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ej swap, what do vacuum lines REALLY do 4 me?


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6 replies to this topic

#1 tallwelder81

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Posted 18 August 2012 - 12:00 PM

i have seen lots of of successful, functioning ej'd brats who ditched all the vacuum lines or pcv lines or whatever they are, that go into the air intake tube.

my question is this:

does KEEPING them benefit me in any way?
does keeping SOME, but ditching any inconvenient ones serve any purpose, or is it black and white, all or nothing?

i want to do my intake straight back, up over the spare tire "shelf".

i wont have enough room to keep all the tubes, and i wont have enough room for both of those weird "sore thumbs" that dead end off the intake on the imprezas.

i was told that those sore thumb hang-offs are to smooth the incoming air flow. to kinda break up high-and-low pulses, so its just one somewhat steady and consistent breath of air.

#2 Fairtax4me

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Posted 18 August 2012 - 01:43 PM

The early EJ's didn't have any of that "sore thumb" deal on the intake, just a straight tube from the filter box to the TB.

But you do need to keep the Breather hoses that run from the valve covers to the intake tube. They don't have to hook into the same place, but without them you'll have all kinds of other fun problems to deal with, like oil seals blowing out, and sludge in the crankcase.

Actually I don't suppose you HAVE to have them, you could put those little breather filter dealies that you get cheap on the rice rocket isle at Autozone on the valve covers, but they'll probably just leak oil all over the place.
I'd rather have the hoses connected to the intake tube in some way.

PCV stuff has to be there, but that isn't going to be in the way of anything.

Certain vacuum lines you absolutely DO need. Others depend on what your ECU is looking for.
Fuel pressure regulator has to have a vacuum line. No if's ands or buts. Although that's the only one that I can think of that's absolutely necessary for the engine to run.

Are you going OBD1 or OBD2?

#3 WoodsWagon

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Posted 18 August 2012 - 11:49 PM

I assume you're talking about the 1/2 and 1" rubber hoses that attach to the intake tube between the airbox and the throttle body. That's the PCV system, and you need it hooked up because it's measured air getting sucked into the intake. If you switch to breather filters it will not show enough flow going through the MAF sensor and will cause problems. The 1" hose is the idle air inlet, and it really needs to be hooked up.

#4 tallwelder81

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Posted 19 August 2012 - 01:27 PM

thank you both very much!!

p.s. fairtax.
if you are single, my ex fiancee is very pretty, and very sweet, and she moved to lake monticello, Palmyra a year ago. she is great, she just lives too far away and the 4,000 mile thing wasnt cutting it. she is 25. and 5'0" and in good shape. not a toothpick and not a whale. when she walks into a bar, every guy stares.

i could hook y'all up. just sayin....
she is kinda half dating some pot dealer now. anybody cool enough to like subarus must be an improvement.

not that im anti-pot. its all good.

#5 GeneralDisorder

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Posted 19 August 2012 - 01:48 PM

It's a bad idea for engine longevity to remove, reroute or redesign the PCV system. It removes harmful blow-by gasses that will foul your oil. The popular valve cover breather filters are for race and off-road vehicles that change their oil every hundred miles or less. Under those usage conditions there is not enough oil fouling taking place to matter. If you plan to leave the oil in for 3,000 miles then you better have a working PCV system.

There are no hoses on the (very simple) EJ hose system that can or should be eliminated.

GD

#6 tallwelder81

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Posted 20 August 2012 - 01:07 PM

shut up, gd! you dont know anything about subarus.






....just playin.... thank you for advice.

#7 Gloyale

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Posted 26 August 2012 - 12:52 PM

There are no hoses on the (very simple) EJ hose system that can or should be eliminated.

GD


I eliminated my IAC hose. But that's it.

The reason is that I'm using an intake plenum that doesn't have an IAC port.

Takes a few few seconds holding the gas pedal on cold mornings.


As GD stated, you do definately need the PCV hoses. Sore Thumbs aren't necessary.




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