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Return vs “Returnless” Fuel Supplies - Conversion


kcbhiw
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All,  

 

I’m considering converting my car to a “returnless” style supply. The reason being, fewer hoses and bits under the hood, less fuel heat soak, and a small reduction in weight.  I’d be moving my filter and regulator to the rear next to the cell.  I already have an enclosed fuel cell, so isolating the fuel system components isn’t an issue. 
 

My big question is, has anyone had any vapor lock or hot re-start issues with their returnless system when coming off track(either converted or OE)?

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Neon is returnless OE, ran without issues for years. 

 

Takes longer to refire when you run car out of fuel. Holding open the Schrader valve to pump the air out helps. That is the largest practical shortcoming I have seen. 

 

When you run it that far out of fuel, it comes back on the back of a truck anyway. 

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No problems at all, it really is a much cleaner system, only a single -6 line from the back to the front. The only better system would be the fuel cell mounted in the passenger seat area with the pump, surge tank, and regulator mounted in front of the cell. Then you would only have 2 ft or so in the whole system.

 

pump.thumb.jpg.1ae7452db7c626d5668455e2d0970d7b.jpg

 

The only problem I had was something that no one else is likely to have. It was back when I was still running the GSL-SE system where the whole engine ran from 2 injectors firing together and positioned about an inch apart. At about 5000rpm the frequency of the injectors created a resonance in the tiny fuel rail, and shut off flow, if you could get it past the resonance point it would rev out to 9000 at full power with no problems. The solution was to install a few feet of rubber hose with a plug coming from the opposite end of the fuel rail.

 

 Since I went to the MS and a 4 injector S5 style system it has never been a problem, I don’t think a piston engine would never have a problem with more injectors and much higher volume fuel rails.

 

IMG_20151129_162937.jpg.4da76da5bd6a8625c8044eccd3c64ded.jpg

 

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Returnless is very convenient, I like our system and have not had issues. It looks very similar to the picture shown by MHR650. Also while you are doing returnless, getting rid of the vacuum reference (if your car has it) removes another level of complication. 

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I've often wondered about how this works with fuel pressure. 

 

NA Miata is a return type system, regulator at the end of the rail that bleeds off excess pressure.

 

NB (at least NB2) is a no-return system.  How would the NA fuel system cope with a non-return rail?  Would it have issues maintaining the proper AFR as the pressure in the rail is less accurate?  I know that bumping the rail pressure will allow an NA to run richer (assume it would work to make it leaner if there was less pressure). 

 

If someone has information on this I would be curious.

 

Edit - FWIW the NA tends to be a sharper cut off when it skips for lack of fuel.  The NB is a softer skip.

Edited by MMiskoe
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22 hours ago, turbogrill said:

NC is return less, no issues. High HP NCs change to return style to get more even pressure over the injectors I think, probably not a problem for us.

 

 

Those high HP cars are probably turbo cars, so they need to reference fuel pressure to boost pressure. Using a return style regulator just makes that easier to do, plus if they are really making a lot of power, they may be beyond what an in-tank pump can supply.

 

12 hours ago, MMiskoe said:

I've often wondered about how this works with fuel pressure. 

 

NA Miata is a return type system, regulator at the end of the rail that bleeds off excess pressure.

 

NB (at least NB2) is a no-return system.  How would the NA fuel system cope with a non-return rail?  Would it have issues maintaining the proper AFR as the pressure in the rail is less accurate?  I know that bumping the rail pressure will allow an NA to run richer (assume it would work to make it leaner if there was less pressure). 

 

If someone has information on this I would be curious.

 

Edit - FWIW the NA tends to be a sharper cut off when it skips for lack of fuel.  The NB is a softer skip.

 

I monitored my fuel rail pressure, and it was rock solid, exactly where I set the regulator in all conditions, even though the regulator was all the way at the back of the car.

 

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One issue I've run in to on my (return-less) NC is fuel pressure fluctuation. When I installed a Radium fuel rail for its fuel pressure port, I logged at 500 Hz just for the lulz, and saw this on a free rev:

 

170013219_10159409000502340_6442660193444481792_n.jpg?_nc_cat=109&ccb=1-5&_nc_sid=b9115d&_nc_ohc=_PcHSZrULCMAX8MTsbD&_nc_ht=scontent-atl3-2.xx&oh=626d427a2e2ea92440a5a8dad6e9dcf8&oe=61A877D1

So I installed a Radium fuel pressure damper, which seemed to fix the issue:

 

No photo description available.

