Unresponsive boost gauge

[SEAN-NZ]

Found out something today during general pissing around with engine bay stuff lol. The boost gauge is plumbed in where the pipe runs off the intake manifold to the blow off valve via a T piece, the problem is that the gauge is slow to read, but with bov line disconnected from T piece and the hole blocked up the gauge is much more responsive, put the pipe back on and it's slow again, any ideas on this? Or a different way to plumb it to stop the issue.
Another thing that just has me wandering, with the bov pipe disconnected the bov still blows off when I change gears, don't have any pics as I am on my phone and also don't have car with me lol, can get pics tomorrow though

[Davezj]

do you have a stock factory set up of aftermarkeet bov?

most people have the boost gauge coming off the back ofthe plenum chamber after the throttle body, the smaller of the piipes the larger one goes to the brake servo. you can try moving the t piece to there.

[elnevio]

do you have a stock factory set up of aftermarkeet bov?

most people have the boost gauge coming off the back ofthe plenum chamber after the throttle body, the smaller of the piipes the larger one goes to the brake servo. you can try moving the t piece to there.

I know Dave doesn't mean it this way, but don't tee off the pipe that feeds the brake booster. It'll work, but it is an MoT failure.

[Adam.Findlay]

and the brake booster line has a one way valve in it to stop boost presaure entering the brake booster so it wont work for a boost gauge. i take my boost gauge off the smaller line next to the brake booster one.
if that doeant work check for leaks/torn vac lines in the vaccum system

[Davezj]

yes your right nev, i meant tee it off the smaller pipe.
it did not come accros quite right.

[SEAN-NZ]

using the smaller pipe as i figured its a bad idea to use the one for break booster, its an aftermarket bov that as far as i know is using all the stock piping, if i have it set up as the pic shows the gauge is very responsive, and the bov still blows off, with the pipe connected, thats when the response sucks, got 2 vids on youtube of it, links below, should be easy enough to tell the difference between the 2 lol.
Just as a note, i did block off the open end of the t-piece when i pulled off the bov line, didnt bother blocking the bov line though.
http://www.youtube.com/watch?v=PRWYO6Ejc0U
http://www.youtube.com/watch?v=MTJWWQQ5wls


IMG_02451.jpg

[Davezj]

from watching the vids,
i can think of 4 senarios it could be,
1. the pipe work to the boost gauge is very restricktive, e.g. the pipe bore is too small or the T piece bore is too small. even if the pipe and T piece were supplied with the gauge they could be wrong, friend of mine had a similar issue and the T piece brach that goes to the gauge had a tiny hole compared to the straight through air passage which meant the gauge was very sluggish too respond and would not read over 0.5 bar even though the boost was getting up to 0.9bar. i replaced the T piece with a equal bore on all 3 ports and this solved the issue, any T piece will do, from a fish tank, from the bonnet water jet as a test fix, etc, etc.

2. there is a leak in the pipe going to the BOV, from the T piece.

3. you have the BOV end connected worngly some how.

4. the BOV has an internal leak.

as for the BOV blowing off when pipe is disconnected that is odd. maybe reinstall the original recirc factory valve to eliminate this from the problem
you need to check all the pipe work very carefully and even replace it, or remove it inspect it and reinstall it, or do a boost leak check this will show up any leaks.

hope this helps

[SEAN-NZ]

the pipe to the gauge is very small, thought of that myself but figured as with the bov disconnected the gauge worked fine that the pipe must not be the issue, the pipe going to the gauge is the white one, for the bov possibly leaking, i dont actually have the original, the car came with the one it has, says on it that its a greddy one, not sure how old it is, or if its even legit, dont know if people make fake ones or not lol, wouldnt be surprised if its leaking, i do hear a whistling when the car comes on boost, im just very lazy and havent done a boost leak test yet, il take a look at the pipework when its not dark, to bad its so hard to follow pipes in the engine bay lol, could i try pulling the vac line off the bov and see what happens then? i suspect it shuldnt blow off and would it leak like mad?

[Davezj]

the main reason for point 3 is it ensure the pipe you think is going to the BOV is actually going to the BOV.
as you say it is hard to tell where the pipework goes.
i presume you have the engine cover off, as this will make it easier.

