returnless fuel lines - I just want to understand it.

[barryogen]

I understand that cars used to use a constant pressure returnless fuel line, where the ecu(?) would essencially change fuel pressure by choking the return line, thus increasing the pressure in the fuel line.

Now, I understand that newer cars use a returnless fuel line, but do they do this by having a pump giving a varying pressure or what?

And if so, what would a change to bigger injectors do, just make it run rich?

If engine 101 is what I need, just point me in the right direction, as I think I'm going to need it.

Thanks in advance.

[Malcolm]

on a normal system, you have a pressure regulator, which is an entirely mechanical device, choking down the fuel return to pressurise the system (not really tampered with by the ECU, except sometimes they use solenoids to slightly alter it)

I'm guessing that the returnless systems have the pressure regular down near the fuel pump, and so you have a fuel "loop" that goes:
[tank] - [pump] - [pressurised line that is tee'd off] - [pressure regulator] - [return line back to tank]

now the line that tee's off the pressurised line would run to the engine bay, and viola - returnless fuel rail.

that's how I would think it would work anyway

[barryogen]

I'm guessing that the returnless systems have the pressure regular down near the fuel pump, and so you have a fuel "loop" that goes:
[tank] - [pump] - [pressurised line that is tee'd off] - [pressure regulator] - [return line back to tank]

now the line that tee's off the pressurised line would run to the engine bay, and viola - returnless fuel rail.

that's how I would think it would work anyway

thank you for that, you pretty much answered my question, except for a few minor details, and this site
http://www.findarticles.com/p/articles/mi_qa3828/is_200410/ai_n9426858
sorted that out.

Returnless Fuel Systems
Motor, Oct 2004 by Seyfert, Karl

To ensure adequate fuel pressure and volume under constantly changing operating conditions, conventional fuel systems always pump more fuel to the injectors than is ultimately needed. That means one molecule of fuel might make as many as 30 trips to the engine via the fuel rail before it finally passes through an injector and is converted to energy. Each trip adds heat to the fuel, which is returned to the fuel tank. In-tank fuel temperatures can exceed 160°F on a hot summer day-a prime breeding ground for fuel evaporation. Even if it's properly contained, vaporized fuel can contribute to a variety of driveability problems. Remember carburetor vapor lock?

To combat these problems, several vehicle manufacturers have introduced fuel systems that reduce the number of tank-to-engine trips to just one. Because these systems do not have a return line to return the unused fuel from the engine to the tank, they have been dubbed refumZeas fuel systems. This is something of a misnomer, as the unused fuel really i; returned to the tank. It just doesn't have quite such a long return trip to make. These systems were introduced in the mid-'90s, and their use is rapidly expanding.

On returnless systems, fuel is picked up via the fuel screen sock at the bottom of the tank, then routed to the fuel pump. The pump supplies the needed fuel pressure and volume to the engine and the excess is directed back into the tank after passing through a pressure regulator. The regulator lacks the vacuum connection to the engine that we're accustomed to seeing on conventional pressure regulators, so its job is to maintain a steady pressure independent of any changes in engine operating conditions. To make sure the engine always receives just the right amount of fuel for current conditions, the PCM makes rapid changes in injector pulse width instead. On some newer fuel systems, a pressure sensor keeps the PCM informed of system fuel pressure. The PCM responds by modifying the pulse width to the fuel pump power supply, adjusting system pressure and volume on the fly. These newer systems completely eliminate the need for a separate pressure regulator.

One advantage of the older returntype fuel systems was the constant filtering of the fuel they provided. Each time the fuel made a trip to the engine, it had to pass through the fuel filter. The filter trapped tiny particles of dirt or debris that may have found their way into the system. This cut down on component wear and service was relatively simple because the filter was usually in an easily accessible location outside the fuel tank.

Returnless fuel systems also have fuel filters, but where those filters are placed can have a big effect on the longevity of the system, as well as its ease of service and repair. The filter can be placed in any of three different locations. The first is the conventional location outside the tank. While this is the easiest to service, it also means that any unused fue] that's returned to the tank is never iiltered until it makes its first and only trip to the engine. So if it contains any contamination, the same junk will make repeated trips through the pump and back into the tank. A load of rusty fuel could pass repeatedly through the fuel pump, grinding the rust particles into increasingly smaller particles and making short work of the pump itself.

Placing the filter in front of the pump protects the pump from contamination, but creates other problems. The most obvious drawback is that the filter is now in the tank, so replacing it is a major deal. A filter that's become clogged with debris means the pump now has to suck extra hard just to get the fuel it needs. This causes low fuel pressure, fuel boiling and pump cavitation. So-called lifetime filters are supposed to alleviate all of these drawbacks.

The last option is to place the filter after the pressure regulator, before the unused fuel is returned to the tank. This allows the unused fuel to be filtered repeatedly, until it's finally used. A restricted fuel filter is less likely to have an adverse effect on the fuel pump, and the filter can be placed in a location on top of the tank that is easily accessible for replacement.