 

Curiously, Radium says one thing manufacturers do to avoid these oscillations is use "rectangular cross-section fuel rails with a carefully tuned width and height", and the stock rail was rectangular. Maybe this wouldn't occur with the factory rail? Hard to say since it didn't have a fuel pressure port. It's very thin and brazed together.

 

The rest of the fuel system is stock.

Edited by Grant
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On 10/27/2021 at 9:13 AM, mhr650 said:

I monitored my fuel rail pressure, and it was rock solid, exactly where I set the regulator in all conditions, even though the regulator was all the way at the back of the car.

What frequency did you log at?

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7 hours ago, Grant said:

What frequency did you log at?

 

I was only able to log at 10hz back then, so no high frequency logging.

 

Not surprised that you found a benefit using a damper, after I had the experience of setting the car on fire because of standing waves in the fuel rail I was extra cautious when I redid the system to use MS and a 4 injector S5 intake. Those black parts which look like regulators are an OEM Hyundai fuel pressure damper. They are nice parts, just a simple 3/8 NPT thread so you can fit them in pretty much any fuel system. You can see I did a bit of belt and suspenders since I was coming off of a bad experience. I connected the ends of the 2 rails plus added a damper to both rails, probably overkill but I wanted to be sure I didn’t repeat the problem.

 

 

rail1.jpg

Edited by mhr650
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10 hours ago, Grant said:

 

Curiously, Radium says one thing manufacturers do to avoid these oscillations is use "rectangular cross-section fuel rails with a carefully tuned width and height", and the stock rail was rectangular. Maybe this wouldn't occur with the factory rail? Hard to say since it didn't have a fuel pressure port. It's very thin and brazed together.

 

The rest of the fuel system is stock.

 

 

I'll be collecting a fuel rail from a mid-2000s Focus this week to install on my 2.5 MZR.  These were equipped with an OEM pressure (and temperature) sensor, but the rail is otherwise dimensionally the same as the rest of the MZR rails.  I'll log the pressure after its installed and will report back.

 

image.png.43912f99ee803ddd69c8cbd9e8035f31.png

Edited by kcbhiw
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38 minutes ago, kcbhiw said:

 

 

I'll be collecting a fuel rail from a mid-2000s Focus this week to install on my 2.5 MZR.  These were equipped with an OEM pressure (and temperature) sensor, but the rail is otherwise dimensionally the same as the rest of the MZR rails.  I'll log the pressure after its installed and will report back.

 

image.png.43912f99ee803ddd69c8cbd9e8035f31.png

 

Interesting, I like that. I was planning to log both fuel pressure and temperature anyway, if I can do it with a nice integrated OEM sensor that is a bonus. We wouldn’t need to use the hose barb since we are not using the sensor to regulate fuel pressure with PWM and wouldn’t really care about vacuum referencing fuel pressure anyway.

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  • 2 weeks later...

Post returnless conversion, I took a datalog of a quick throttle jab, similar to test from @Grant above.  I seem to get pulses of about +/- 4PSI on fast throttle transients. Steady state seems pretty calm. 

Fpress.png

Edited by kcbhiw
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2 hours ago, kcbhiw said:

Post returnless conversion, I took a datalog of a quick throttle jab, similar to test from @Grant above.  I seem to get pulses of about +/- 4PSI on fast throttle transients. Steady state seems pretty calm. 

Cool, that's a lot better than my +/- 15 psi with a circular Radium rail. I guess Ford thought this was good enough.

Edited by Grant
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26 minutes ago, TiredBirds said:

Didn't know you could run FI w/o a return. That is a lot of pressure. We run a return (stock) mechanical pump/carb'd. No issues. I suspect we could do away with it. 

"returnless" is misnomer... it is a returning system, but the return happens back at the fuel pressure regulator itself, not from the rail. In our case, the fuel pump and fuel pressure regulator and cell are in the trunk. The pump puts out some unknown maximum pressure, say, 100 psi to the fuel pressure regulator. 60 psi worth of fuel is pushed to the fuel rail and doesn't return. The excess fuel bleeds right from the regulator back to the cell on a very short return loop.

