I'm running the same as JerseyMini, with no issues on a D16Z6 and a JDM D15B setup.  Sounds like the pump or regulator is the issue. I also run wiring to the pump  using a relay direct to battery (both located in the trunk along with the filters)  through a fuse, using the pump wiring from the ECU to trigger the relay.

Just wondering if the voltage supply line to the pump could be undersized, not letting enough current thru for the pump to be fully operating? Also check that the pump has a very good/clean ground connection.

Wow,8an is huge.

Factory EG honda fuel feed lines are only 5/16th and people have made well into the 600whp range with them.

I'm running dash 8 feed and dash 6 return on my B18 swapped mini.

I am not sure what year or engine size is at issue here, but Honda started running single feed fuel line in most 2003 up models and has the pressure regulator in the tank mounted to the fuel pump assy which means that any excess fuel is dumped right back into the tank, so there is no need for a return. If the fuel rail does not have a regulator fitted to maintain pressure in the rail  example an aftermarket rail, one must be added to maintain pressure at the injectors on the return to the tank. Hope this helps.

Cheers
Minsuki.

Im running a 5/16 fuel Feed and a 1/4 inch return(factory mini feed as the return). Walbro 255lph external pump.Ive ran a cheap airtex e2000 pump from autozone also and it worked great.

This is on a Turbo D16. Never had any issues this way.

I

The filters have been disassembled, and checked.  The Mini has 6 miles on it since the conversion.

I didn’t mean to imply that the pump was flowing everything it could.  It’s slowly starving for fuel at idle.   After eliminating all other factors in the fuel system, I’m 99% sure that the fuel hose diameter both before, and after the pump is wrong.  On a K-Jet car, this exact fuel pump is used to get the system to an operating pressure of about 70psi.  Anything less than 60 psi, and the injectors won’t fire.  This is on most old Mercedes, Porsches, VWs, etc.  So, I know that this fuel pump is capable of powering a Mercedes v8, or a 911, and that I’ve eliminated the fuel tank, and the serviceable fuel filters have been checked, and there isn’t enough flow to get fuel out of the return line.  All of this taken into consideration, I’m left with what I know of those systems.  Every last one of them has a different sized supply, and pressure line, most have accumulators before the pump as well.  

     Can any of you with a Vtec Mini tell me what size fuel lines you have in the car?  If anybody says that they’re running 3/8” on both sides, I can possibly eliminate that from my troubleshooting.  If not, what do I need?  I think it’s going to be 7/16” supply, and a 5/16” pressure line, but that would mean that I have to completely gut and redo the fuel system in this car, from the sending unit to the regulator.  If that’s the solution, fine.  Before I go to that extreme, I just want to know if anybody’s gotten this setup to work.  It’s possible I need a different fuel pump, one that’s designed to build less pressure.  

     I don’t want to throw my customer’s money at the car, unless I have something to go on.  What fuel pumps are Vtec guys running with what sized fuel lines?

Thanks,
Reid.  

If the pump is pulling fuel at full rate, and nothing's being returned to the tank - where's the fuel going? I do not believe a K-series Honda can consume even half the fuel delivery of any automotive fuel pump at idle. If the pump is really exceeding the flow of the feed line it's got to be going somewhere.

And unless the fittings flare out to a line of greater diameter on the exit side of the pump, the pump will be the bottleneck point of the system anyway. But bottom line, that's the question I have - where's all that fuel going if the pump is delivering all the fuel it's capable of? The flow difference between 7/16 and 3/8 isn't going to be noticeable at idle. It's not reducing flow by 90%.

The fact that nothing is coming back from the return line makes me suspect that the pump isn't delivering anything close to its rated capacity - be that due to current supply issues, a defective pump, or a clogged/collapsing fuel line - those would be my suspects.

I chased an issue similiar to this and swore it wasn't the filters,and it was. Lol just reread and seen you eliminated the tank. Could also be a voltage issue if the wire is too thin and not adequate.

Sounds like a vent issue to me...What kind of vent do you have on the tank?

Also,visually looking at a fuel filter you cant tell if the filter is "dirty" as a lot of the time they Gel up and you cant even tell. Take the filters off and try lightly blowing through them.

3/8 line is pretty big and should be way more than enough.

Thanks for your reply,
     It’s dropping at idle, and no fuel is making it back out of the return line.  I can hear the pump start to cavitate at around 25 psi, so I shut it off there.  Don’t worry, I’m not driving a vtec swapped, and slammed mini clubman with open jugs of gas in it.  This is a bench test only.  If the regulator is bad, then fuel would be bypassing it to the return line.  That’s not happening here.  Nor is there black soot out of the exhaust, so I can’t blame an injector.  Which brings me back to the size differential between the supply and pressure lines.  The pump cavitation leads me to believe that it’s running out of fuel to pressurize.  

A (hypothetically) too-small line won't reduce pressure. It may reduce flow, but what flows out likely will be at a higher pressure than from a larger line (i.e. behaves just like a restriction.)

So when running, for the pressure to fall, either the engine is consuming more fuel than the pump can supply. What's the rating of the pump? Is the pump sized for a smaller engine? Does the pressure drop only when operated under load, or does it drop just idling?

If it dropped just idling, I would look elsewhere first - maybe a defective pressure regulator with a small leak that seems to hold pressure statically but can't keep up under load. If it dropped only under use, I'd still suspect the regulator first unless that pump is sized for a much lower HP engine.

Now, if the pressure drops under heavy load, then it could be a case of the supply line being undersized and unable to bring in enough fuel to keep the post-pump side pressurized. It's hard to believe though that a healthy fuel pump couldn't maintain pressure at idle or low load operation.

A leak in the supply line running to the pump (immersed portion if an in-tank pump, or the pickup part of the line for an external pump) can also cripple flow (and thus pressure under demand) because even if the pickup line is immersed, a leak can mess with the intake flow. Mainly, the intake line might be collapsing from suction if there's a hole in it. I guess if you're driving it around with the lines in jugs though that's not it (pretty risky business doing that though.)

I’ve got a customer’s classic mini with a K swap in my shop.  It’s an incomplete build, and I’m sorting it out for him.  It’s running out of fuel pressure, and lean bogging to the point of undrivability.  I took a look under, and he’s got a Bosch CIS fuel pump with the necessary filters in place.  Filters, tank, sock are all clean.  Pressure regulator is hooked up and functional.  I just ran the supply and return lines in and out of different fuel jugs.  Same problem, eliminates issues with the tank.  Then I noticed that all of the fuel lines, supply, pressure, and return are 3/8”.  All of my CIS cars (Volvos) run a larger supply to the pump for volume (7/16), and a smaller pressure line.  So I think I found the problem. But my question is what size does each need to be for this set up? 7/16 supply, and 3/8 pressure, or 5/16 pressure? I don’t think that the injectors are more than stock, nor is the engine. Shouldn’t be a very meaty set up. Can anyone help?  

P.S.  Changing the 3/8 supply feed in the tank to a bigger one will be heinous.  Could the 3/8 work with a 5/16 pressure line?
          I’ve also tested different fuel pumps, all act exactly the same.  Start at full pressure, and slowly lose it while running.

Thanks,
Reid