Fuel system cleanliness is important on any system, but never more so than on a retumless system. Any dirt left behind will quickly damage any new components you install.

so there are both good and bad sides to it... the worst bit of it will be that to re-tune if I add boost to my car will be somewhat of a PITA.

[Malcolm]

interesting indeed. I wonder if you could replace the regulator with a conventional one, and run a vacuum line all the way to the fuel tank? that would make it better for boosted applications

[barryogen]

interesting indeed. I wonder if you could replace the regulator with a conventional one, and run a vacuum line all the way to the fuel tank? that would make it better for boosted applications

well the eventual plan is to do this...
http://www.sportcompactcarweb.com/projectcars/0201scc_projmatrix/

The matrix AFAICT is a latest Caldina import shape with the 2zzge engine... they add boost, but in the end kill it, I'd like to do the same, minus the killing bit.

ooh, look at that sweet set of headers....


gotta love the air going in the front and exhaust out the back of the engine... well, atleast I do.

[Malcolm]

good for keeping your feet warm in the winter I suppose

[barryogen]

good for keeping your feet warm in the winter I suppose

indeed... after the recent blat to Timaru(for the drags) and back(heavier foot on the way back), I noticed that the left of the drivers foot well was rather warm, and you have just explained why... don't know why I hadn't thought of that before now.

heh, thats actually quite hilarious... when boost is added I'll have to make some additional heat shields and maybe some ducting to keep it cooler.

something else to keep in mind.

[Ako]

Exhaust = Keep it hot, heat wrap the bugger and by rights you should get gains. DONT try and cool it down, its counter - productive.


p.s - the manifold on the front with the little sucky / blowy type thingy on it is 10X cooler than the one at the back

[barryogen]

Exhaust = Keep it hot, heat wrap the bugger and by rights you should get gains. DONT try and cool it down, its counter - productive.

sorry, I should have clarified... when I said may need to add some ducting, I meant to cool the foot well, when I said it was getting hot, it was literally hot, not just warm, although the car was driven "very hard" with "spirited" driving on the way home, so only on track should it get like that.

p.s - the manifold on the front with the little sucky / blowy type thingy on it is 10X cooler than the one at the back

hell yeah, that is the eventual plan, this company made one to fit in the original manifold spacing so no modifying of the firewall was needed, this I see as a vary good thing as it would still look almost stock under the bonnet... barring the piping for the IC, but I may try to stealth that too.

[CozmoNz]

your car also has no heatshields on it remember barry, since u have teh trd items.

i think a heatshield, some heat wrap (see hrt's headers), and maybe even a sleeping bag for the turbo should keep everything in order.

hot feet eh? never heard of aircon?

[barryogen]

your car also has no heatshields on it remember barry, since u have teh trd items.

/me forgot
might do some welding... it felt "plastic melt hot" on the metal, paint looks almost scorched under the car.

i think a heatshield, some heat wrap (see hrt's headers), and maybe even a sleeping bag for the turbo should keep everything in order.

thats the idea... but having no turbo at the moment there is little point in bothering with it.

hot feet eh? never heard of aircon?

The gas milage was already pretty bad due to the "spirited" driving... I was hesitant to make it any worse.
Ask the guy who drives the older(late 80s early 90s?) black SC'd levin/trueno/whatever... I think he noticed when a few friends and I went passed.

[Mr Revhead]

im pretty sure the matrix is corolla based.....

the TRD exhaust still allows keeping the stock heat sheilds.....

[TRD Man]

im pretty sure the matrix is corolla based.....

That's correct.

[barryogen]

im pretty sure the matrix is corolla based.....

That's correct.

been trying to figure it out... either way, it is a sexy car... well, kinda.... much like mine.

[rolla_fxgt]

Yeah what speed were u doing just north of oamaru there dude? When the laurel with the huge front mount, the gtt caldina & u passed us?

I was doing about 120, so i guess u must of been doing closer to the 160 mark if not faster.

[barryogen]

Yeah what speed were u doing just north of oamaru there dude? When the laurel with the huge front mount, the gtt caldina & u passed us?

I was doing about 120, so i guess u must of been doing closer to the 160 mark if not faster.

no idea sorry but I'm guessing that you're right... we had a bit of an advantage traffic wise, a couple of RTs and some police scanners, the GTT had most of the gear, I just had a hand held RT, as did the Laurel(RB26 engine swap I think).

It was quite interesting to note that the GTT couldn't pull away from me(I couldn't pass him though), but the laurel would catch easily once we hit ~160...

not overly keen on doing that again, atleast not on the road, I'll leave the speeding to the track.

[CozmoNz]

Just wait until its turbo dave . was that laurel a dark purple colour?

[Alex B]

RB20DET accualy.

[barryogen]

RB20DET accualy.

Don't think that the laurel was purple, although the colour of cars never really sticks out to me.

RB20DET it is indeed, ran into them over the weekend, it's still not running right, but if you saw the rangi job that they've done of some of the work under the hood, you wouldn't question why.