Edited by enginerd
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17 hours ago, enginerd said:

"returnless" is misnomer... it is a returning system, but the return happens back at the fuel pressure regulator itself, not from the rail. In our case, the fuel pump and fuel pressure regulator and cell are in the trunk. The pump puts out some unknown maximum pressure, say, 100 psi to the fuel pressure regulator. 60 psi worth of fuel is pushed to the fuel rail and doesn't return. The excess fuel bleeds right from the regulator back to the cell on a very short return loop.

ahhhh yeah our return is at the mech-pump. 

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On 11/15/2021 at 4:43 PM, enginerd said:

"returnless" is misnomer... it is a returning system, but the return happens back at the fuel pressure regulator itself, not from the rail. In our case, the fuel pump and fuel pressure regulator and cell are in the trunk. The pump puts out some unknown maximum pressure, say, 100 psi to the fuel pressure regulator. 60 psi worth of fuel is pushed to the fuel rail and doesn't return. The excess fuel bleeds right from the regulator back to the cell on a very short return loop.

 

My understanding is that lots of modern cars run a returnless fuel system that is truly returnless - they use a pressure sensor in the rail and a PWM pump to maintain the pressure at whatever the specification is.  The duratec 30 we're swapping in only came returnless, but we're adapting the fuel rail to have a return and a real regulator.

 

I don't think our microsquirt can handle a PWM pump but the MS3Pro can.  Not sure about other megasquirts.

 

Your short return loop idea is nice.  I hadn't thought of that.  Did you run a vacuum reference from the engine back to the regulator?

 

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6 minutes ago, krispykritter said:

 

My understanding is that lots of modern cars run a returnless fuel system that is truly returnless - they use a pressure sensor in the rail and a PWM pump to maintain the pressure at whatever the specification is.  The duratec 30 we're swapping in only came returnless, but we're adapting the fuel rail to have a return and a real regulator.

 

I don't think our microsquirt can handle a PWM pump but the MS3Pro can.  Not sure about other megasquirts.

 

Your short return loop idea is nice.  I hadn't thought of that.  Did you run a vacuum reference from the engine back to the regulator?

 

 

A truly regulator-less system is still quite rare.  I actually can't think of a single normal person car using such a setup.

 

Many return less cars PWM the pump in addition to a regulator mounted in the fuel tank.  The computer runs the pump less at idle and low load to conserve energy.  But there's still a mechanical regulator built into the fuel pump sending unit.

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33 minutes ago, Ian said:

 

A truly regulator-less system is still quite rare.  I actually can't think of a single normal person car using such a setup.

 

Many return less cars PWM the pump in addition to a regulator mounted in the fuel tank.  The computer runs the pump less at idle and low load to conserve energy.  But there's still a mechanical regulator built into the fuel pump sending unit.

 

Today I learned.  Thanks!

 

And I think we've talked ourselves into going with a returnless-style fuel system with the regulator in the trunk.  Thanks for the commentary.

Edited by krispykritter
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1 hour ago, krispykritter said:

 

My understanding is that lots of modern cars run a returnless fuel system that is truly returnless - they use a pressure sensor in the rail and a PWM pump to maintain the pressure at whatever the specification is.  The duratec 30 we're swapping in only came returnless, but we're adapting the fuel rail to have a return and a real regulator.

 

I don't think our microsquirt can handle a PWM pump but the MS3Pro can.  Not sure about other megasquirts.

 

Your short return loop idea is nice.  I hadn't thought of that.  Did you run a vacuum reference from the engine back to the regulator?

 

 

As long as you are naturally aspirated you don’t need to bother with a vacuum reference.

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44 minutes ago, mhr650 said:

 

As long as you are naturally aspirated you don’t need to bother with a vacuum reference.

 

I was googling that, and apparently it's definitely recommended by the megasquirt tech guys.  I guess the fueling algorithm has the reference built into the equation.  I'm sure you can tune around it though.  We've already got a return line plumbed from engine bay to trunk so it's easy enough to repurpose that into a vacuum line.

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