What's the Purpose of the Small Hose on the DV?

[GazW]

Hi All,

Can anybody explain the function of the small hose on the DV?

I guess it opens the DV a the correct time to reduce boost, doesn't it only do this upon closing the throttle or at other times as well i.e underload?

 

[LiCkWiD]

It is literally on-top of the original DV?

it's a Vac hose mate.. it recirculates air, I do believe. Remove it and you get the noise some people call "actuator flutter" or "wastegate chatter"... both non-existent noises. The chattery noise is turbo-charged air washing back over the turbo's blades as the throttle plate closes.

Basically, remove the pipe from the top of the DV and you're removing the recirculating property of the DV.

 

[G2232]

yeah your right mate that is the vacuum hose is the hose that is conected to your inlet manifold that creates the vacuum when the trottle body is closed resulting in the DV to open and release the built up pressure allowing the turbo to resume spinning (in correct direction) so as not to exert un-neccesary pressure and cause turbo stall

 

[GazW]

Does the ECU adjust the amount of VAC to this line? Or, is it just connected directly to the intake and as you close the throttle the decreased pressure opens the valve?

 

[LiCkWiD]

Well the purged air returning from the throttle plate is under pressure, so the vacuum suction on the line just accepts it all and dumps it back into the air-box.

I'm unsure whether the strength of the vacuum is ever adjusted, let alone via the ECU. Seems a pointless endeavour.

 

[G2232]

the volume of suction created is directly related to the volume of pressure.
So as pressure is increased so does the suction

 

[GazW]

My Cupra has had a Forge DV fitted at some point; the extra height of this DV has cause the vac line to get compressed against the engine cover. I get a rattle under acceleration and was wondering if restriction in this pipe could cause a rattle.

 

[LiCkWiD]

It's a flexible hose with a fair bit of give in it, although it is fairly strong. There's a possibility it's causing the Forge DV to bang against something else, though.

Have you tried cable tieing it down to something to prevent motion of any kind under acceleration?

 

[GazW]

I’m not sure if it is from the DV rattling around; it’s been getting worst over the last few months. That’s why I though it might be the vac line on the DV getting compressed over the last few months

 

[G2232]

does it rattle constantly when the engine is running?

 

[GazW]

Nope, under accleration and upto about 3000rpm

 

[G2232]

well if its when accelerating it cant be anything down to the vacuum hose as there would be no vacuum as the throttle plate would be open.
So i could only say it must be the dv vibrating againt something

 

[LiCkWiD]

Hence securing it down.

Odd that you'd hear it in the cabin though, mate. Due to the height of the 007p.. it'd only knock against the bonnet insulation, surely? And that'd be a thud or knocking, as opposed to rattle.

Hmm... :S Hope you've got your detective hat on.

 

[cupra@180]

From looking at mine the 007 I have installed seems to be under the engine cover. Remove engine cover see if it still happens. I had a noise because my engine cover was loose and was vibrating against the vac pipe.

Best of luck mate.

 

[GazW]

I'll give it ago tomorrow, put the cover in the boot on my way to work

 

[Feel]

I had a big fat "EH?" popped into my head when I read this thread...

The small hose off the "top" of the DV is the vacuum hose - it reduces the pressure on one side of the piston (or diaphragm if you have one) and opens the DV when the throttle plate closes.

Because the other end is connected to the inlet manifold, when the throttle plate/butterfly shuts the pistons suck the remaining air out of the inlet and create a vacuum.

The N249 is in this line between the DV and the inlet manifold, and the ECU can use the vacuum stored in a reservoir to monkey around with the DV.

The vacuum hose doesn't recirculate the air back into the TIP, that's one of the two 25mm hoses, the other 25mm comes off the charge side of the turbo.

If your vacuum line is rattling against something, you could try reversing the DV (physically turning the DV to swap the two 25mm connections around) which would reposition the vacuum hose., but I doubt you'd hear a rattle caused by the vacuum hose.

Alternately, when you're at full throttle, the pressure in the charge side 25mm might be moving the DV so that it rattles against something.

 

[GazW]

Hey Phil, thanks for you reply.

I had a quick look at the DV this morning. It doesn’t look like there is anything that it can be rattling against. Removed the engine cover, one of the clips is missing. I put it in boot for the drive to work this morning but I’m still getting the rattle.

The vacuum hose it has been cut at some point (to fit a boost gauge) and connected back together. I’m pretty sure this isn’t leaking though.

Which way round should the DV be fitted? Does it matter? Mine is fitted with the VAC line coming out of the top of the DV.

The rattle is definitely coming from this area and only happens under load, ¾ to full throttle, up to about 3000rpm. What about the other valve in this area, the N75?

 

[Feel]

Doesn't really matter which way the DV is fitted, no.

The original location of the stock DV, is with the vac hose coming out the top. You could argue that this isn't actually the correct way round as for years DV were always fitted the other way round.

Personally, I can see that it doesn't really make a difference, but I would've thought that the way VAG have done it is right, as the charge pressure is pushing on the side of the piston rather than pushing against the spring. But, life's too short

People that have reversed the DV from the OE location have commented that it makes a different sound. Some like this different sound, some say it's gay.

 

[GazW]

I think I’ll stick with the non gay way. Any thoughts on what else this rattle could be? It’s doing my nut!

 

[Feel]

Could be anything. Are you sure it's from the engine bay? Exhaust heat shield? Something in the dash?