Vacuum hose question

[JIMSVX]

I'm getting ready to put my intake manifold back on and I'm using the vacuum schematic on the inside of the hood as a guide. I have everything figured out (I hope) except for one thing. The item that mounts on the bottom of the manifold called the "Vc tank" has 2 hoses connected to it. One goes to the "Induction solenoid valve", also mounted on the manifold, and the other goes to a "Check valve". The other end of the check valve is shown connected to a hose that doesn't go anywhere. Is that just vented to the atmosphere" I can't find anything on the engine where it looks like it should be connected. Am I right on this or am I reading the schematic wrong?

Also, what is the Vc tank? I think I understand everything else except what this system is suppose to do.

Thanks - Jim

[oab_au]

I'm getting ready to put my intake manifold back on and I'm using the vacuum schematic on the inside of the hood as a guide. I have everything figured out (I hope) except for one thing. The item that mounts on the bottom of the manifold called the "Vc tank" has 2 hoses connected to it. One goes to the "Induction solenoid valve", also mounted on the manifold, and the other goes to a "Check valve". The other end of the check valve is shown connected to a hose that doesn't go anywhere. Is that just vented to the atmosphere" I can't find anything on the engine where it looks like it should be connected. Am I right on this or am I reading the schematic wrong?

Also, what is the Vc tank? I think I understand everything else except what this system is suppose to do.

Thanks - Jim

I haven't had the manifold off to look Jim, but the lines run from the inlet manifold to the check valve, to the vacuum tank,to the Induction control solenoid, to the Induction actuator. The pipe to the check valve picks up vaccum from somewhere? there will be a pic of the under side of the manifold in somebodys locker, to show where it gets the vaccum from.

The system is to operate the Induction control valve to change the inlet system from Inerta to Resonance. The check valve and tank is to hold enought vaccum to operate the valve, as when the throttle is wide open there would be no vaccum, to operate it.

Harvey. ;)

[JIMSVX]

Thanks Harvey. After I read your reply I went back and looked around the underside of the manifold. What do you know, there is a vacuum tap on the manifold right under the vacuum tank. Now I just have to be careful to mount the check valve the right way! :o

I did a search on this system and your name, and I found This link (http://www.subaru-svx.net/forum/showthread.php?t=11411) . Your explanation of how the IRIS system works made it all very clear. Thanks for helping me understand it. Now all I have to do is wait for gaskets, etc., so I can start putting it back together.

- Jim

[PhatWeasel]

I have a vacuum leak that is causing rough idle when the engine is cold and in the process of warming up. It seems to run fine when warm. After starting cold I can hear a leak, sounds pretty major, coming from the passenger front of the intake manifold. Seems to be in the area of the VC Tank/Reservoir. After the engine warms up and idles smooth, the vacuum leak goes away. When I advance the throttle a small amount, the vacuum leak sound returns. This leads me to beleive that the leak is not intermittant, but the result of vacuum switching. I have sprayed the area with throttle body cleaner (while the leak sound is present) and the engine will stumble slightly but I have not been able to pinpoint the a source for the vacuum leak. The leak does not seem to be either port on the VC Tank/Reservoir as they are fairly accessible and I gave them a direct jet of T/B cleaner with no change in RPM.

Question 1: Is there a vacuum circuit that is closed when the engine is at idle and opens when throttle is applied, assuming a warm engine?

Question 2: What failures have been seen with the under-intake vacuum lines when the intake manifold has been removed and reinstalled.

I had the vehicle in for service to replace a really stuck PCV valve and I think that may be the source of the failure. They had to remove the intake to get the sticky thing out. I am SOL as far as any warranty work is concerned, it has been far too long at this point since the service was rendered.

Thanks,
-Nate

[JIMSVX]

Nate - There are several vacuum hoses under the manifold. After you pull it off the block some of them stay with the manifold and others are attached to various parts on top of the block. Immortal_subi has several pictures of both these locations in his locker HERE (http://www.subaru-svx.net/photos/user.php?immortal_suby|3116).

A diagram of the vacuum hose routing is located HERE (http://serial.cc/vacuum.jpg).

As far as failures with these hoses are concerned, assuming all the hoses are original then it is safe to say that one or more could have cracks which would cause this problem. After 13 years of constant heat on top of the engine they all probably need to be replaced. At least that was my experience when I replaced all mine.

A tread discussing the removal of the manifold is located HERE (http://www.subaru-svx.net/forum/showthread.php?t=3641&highlight=vacuum+diagram).

Good Luck

[PhatWeasel]

Thanks for the reply Jim,

I was hoping to avoid removal of the intake manifold. After posting the questions I went back down to the garage for a second look and I've determined you are right, it's high time to pull the manifold and just get the project over with. I can also vacuum out all the foliage and replace some wire loom coverings while I'm in there. Not quite what I wanted to do for Christmas, but it needs to be done.

Thanks for the vacuum diagram, much easier to read inside the house than the decal under the hood.

-Nate
73 de NF7X

[JIMSVX]

Good Luck Nate. Just remember to take your time when you are ready to lift it off the block. There are a lot of interconnections between the two, both electrical and vacuum tubing. It's real easy to break something.

I see you're a ham. I'm K0UYO, been a ham for 49 years - Wow, that's a long time! :eek:

[SVXRide]

Note: the one way valve that is inline from the tap on the intake to the vacuum tank for the IRIS has a history of cracking with age, causing a vacuum leak and elimination of the function of the IRIS. Easy to check, as you can actually get to it from the front of the engine;)
-Bill

[JIMSVX]

I agree Bill. The check-valve on mine was cracked and very brittle. SVXFILES has several pictures in his locker here (http://www.subaru-svx.net/photos/user.php?svxfiles|24710) that show where to find the thing.

Subaruparts.com has it for about $17, a lot of money for such a small plastic part. :eek:
But it's worth it if it solves the idle problem.