail.
7. Run the return fuel line from the fuel rail back to the OEM tank.
8. Use a Walbro 255 (or a Full-Blown double pumper setup if using E-85).
9. Use 1000cc injectors (or 1250cc injectors if using E-85).

If you really wanted to you could replace the OEM fuel feed line with a custom -8AN fuel line. If you do this up front you won't have to worry about the fuel lines ever again.

That is quoted from 2QYK4U. thats the advice he gave me. you can pm him or maybe he'll chime in here. he did the conversion too so he might be able to answer ur questions

 

1. Remove the OEM FPR which is located in the OEM fuel tank.
1. ??? Where is that FPR? I have had the tank insert out and could not see any FPR?? Here is the best pic I have of my tankinsert that i modified.


2. Have a custom fuel rail made (if a manufacturer hasn't already done so).
2. I did modify my oem fuelrail and welded return couplers on it.


3. Tap the OEM fuel tank for a -6AN fuel line which will be used for the return fuel line.
3. The returnline is installed and tested

4. Get an aftermarket FPR.
4. Got it. It is installed and working. In this pic you can see the FPR aswell as the returnlines i put arrows on.


5. Run the OEM fuel feed line to the aftermarket FPR.
5. Running the feedline to the FPR isnt what is usually done. The Feedline goes to the rail and the returnline goes to the FPR. It is in the rail you want the pressure regulated after all.

6. Run a fuel feed line from the FPR to the custom fuel rail.
6. Same as 5.

7. Run the return fuel line from the fuel rail back to the OEM tank.
7. Returnline is installed and working.

8. Use a Walbro 255 (or a Full-Blown double pumper setup if using E-85).
8. I am using a rewired walbro 255. Separate 11gauge cords from the battery with a relay controlled by the stock pump circuit.

9. Use 1000cc injectors (or 1250cc injectors if using E-85).
9. ID 1000s are installed, however I am not going to start until I get the fuelsystem to work as I want.

 

You're going to need to pull that tank insert out again. There's a regulator in it somewhere.

I'm trying to find info about the returnless system in the S2000 to help you out, but not having luck with finding anything that is specific to the S2000. At least I'm learning some things though. For example, they don't all use pulsewidth modulation to control fuel pump speed the way Ford does(thank god), so what I posted earlier may not apply to the S2000.

Everything I can find suggests that there's usually a FPR molded into that plastic tank insert that the pump is mounted in. Most likely with passages molded into the plastic to dump the return fuel out the bottom and back into the tank. If you can find an outlet hole in that insert and plug it, then your return system should work the way you want it to. You'll want to make sure that it's plugged very securely, because if it comes loose at high load you could be looking at catastrophic detonation...

 

How is the fuelpump controlled in the earlier yearmodels with the stock returnsystem? Is the pump just running a set speed all the time and the FPR makes sure the car gets the pressure and fuel it needs?

How about this returnless system? Since there are only 4 cords to the insert (2 for the pump and 2 for the fuel level indicator), I take the FPR has to be pure mechanical, and thus have no relation with the ECU. Thanks for the tip about a hole, it has to be that way.

 

There is no fuel pump control with most return style fuel systems. Toyota changed fuel pump speed in the TT supras based on load, but I highly doubt honda did that in the S2k. Usually the pump just runs at 100% at all times, and the FPR controls the pressure to maintain a steady pressure differential across the injector, over a wide range of manifold pressures. Very simple, very effective. The returnless system in the S2k could run the fuel pump the same way, not all manufacturers vary fuel pump speed in a returnless system. I really hope honda doesn't, but I can't say for sure. I know Ford does, and it results in a nasty hesitation in my buddy's whipple'd cobra if you lift off the throttle when you shift. Very frustrating.

You're right about the FPR in the returnless system, it's going to be purely mechanical. It's set for a certain pressure and opens to release fuel to keep the pressure from getting higher than the pressure setting in the FPR. In a system like this, you get different pressure differentials across the injector depending on intake manifold pressure, and the injector duty cycle is adjusted in the ecu to compensate for that.

Switching to a return style system is going to mean you have hours and hours of tuning ahead of you, unless you've got a k-pro base map for a return style fuel system.