Fuel return line

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Juro
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Fuel return line

Postby Juro » Sat Jun 27, 2015 3:09 pm

Why is the fuel return line necessary? Seems this would cause fuel pressure in the fuel rail to fall and cause
the injectors to stop operating.



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Asylum
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Re: Fuel return line

Postby Asylum » Sat Jun 27, 2015 8:22 pm

Ya you are right genius!

Why bother with what GM engineers developed! What a bunch of drunkin' idiots they must have been!

The GM MPFI and later SFI (which is still MPFI after 2500 RPM) were some of the best systems developed at the time.

It's the need to provide sufficient fuel pressure to satisfy the injectors, and what isn't required is returned to the tank.

And it helps cool the fuel and the pump.

The entire return fuel system acts like its own sort of fuel cooler.





OK that is a very over simplification of why, but consider the source of the question guys!

:beer:


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Re: Fuel return line

Postby Juro » Sat Jun 27, 2015 9:29 pm

My Plymouth Neon doesn't have a fuel return line.



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Re: Fuel return line

Postby Asylum » Sat Jun 27, 2015 9:58 pm

Juro wrote:My Plymouth Neon doesn't have a fuel return line.


And that is why Chrysler/Benz/Renault/Ferrari/Lamborgini/Fiat/Pappa Johns Pizza or whomever the hell owns them now still build junk as part of the effort to build North American disposable cars!

Actually it's a completely different fuel system.

However you continue to demonstrate that you know nothing about anything automotive.

:(


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Re: Fuel return line

Postby CorvetteBeretta » Sun Jun 28, 2015 12:40 am

Is this for real


Image

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ifixalot
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Re: Fuel return line

Postby ifixalot » Sun Jun 28, 2015 10:04 am

I'm not entirely sure of the correct answer. Let me offer a theory of a couple possibilities,
if you didn't have a return line the air would be trapped in the system.
With the return line air gets purged out so fuel is at the injector ready to be injected to start the engine.
Also I think I read that fuel is also used to cool the fuel pump so you need a flow of fuel going through
it to keep it cool.
I don't know how they solve these problems in a car with no return line if it is fuel injected.
On my old 68 Camaro, it has no return line because the air gets purged out through the float valve in the carburetor.
And that fuel pump is mechanical and on the outside of the engine, it has no electric motor to get hot.
It has a built in pressure bypass to regulate the lower pressure to about 6 psi.
Where with fuel injection the pressure is higher at about 40 psi.
In some cars, pressure bleeds off after you shut the engine off, that pressure has to go somewhere
and goes back to the tank through the return line.
There maybe be more reasons but thats all I can think of for now.



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Re: Fuel return line

Postby Juro » Sun Jun 28, 2015 2:21 pm

Thanks, ifixalot. This forum is like a bees' hive.

The fuel pump is inside the fuel tank and is submerged in fuel to prevent overheating.
This is why people who habitually drive with the gauge indicating empty often need fuel pump replacements.
Keep it at least a quarter full!

That said, i suppose the return line drains directly onto the pump to cool it.



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Re: Fuel return line

Postby ifixalot » Mon Jun 29, 2015 11:03 am

I've heard that theory too but since fuel flows through the line, out and back into the tank,
I think the lines act like a radiator to cool the fuel as it passes through to the front and back of the car.
There is an armature inside the pump that gets hottest. Outside of the motor has permanent magnets
which don't get hot. So fuel needs to flow through to cool the armature. Just sitting in fuel, I don't think
would be the most efficient.
I never let my tank go under 1/4 tank anyway.
You never know when you'll have get out of town in a hurry!! lol
You can do a general internet search of the same subject and find more info
without the "commentary". I found more info posted at other message boards.




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