How To Check Vacuum Leak

[KJS]

Let's say you want to check for vacuum leak or boost leak

you have a bottle of Aerostart/Start Ya

which part you should be spraying when the car is idling?

can someone post a picture of the engine bay and circle with red lines? (assuming the car is R33 RB25DET S1)

there are so many hoses and pipes....(I am afraid if I spray the wrong place and the car goes flaming)

if there is a leak, the rev will change right?

[Julz89]

what i usually use is brake cleaner or some areosol cause it will make the car run roung. spray anywhere around the intet manifoldand the hoses that are around it, also see if u can get hold of a vaccume gauge and shuld tell u wat pressure ur running.

[GeeTR]

Many automotive aerosols spray a volatile liquid, so when ingested and subsequently combusted, will often offset the air leak, causing the revs pickup.

Brake cleaner is used, as it drys without leaving a residue.

I doubt you'd have any chance of igniting the spray, bar spraying it on a red hot manifold (even then...)

Before following your mates advice, trying pressuring the inlet tract with a air compressor / servo tire compressor. Look around (300ZX club) theres basic instructions on making a AFM sized plug (PVC end cap) with a tire valve tapped in; they're priceless and have helped many people I know.

Edited July 28, 2008 by GeeTR

[KJS]

the thing is... I sprayed around and there is no any changes in the rev or whatever (except the exhaust because my mate said could ignite)

however when I drive, there is psstt sound....which is quite loud

even when I am hearing music and closed windows, I could still hear the sound (sounds like gas leakage)

it is from the left side of the front

my car is stock and the pod filter is not properly mounted but just tied properly and connected (so one side of it sort of kissing the chassis of the car)

the mechanic said the engine sound is good, doesn't seem like there is a leak (but he hasn't heard the sound when it is driving)

and also after changing o2 sensor, still getting only 300kms per tank.

so, I suspect I didn't spray every parts which I should be to find the leak

or the sound could be due to the friction between the air entering the pod filter and the chassis

actually the sound, instead of describing it as pssssttt, I would say it sounds like suuuuuuu

by the way, the car is auto, sound starts to get loud after 2300rpms or climbing a hill.

what do you guys think?

so anyone has a picture of where to spray or just where cannot be sprayed.

any other way which is slightly easier for a newbie to identify?

[GeeTR]

any other way which is slightly easier for a newbie to identify?

A PVC end cap, tire valve and a servo air compressor is about as easy as it gets hey

[Travo]

A PVC end cap, tire valve and a servo air compressor is about as easy as it gets hey

agreed - search the forums for this easy to make device as this saved me so much drama its not funny - best of all it cost me about $3 and 5 mins to make!

[Julz89]

ok this might sound stupid but are any controls vacume controlled like heater air con etc??? cause it culd be somethin behind the dash.

[SDEWY5]

another obvious one that mite b the problem, though u have probably checked it, the vacuum line to bov, taking that off will cause bov to open when it boosts up, leaking off boost press.

[KJS]

another obvious one that mite b the problem, though u have probably checked it, the vacuum line to bov, taking that off will cause bov to open when it boosts up, leaking off boost press.

it is not taken off, still there.

[phatlavish]

try using some soapy water (dishwashing liquid or handwash stuff), apply a bit of it round the various joints on your intake piping.. if theres a leak there it will make some small bubbles

Are ya just using the stock sidemount? might have a hairline crack somewhere on the core thats hissing once it hits boost

[KJS]

the idling is...around 850rpms

this is an auto car so I can only approximate

when it reaches around 60km/h I could hear hiss sound, before that, there is a very very very slight hiss (not constantly but sharp, on off)

when it reaches 80km/h, I could hear pssssstt....with windows closed and music on

anything beyond 110km/h I could only hear suuuuuuuuuuuuuu

between 80-110 there will be two-three sound, the obvious one are turbo and pod filter, but there is another psst sound (weaker sound) ....

most likely there is no boost leak because the car doesn't stall

everything is stock, so the sidemount should be lol

I have a question, the PVC endcap, what diameter should I be buying? what is the diameter of the AFM?

[abu]

RB25 AFM is 80mm, same with RB20 and Z32

[Adriano]

Doesn't sound like a vacuum leak, it sounds like a boost leak, which wont be picked up by spraying brake cleaner. Pump up the piping with a bung in the AFM

[KJS]

Hi everyone! I just used the method which I was told here and tested for leak.

What I did was, using a round container bought from BigW (the bottom is approximately 80mm diameter) and a tubeless tire valve from Repco. Then combined these two things and found a petrol station (aka servo), with manual pump and tested it out.

My friend took off the AFM, and then we put in this container, pump it up.

There is a sound......an air leak sound, which is around the place near the turbo. According to my friend that place are mostly metal piping.......so we couldn't do anything. We could hear the sound, and it is from the area where it is near oxygen sensor, turbo.....that area there....but we don't know excatly where the sound is from or could be from.

Then after I start the car, we could hear another two sounds. One is from the stock BOV.

The other is from the intake manifold, which is on top of the engine.

These two sounds weren't heard when I was using the pump, but was only heard when we start the engine.

So here comes:

my friend said the sound from the turbo or area near the turbo...he doesn't think it will affect the fuel consumption tho and that is what we heard from the result of the leak test.

so what does that mean?

I wonder......anything serious?

what could be the reason with everything stock and getting 14.68L/100kms instead of 11.24L/100kms?

I really rarely hit the boost.........usually drive below 2.5k rpms and yet still.....

if I would to send to a mechanic (AMEC at Cooparoo), what should I tell him?

[sonoramicommando]

ok guys

i need to do this thing as well (supposedly i have some air leaks), but i have a couple of questions:

- do i need to have an air source that maintains constant pressure, or can i just use a footpump to get it to a certain psi and listen for a leak?

- can someone explain it to me how it actually works? i d imagine valve overlap would allow the built up pressure to escape to exhaust side?

thanks

sam

[daisu]

Use soapy water to identify where leaks are coming from.

Put some decent pressure in through the tyre valve cap. You're right that air will go out through the exhaust (that's possibly the sound you heard near the turbo) An air compressor is a good idea because you will get good pressure in your inlet piping.

[sonoramicommando]

Use soapy water to identify where leaks are coming from.

Put some decent pressure in through the tyre valve cap. You're right that air will go out through the exhaust (that's possibly the sound you heard near the turbo) An air compressor is a good idea because you will get good pressure in your inlet piping.

ok after having done this with a garden sprayer, i really do need a compressed air source with constant pressure and flow rate.

anyway, i found out that there were massive leakage (at least it seemed so) at vacuum hoses (not clamped well enough) and where injectors go into the manifold. i could hear some decent whistling noise (which got more obvious with soapy water over it).

now i tightened up hose clamps and replaced the injector insulators but i can still hear air flowing over somewhere in the plenum.

is this normal to be able to hear air flowing sound (less of a whistle now) - which im hoping to be air flowing thru the head with valve overlap - or do i still have leakage? i couldnt quite confirm if i got rid of leakage at underside of intake manifold, so it could be a possibility.

cheers,

Sam