04-07-2021, 03:19 PM
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#1
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Registered User
Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Fuel supply and return which is which?
This is a bit of an embarrassing question that I could have answered myself if I still had the original engine in the car but does anyone know what is the fuel supply and what is the fuel return line? I shamelessly stole this photo off another thread so if its your photo thanks. 
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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04-07-2021, 03:23 PM
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#2
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Registered User
Join Date: Oct 2014
Location: California Central Coast
Posts: 1,476
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Can't answer from the pic, but the fuel filter is close by. Trace from there?
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04-07-2021, 05:19 PM
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#3
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Registered User
Join Date: Oct 2018
Location: North Cali
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I`m pretty sure the right one is the return line.
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04-08-2021, 02:35 AM
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#4
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Join Date: Dec 2013
Location: Dahlonega , Georgia
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I would think but don't know that the larger line ( blue arrow ) is the supply and the smaller is the return . Hopefully someone smarter than me  will chime in .
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2002 Boxster S Arctic Silver with black top with glass window and black leather interior. Jake Raby 3.6 SS ( the beast ) with IMS Solution. 996 GT3 front bumper , GT3 rocker covers and GT3TEK rear diffuser and Joe Toth composites rear ducktail spoiler .
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04-08-2021, 06:56 AM
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#5
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Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Man I should have made this a poll!
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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04-08-2021, 08:32 AM
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#6
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Join Date: Feb 2005
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The one with the blue arrow should be connected to the fuel pressure regulator on the injector rail, and should be the feed line on a 97.
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
Last edited by JFP in PA; 04-08-2021 at 08:35 AM.
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04-08-2021, 08:47 AM
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#7
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Registered User
Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Quote:
Originally Posted by JFP in PA
The one with the blue arrow should be connected to the fuel pressure regulator on the injector rail, and should be the feed line on a 97.
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The fuel pressure regulator is installed on the feed line on Porsches? How does that work? Now I'm really confused.
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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04-08-2021, 08:52 AM
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#8
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Join Date: Feb 2005
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Quote:
Originally Posted by truegearhead
The fuel pressure regulator is installed on the feed line on Porsches? How does that work? Now I'm really confused.
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On the early cars, it was a vacuum operated diaphragm device on the fuel rail, as in the diagram.
The early fuel system included a return fuel line and had a fuel rail mounted fuel pressure regulator. For 2002, there is no return fuel line and the fuel pressure regulator is mounted in the fuel tank.
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
Last edited by JFP in PA; 04-08-2021 at 08:57 AM.
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04-08-2021, 09:14 AM
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#9
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Join Date: Feb 2005
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OK, seems after checking the early service manual, I have the lines reversed: The fuel pressure regulator in on the return line. Sorry bout that......��
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
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04-08-2021, 09:14 AM
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#10
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Registered User
Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Quote:
Originally Posted by JFP in PA
On the early cars, it was a vacuum operated diaphragm device on the fuel rail, as in the diagram.
The early fuel system included a return fuel line and had a fuel rail mounted fuel pressure regulator. For 2002, there is no return fuel line and the fuel pressure regulator is mounted in the fuel tank. |
Right, but typically these regulators are installed after the rail to ensure they are maintaining rail pressure (unless I’m wrong). Do I have this backwards?
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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04-08-2021, 09:17 AM
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#11
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Registered User
Join Date: Feb 2005
Location: It's a kind of magic.....
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See my previous post; seems my memory is not as good as it once was, but the service manual's always is................
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
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04-08-2021, 10:26 AM
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#12
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Registered User
Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Quote:
Originally Posted by JFP in PA
See my previous post; seems my memory is not as good as it once was, but the service manual's always is................
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Great thanks! I really need to get one of those service manuals and stop abusing you guys. thanks for all the help.
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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04-08-2021, 10:37 AM
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#13
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Registered User
Join Date: Oct 2018
Location: North Cali
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I think the question was also wrong  So, just to clarify, the right one that runs from the regulator is the return line. The left one (red) is a vent line. The feed line is not pictured, it is on the other side of the rail and is coming up from the fuel filter on the right side of the car. At least on mine, which is a 99 Base.
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04-08-2021, 02:11 PM
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#14
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Registered User
Join Date: Jul 2011
Location: Richmond, VA (The Fan)
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Quote:
Originally Posted by Homeoboxter
I think the question was also wrong So, just to clarify, the right one that runs from the regulator is the return line. The left one (red) is a vent line. The feed line is not pictured, it is on the other side of the rail and is coming up from the fuel filter on the right side of the car. At least on mine, which is a 99 Base. |
Ha! What a rollercoaster. Join us next week for: What are these “coolant” lines?
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1997 Boxster 4.2L Audi V8 Bi-Turbo
2003 911 C2
NASA HPDE Instructor
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10-15-2021, 12:35 PM
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#15
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Registered User
Join Date: Sep 2015
Location: SW Ohio
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My fitting at the blue arrow is slightly wet/weeping. Does anyone know whether there is an o-ring in the disconnect fitting that can be replaced? Other options of repair? And my vote is that it (blue arrow) is the return line (98 base)
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10-15-2021, 04:53 PM
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#16
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Registered User
Join Date: Oct 2018
Location: North Cali
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Quote:
Originally Posted by gdotcvg
My fitting at the blue arrow is slightly wet/weeping. Does anyone know whether there is an o-ring in the disconnect fitting that can be replaced? Other options of repair? And my vote is that it (blue arrow) is the return line (98 base)
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Mine was leaking too, but not at the connector, but at the fuel rail, and it was leaking down on the back side of the line. If it leaks at the connector, it`s also possible that the line itself is scratched where the fitting slides onto.
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