[SEAN-NZ]

got a pic of the bov, as far i can tell from the net, its a greddy type s or rs, even with the vac line that is on the right of the bov under the recirc pipe disconnected it still blows off, doesnt seem any different to normal, couldnt get the line to seal with tape so disconnected other end and sealed the t-piece, must say, the pull was pretty epic, havent felt it like that since i got it lol, that was hitting about 9psi before trailing off to between 5 and 7 as its always does, just felt a lot quicker than usual

IMG_0283.jpg

[Davezj]

sorry i am not following what you did.

to test the pipe work,
1. disconnect the vac pipe from the BOV seal it off, fold it over on itself and secure with a cable tie.
2. do the same idle rev test you did on the vids.

if the boost gauge responds quickly then the BOV pipework is ok and there is an issue with the BOV
if the gauge is still sluggich then the issue is with the pipework.

firstly you have to verify if the pipe going to the BOV is the same pipe going to the T piece,
1. with engine running at idle disconnect BOV end of the vac pipe and verify there is a vacuum being created.
2. then disconnect the vac pipe at the T piece, go back to the BOV end and verify the vacuum is no longer present

if this is the case then it is the same pipe if not then it is likely the pipe which was connected to the T piece do not have anything connected to it any more.
to test this do the following.

1. blow down the pipe that was connected to the T piece and see if it is blocked or free flowing
if it free flowing then it is probably disconnected. trace the pipe and find out where it goes.


and so on and so on.

[SEAN-NZ]

I disconnected the vac pipe at bov end, the boost gauge then displayed zero vac that was before I blocked off the bov end of the vac line, when I blocked off the vac end the gauge went into vac and had the response that its meant to have, although I couldn't get a perfect seal so it was only at about 15 inches of vac, so I disconnected the end at the T and blocked off the T to get a proper seal, which achieved an accurate vac reading, with both end disconnected the gauge was as responsive as it should be and the bov was still perfectly functional, I tried googling the reason why it was still working as it should but couldn't find anything

[Davezj]

So your pipework seems to be ok, from that description.
So when you revved the engine with the disconnect and vac pipe blocked, you got the quicker response from the gauge not just a static vac reading. If so then it points to the BOV being faulty with some kind of leak.

Sorry to be so pedantic but I can't see what you see only what you write, and most thing are open to interpretation, which is why I ask.

As for why the BOV is still opening I am not sure. But let's try and reason it out.

As I understood the operation of a BOV when under any normal condition the pressure on both sides of the BOV actuator and the valve is held shout via the spring in side the BOV then when you release the accelerator the vacuum is applied to one side of the BOV actuator and the boost pressure is strong enough to force against the spring and the valve opens.
So now I read this back if he vacuum pipe is removed once the boost pressure rises high enough to over come the BOV internal spring the valve will open, so when accelerate the BOV will open and bleed off boost pressure.

If I have the operate correct.

[SEAN-NZ]

i think you have it right, with the pipework disconnected and the T blocked, i get the good response, from my understanding of what you said about the bov, it opens because the boost pressure spikes high enough when i take my foot off to force the spring open when the vac pipe is disconnected, making it operate how it normally would just without having any actual vacuum applied to the bov.
I have suspected a leaky bov for a while, just never really got around to doing a test, i suspect it becasue i can hear a whistle when on boost that sounds like its coming from where the bov is located, although i may just be hearing it wrong

[Davezj]

It would only be a small leak where ever it is.
I am not sure how you test it though.
The leak would be between the vacuum actuator part of the BOV and the main BOV air channel. You would probably need a hand vacuum pump to test it. Attach it to the vac input of the BOV and if the BOV is ok it should old a vacuum and the valve in the BOV. Should open at a predefined pressure, set by the manufacturer.

[SEAN-NZ]

ahh, i thought about just testing if the bov was leaking, didnt even think about the vac side lol, prob easier for me to just borrow my mates for a bit lol

[SEAN-NZ]

so i pinched the bov off my mates vr4, just the standard plastic crap, still did the same thing, i really am stumped at why this is occurring, unless the fact that the bov adds more air causing the line to the gauge to not be able to fill fast enough? really dont see how this could be the case though

[wintertidenz]

I'd double check the vac line pipework again - the BOV line comes off the turbo wastegate line. It's possible that you have a damaged pipe or incorrectly placed pipe.

[SEAN-NZ]

thought the bov line ran straight from the intake manifold to the bov? or does it connect to the wastegate line somewhere?

[Davezj]

have a look at the jap workshop manual PDF's in the library for the correct boost connections.

http://www.clubvr4.com/forum/showthr...hop+manual+pdf
section 13A part 1 page 4 has the boost pipework diagram on it

between the intercooler and the throttle body you can see the recirc BOV the vac/boost feed for it comes directly from the plenum chamber the other side of the throtle body. where as the vac/boost feed for the wastegates comes from the pipe work between the intercooler and the throttle body.