Please read before buying a Dump Valve

[ghanda]

I've had one annoying problem for a while now and tonight I finally solved it.
The symptoms:
The car almost stalls when coming to a halt after a fast run. It has actually stalled twice, the TCL lights have come on a few times, but mainly the revs dip to almost nothing and then pick up again.
There is a strong smell of petrol when you put your foot down in short sharp bursts.
There's a groaning sound between slow shifts.
And recently, I've noticed that it will start to lose boost if you try and hold 4K revs.

So, after much research on here, went through the probablr causes:

Lamda sensor voltages checked out fine.
Replaced the idle stepper. Slight improvement.
Checked all the hoses. No difference.

Finally tonight I got round to replacing my Vent To Air Dump Valve with an OE EVO re-circulating item. I've had the VTA on for almost two months and if I'm completely honest, may have noticed a slight drop in performance.

Only issue was that the smallest pipe was too short (?). After frantically trying to locate some tubing in my Garage , the only thing I could find was the tube that comes off my Pressure washer for putting into deteregent. It was the tiniest bit too small, however after much headscratching I used a heat gun to warm it up and slipped it on, and once cold again, the most perfect of fits!

Anyway, after patting myself on the back, time to go out for a test drive.

OH MY GOD.

No 'Pssht' in the slightest. Instant pickup, noticeably more torque, quicker gear changes....and most importantly...rock steady idle! :chugchug: :chugchug:

Off to bed now and to test it properly at Bedford tomorrow :)

[Bahama Dreamz]

so hold on simply put dont use a blow off valve or dump valve? because i have the same gas smell problem and i have very very bad low end. i mean i replaced the stock bov with an aftermarket one
nothin too special but i jus would like to know wat is casuing me to have that bad low end and the gas smell because i have the same exact problems you described

[ghanda]

YUp - simple as that. The VR has a 'dump valve' as standard, but the term is confused by a lot of people: Dump Valve, diverter valve, blow-off, etc, all the same. The difference is what they do with the air:
The standard item 're-circulates' the air. What people refere to most commonly as a 'dump' valve, 'dumps' the air externally (vents to atmosphere) to create the pshht sound.
From my limited understanding, our cars run an air/fuel monitoring device. The sudden lack of air in the system causes the MAF to dump more fuel into the system (hence the smell) and in my case also caused the stalling issues. Or something like that :)

[bernmc]

This is another one of those things that has been extensively discussed her. Quail came up with a very nice explanation (search for dump valve to get many oeiginal threads):


Theres 3 types of DV/BOV you can buy.

Recirculating -

Recirculates the dumped air back into the intake. The car's MAF sensor is expecting air to be recirculated. With recirculating BOVs, you wont get any dodgy idles or stalling, because the MAF is seeing the air which has been dumped and returned.

DTA (dump to atmosphere) -

These are the dump valves which make the loud dumping noise. They also cause you to run slightly rich on lift-off/overrun (because the MAF is expecting air to be recirculated, but instead the air is dumped to the atmosphere. This means the ECU is putting petrol in the engine, without the neccesary oxygen to burn it properly. This results in temporarily running rich (and sometimes getting flames when you get back on the throttle)). Running rich wont harm your engine, and everyone loves flames

Dual BOVs (recirc & dta)

These DVs come in a variety of shapes and sizes. Some will return the dumped air to your intake when your at crusing speed, but when at WOT will DTA. Some are adjustable, so you can tell them how much you want recirc'd, and how much you want DTA'd. The way to visibly see if the BOV is a dual, is it will have too trumpets. One will be flared (the dta one), and one will be hose sized to recirc to your intake. These are the compromise; should tackle the stalling problem found in some cars, whilst also giving you the noise when you want it.

[ritch_w]

there was a piece on DVs on 5th gear the other week, when the "expert" fitted it they did dyno runs before & after not for bhp but boost pressure or something

anyway an incorrectly fitted /adjusted DV can have a detrimental effect on performance - apparently :rolleyes4

[pezza]

As ghanda said... EVO reirc is the way :thumbsup:

There may only be a small amount of air recirc'ed (which helps keep front turbo spinning) but it makes the pickup in between gear changes bite more and pickup is quicker....

[jakester]

I shall have to adjust mine, I am seeing a couple of symptoms. I have a recirc+DTA, I assume adding extra washers to tighten the diaphram will recirc more air into the system as opposed to dta?

[Kieran]

I must comment here.

I am having similar issues to Gary - Spluttering idle, stinks of petrol when 'tapping' the throttle - Boost curve all spiky and also peeling back at sustained higher engine speeds.

The kicker is that I am running the standard VR-4 recirc valve. think that's what's happening with my recirc... I think the diagphram's split and it's 'dribbling' air out when it shouldn't be.

No idea what VTA valve you were running Gary, but could it have been leaking/incorrectly adjusted/not a strong enough spring? If all VTA valves caused trouble, then a lot more members would be having these issues I would have thought? :inquisiti

We'll know soon enough - I have just purchased the VR-4 specific SSQV valve and will fit it soon, to see if that cures the problem.

