Vacuum line off air box

DetergentCandy · Post by **DetergentCandy** » Sat Feb 09, 2013 8:50 pm

I was bleeding my clutch today, and snapped the hard plastic vacuum line that comes off the air box.
Didn't really have a choice at the time so I just capped both ends.

Do I even need this line? Or can I cap it off at the T closer to the turbo? I assume it's not necessary as it's not throwing a code, and all it was doing before was breathing clean air from the air box.

And none of the vacuum rewiring diagrams on the SRTForums even show this line existing.

RayWolf · Post by **RayWolf** » Sat Feb 09, 2013 9:36 pm

that line is for your pcv system.
It feeds air from your air box to your crank case.

you really should run the line to its own filter if you dont want to fix it with a new elbow.

I have that elbow piece but not the little line for it.

DetergentCandy · Post by **DetergentCandy** » Sat Feb 09, 2013 9:59 pm

You're thinking of the line that goes to the side of the air box, Ray.
This is the line that comes off the side of the air box intake tube.

It Ts into the turbo.

Post by **occasional demons** » Sat Feb 09, 2013 10:00 pm

You want to at minimum put a mini filter on the nipple for the air make up on the VC. You will otherwise be pulling a vacuum in your crankcase.

If you hear a strange noise developing, it is the crankcase being under too much vacuum. I had that happen on my SOHC, the tube got plugged or kinked, can't recall, but I kept getting this weird noise. Finally pulled the line off the back, and the sound disappeared.

Post by **occasional demons** » Sat Feb 09, 2013 10:12 pm

Could it be to the TIP sensor then?

DetergentCandy · Post by **DetergentCandy** » Sat Feb 09, 2013 10:36 pm

It's definitely not the VC crankcase vent

That's still plumbed into my air box.

Going on that diagram, i'm pretty sure it's this guy:

RayWolf · Post by **RayWolf** » Sun Feb 10, 2013 2:47 pm

Looks like its for evap from the purge solenoid.

DetergentCandy · Post by **DetergentCandy** » Sun Feb 10, 2013 4:12 pm

So can I leave it cap'd off?
Or do I need to uncap it?

RayWolf · Post by **RayWolf** » Sun Feb 10, 2013 9:07 pm

Idk I've never worked on an srt 4.
Idk what is best.
Usually best to keep all lines hooked up they way they are.

DetergentCandy · Post by **DetergentCandy** » Sun Feb 10, 2013 11:37 pm

Just checked AEMs install instructions for their CAI, and they have you plumb this line back into their unit.
So...I suppose I should hook it back up?

Post by **occasional demons** » Mon Feb 11, 2013 2:44 pm

From the looks of the diagram, there are a few check valves there. It appears that the line would let boost pressure back into the intake via that line. Seems kind of odd logic. I would think they would just have the check valve keep boost from going to the Purge valve period. To me the way the diagram shows it, it would be a boost leak. But then no one claimed the diagram was accurate.

I basically saved the image to my PC and enlarged it to see what the tees and valves actually were.

But I would just put it back to stock form.

MyNeonSaysHi · Post by **MyNeonSaysHi** » Mon Feb 11, 2013 3:01 pm

It is known as the "factory boost leak" Because during a boost leak check you have to cap the line off or it leaks boosts. Remember getting a 3/8ths inch extension and jamming it in there when I did have it hooked up when stock.

Its emission crap from what I have gathered. It is not needed. I have had mine capped for like 5 years with no issues on my PCM controlled boost SRT-4.

I remember reading about it helping the evap canister/charcoal canister crap. Just keep it plugged and I bet you gain more PSI due to not having that leak.

Post by **occasional demons** » Mon Feb 11, 2013 3:06 pm

As long as there is still vacuum to the solenoid, you shouldn't get a CEL. There needs to be some flow through there, or you will get a purge flow code about every 4 to 6 months. (I know from not having the line hooked to vacuum for a while)

DetergentCandy · Post by **DetergentCandy** » Mon Feb 11, 2013 3:57 pm

Interesting! I do remember hearing about plugging that line while doing a boost leak test, or it just lets all the air out of the system.

So i'm gonna leave it capped for now, and keep an eye on my boost levels for the next few weeks.

"Factory boost leak"? No thanks O:

MyNeonSaysHi · Post by **MyNeonSaysHi** » Mon Feb 11, 2013 4:16 pm

Quick google search.

http://www.srtforums.com/forums/f169/fa ... ne-604243/
Note BOOSTCRZY's post

DetergentCandy · Post by **DetergentCandy** » Mon Feb 11, 2013 4:45 pm

Alright. So if i'm going to be in boost for an extended period of time I may wanna uncap it.
But I daily drive my car, never taken to a track, and really don't plan on it. At least not anytime soon.
So i'll leave it capped for now. If they removed it from the PT Turbo, then i'll take my chances.

theColonel · Post by **theColonel** » Mon Feb 11, 2013 6:03 pm

DetergentCandy wrote:Alright. So if i'm going to be in boost for an extended period of time I may wanna uncap it.
But I daily drive my car, never taken to a track, and really don't plan on it. At least not anytime soon.
So i'll leave it capped for now. If they removed it from the PT Turbo, then i'll take my chances.

I had to change my piping after I went to the Hahn Cool Ram intake, and went to a lot of trouble to fabricate a "source" for that line.
I thought it was needed to operate the solenoids. I'm very interested in knowing how your car runs with it capped. It'd be nice to lose
a potential loss of boost, and simplify my "jerry-rigged" air intake pipe.

DetergentCandy · Post by **DetergentCandy** » Mon Feb 11, 2013 6:24 pm

I'll update this thread as I go! So far it's only been two days

But no CEL or blown up gas tank!

MyNeonSaysHi said he's been going 5 years without complications.
And Zenkat(SRT Forums and local) says he's going 7 years on his built car without it.

theColonel · Post by **theColonel** » Mon Feb 11, 2013 6:53 pm

^^^^ your driving habits are like mine ... street driving - no racing - and my engine is nearly stock. I've had problems in the past
when changing pollution control devices, and the turbo makes things more complicated.

Post by **occasional demons** » Mon Feb 11, 2013 8:14 pm

Looking at the diagram again, it seems more like a fail safe against the check valve that is in line to the purge control valve already. The first one should keep boost from leaking.

But if the one that goes to the air inlet wasn't there, it would put boost pressure through the purge into the fuel system, if the first check valve failed. So it acts as a pressure dump in that event.

Technically, you could just leave it open to the atmosphere, as it will only let pressure out, and not in. (Atmosphere pushing against vacuum) I bet they plumbed it to the air inlet more to keep noise down if the first check valve fails. Wouldn't want to make a problem to obvious. You may not take it to the dealer if it was easy to find.

If you have to plug it for a boost leak test, I would say the check valve is failed/failing anyways.

theColonel · Post by **theColonel** » Mon Feb 11, 2013 8:42 pm

^^^ I'm afraid you're over my head ... Would it be best to only plug the hole in the pipe that goes between the K&N filter and the turbocharger inlet ?

My car is so noisy, any added noise from the open line wouldn't be noticed.

MyNeonSaysHi · Post by **MyNeonSaysHi** » Mon Feb 11, 2013 11:09 pm

OMG I think there is too much thought into it. I thank Bill for trying to explain how it works. I just know there are a TON of people that don't run it and are totally fine. Nothing to fret about.

theColonel · Post by **theColonel** » Tue Feb 12, 2013 7:07 am

MyNeonSaysHi wrote:OMG I think there is too much thought into it. I thank Bill for trying to explain how it works.

I wanted to know how it works. It's because of this forum, that I was able to get rid of the catalytic converter,
running the stock PCM with no "check engine light".

Post by **occasional demons** » Tue Feb 12, 2013 7:45 am

Basically what I was saying, is if the check valve from the plenum side of the TB to the PPS is working, there should be no boost leak, and really no need to cap it. The line to the nipple pictured is only a boost dump line in case the check valve fails. If you were to develop full boost to the fuel tank, it could very well rupture.

If I were to "cap" it, I would just use a loose fitting vacuum cap, that would pop off if it did see over 15 pounds at the cap. Even 15 psi might split the fuel tank, if it seen it for very long.

Just 5 psi air pressure can swell a 55 gallon drum pretty impressively.

I would be more concerned about keeping the primary check valve in good shape by just replacing it if it leaks, than simply capping off the pressure dump.

I mean there is cheap, then there is stupid cheap. A $20? check valve is cheaper than a slightly potential ruptured fuel tank, and tow, or worse.

I mean think about it, you are not really preventing a small boost leak. It is just going into the fuel system area, depending on the fuel level, it could be pressurizing a small or large volume of air. when empty, it will take more time to build pressure, so that boost is just escaping anyways, as long as the PPS is open. Your cap isn't doing anything positive for performance at that point.

DetergentCandy · Post by **DetergentCandy** » Tue Feb 12, 2013 11:35 am

occasional demons wrote: If you have to plug it for a boost leak test, I would say the check valve is failed/failing anyways.

But it does leak, even if brand new. When you pressurize the system for a leak, you're supposed to cap that line or all your air will escape.
I remember I was confused the first time I did a boost leak test. I couldn't figure out where all my air was going, until I read the how to where it says to stuff a wrench extender in the line to plug it O:

So it dunno. Why would it leak like that from the factory if it's not supposed to?

Post by **occasional demons** » Tue Feb 12, 2013 2:05 pm

Cheap parts? ::Shrugs::

I would find a better check valve to put in the line. I mean why bother, if it does leak? They should have just put a restricting orifice in there if that was the true intent.

On the flip side, if the one in the dump tube leaks, it would be a vacuum leak. On a hard decel, it is holding back nearly 28 to 30 psi., between the vacuum on one side, and atmosphere pushing on the other. Pretty sure you are not pushing that kind of boost in stock form.