[ghanda]

Interesting to hear Kieran - it's a Forge EVO jobbie, so not a cheapy. Can the damping deteriorate in 2 months?
Put an OEM back on to prove the point - I'll be replacing it with an alloy re-circ, but first need to sort my brakes: I was at Bedford today, had an awesome time...but my brakes caught fire :) Will post in full later

[Kenneth]

Interesting to hear Kieran - it's a Forge EVO jobbie, so not a cheapy. Can the damping deteriorate in 2 months?
Put an OEM back on to prove the point - I'll be replacing it with an alloy re-circ, but first need to sort my brakes: I was at Bedford today, had an awesome time...but my brakes caught fire :) Will post in full later

maybe the spring in the VTA just settled in a bit and lost some tension. Any problem with your BOV in that regard is going to cause issues.

I have recently got a VTA valve and after spending a reasonably amount of time getting it setup correctly (checking how much it opened at idle, how quickly it re-seated etc) I have no problems whatsover... Idle is rock solid.

you could get yourself a MAP-ECU and solve your problems that way too /Hmmm

[pezza]

SInce we are all in BOV mode...

I have been testing a GFB hybrid BOV and found it would give a very short psst only at full boost in 1st or 2nd. Have adjusted the spring as much as I can but still the same thing... :( Do I have vauum/pressure problem..or is there not enough pressure pushing piston down?

Put the same valve in an evo FQ and whooosh Tssssss (technical term). this bothers me how it works in the evo and not my car? :inquisiti vaccum shows about 25 - 27inHg so not sure...

Thing is with both a stock and FQ recirc unit with recirc pipe detached, both devices VTA properly.. all very puzzling :inquisiti

I think I will have to stick with recirc...(which aint such a bad thing anyways) I will have to live with my airbox/induction whistle on lift off or do like some of the german petrolheads do .. either install a kazoo in my airbox or a whistle in my tailpipe /pan

[Quail]

Quail came up with a very nice explanation (search for dump valve to get many oeiginal threads):

I removed my MS Paint drawing from that thread though after bandwidth expiration!!! If anyone wants to see it let me know

[Kenneth]

SInce we are all in BOV mode...

I have been testing a GFB hybrid BOV and found it would give a very short psst only at full boost in 1st or 2nd. Have adjusted the spring as much as I can but still the same thing... :( Do I have vauum/pressure problem..or is there not enough pressure pushing piston down?

Put the same valve in an evo FQ and whooosh Tssssss (technical term). this bothers me how it works in the evo and not my car? :inquisiti vaccum shows about 25 - 27inHg so not sure...

Thing is with both a stock and FQ recirc unit with recirc pipe detached, both devices VTA properly.. all very puzzling :inquisiti

I think I will have to stick with recirc...(which aint such a bad thing anyways) I will have to live with my airbox/induction whistle on lift off or do like some of the german petrolheads do .. either install a kazoo in my airbox or a whistle in my tailpipe /pan

with the hybrid, you should have 2 adjustments.
1) piston pre-load - this determines how much boost you need to open the piston. set it hard and it wont open

2) VTA:Re-circ ratio - how much air is VTA vs re-circulated.

An idea might be to set it to fully VTA and then get the piston pre-load set correctly, then adjust how much noise you want

[bernmc]

An idea might be to set it to fully VTA and then get the piston pre-load set correctly, then adjust how much noise you want
HOw would you go about setting up the dump valve then - how do you know if the piston is closed at idle, particularly if you're replacing the std valve with a recirc? eg the forge valves come with three different sprins, and a couple of washes - I would'nt know where to start, and whether anything was working as it should be...

[AllBeItMine]

or realise that an evo fq probably runs over twice as much boost as your vr4 and the sound of 20-22psi escaping is always going to be louder/longer than the sound of 8-9 psi escaping

[Kenneth]

HOw would you go about setting up the dump valve then - how do you know if the piston is closed at idle, particularly if you're replacing the std valve with a recirc? eg the forge valves come with three different sprins, and a couple of washes - I would'nt know where to start, and whether anything was working as it should be...

In my DV I can look down the trumpet to see if the piston is sealing.

What I did was connect my new DV to the vacuum hose without being connected to the car. (standard DV was still installed)

I set the spring pressure just about as low as it would go, then start the car. adjusted the spring pressure until the piston closed.
Then blip the throttle (at the throttle body) and watch what happens to the piston. Rev high and then shut off, the piston should open.

Tighten the spring pressure on the DV until it does NOT open (it may move, but wont open the port. Don't tighten tooo much!) and then install.

from there you should be able to make minor adjustments if nessecary but otherwise it should be about right.

/edit: Oh, and I just remembered... with the car running, I used my finger to push the piston open and checked that it fully closed again. This is important. Also, the amount of pressure you need with your finger relates to what boost pressure is going to be required to open the piston