Hey everyone,

Just done some work on what I suspected was a leak in the intake somewhere causing a air hissing noise every time I put the accelorator down.

Found quite a few cracked or damaged hoses and these have all been replaced - also cleaned out the throttle body and the crankcase breather.

Put it all back together today and the noise is still there, and actually seems a bit louder!!

Any ideas what could cause it? Potentially a leak somewhere along the exhaust?

The loudness of the noise is specifically related to how open the throttle is (how much I press the accelerator pedal) and doesn't seem to be affected by speed at all, but gets louder the more open the throttle is.

It's quite loud and can easily be heard from inside the car while moving. It sounds like it's coming from the passenger side but that could just be my ears...

On mine the flexi joint on the down pipe completely failed, but this was a distinct exhaust noise and sounded just like a tank.

One thing I remember was the missus complaining of the engine being noises, and a a smell of exhaust. Turned out to be the grommet under the expansion tank had popped out and needed putting back. Made a massive difference in sound.

Have you checked the servo pipe, these usually crack but would effect idle. Also, the little valve on the throttle body can sometimes leak. Can't remember what I did to ours, but I didn't replace it.

Also, there is a small pipe which goes to the fuel pressure regulator in the middle, I remember I had to replace the whole pipe because it also split. It's a hard plastic pipe with tow rubber 90* bends. I used little cable ties to help them seal.

Also remember the carbon canister would wise, but can't remember doing anything to it. May be your problem. It's behind the drivers side lower bumper grille area. Can be seen from underneath.

Whatever is causing the noise, I would almost guarantee that it is NOT a vacuum leak on the inlet side of the engine.

Vacuum is at its greatest when the throttle is closed (so you you would hear a vacuum leak more when you took your foot OFF of the throttle.)

I would go along with Dixy in this, it is more likely to be from the exhaust.

Are you sure that the noise isn't caused by something other than the lack of gas-tight joints/pipes? Could it, for example, be from the auxiliary drive belt or pulleys,or even from the alternator or waterpump?

You may find that a length of soft plastic tubing, one end placed in your ear and the other moved around suspect areas, could help you to pin down the source of the noise.

Regards

On mine the flexi joint on the down pipe completely failed, but this was a distinct exhaust noise and sounded just like a tank.

One thing I remember was the missus complaining of the engine being noises, and a a smell of exhaust. Turned out to be the grommet under the expansion tank had popped out and needed putting back. Made a massive difference in sound.

Have you checked the servo pipe, these usually crack but would effect idle. Also, the little valve on the throttle body can sometimes leak. Can't remember what I did to ours, but I didn't replace it.

Also, there is a small pipe which goes to the fuel pressure regulator in the middle, I remember I had to replace the whole pipe because it also split. It's a hard plastic pipe with tow rubber 90* bends. I used little cable ties to help them seal.

Also remember the carbon canister would wise, but can't remember doing anything to it. May be your problem. It's behind the drivers side lower bumper grille area. Can be seen from underneath.

Yeah the servo pipe was one of the hoses I replaced under the hood!

Don't remember seeing a valve on the throttle body that could leak, unless you mean the main 'flap' (for want of a better word...) in the middle?

The fuel pressure regulator pipe did break as I was putting the parts back on, had to dash to Halfords to get a replacement - they had a 3.2 mm vacuum pipe in stock (for some extortionate amount) which I was able to squeeze on. Seemed a bit tight but it went on both ends okay... hopefully this won't cause any problems being a bit too tight?

Gonna pop it up on some stands and have a shimmy along the exhaust, see if I can see the problem. I'll have a look at the carbon canister as well, thanks for the tip!

Edited 8 December, 201411 yr by goldielocks

Can you take a picture of your TB and post? I think you are missing a vacuum hose at the 6 0clock position at the base of the TB. I had this too. A fairly loud hiss at idle, gets worse in revving. A vacuum hose had perished and fallen off. The one near the vacuum operated valve...

I too have the AUD engine along with Nige8021.

PoloD.

Whatever is causing the noise, I would almost guarantee that it is NOT a vacuum leak on the inlet side of the engine.

Vacuum is at its greatest when the throttle is closed (so you you would hear a vacuum leak more when you took your foot OFF of the throttle.)

I would go along with Dixy in this, it is more likely to be from the exhaust.

Are you sure that the noise isn't caused by something other than the lack of gas-tight joints/pipes? Could it, for example, be from the auxiliary drive belt or pulleys,or even from the alternator or waterpump?

You may find that a length of soft plastic tubing, one end placed in your ear and the other moved around suspect areas, could help you to pin down the source of the noise.

Regards

Aaaah okay, very interesting about the vacuum levels! So it's no surprise it hasn't fixed the problem then . Still, it's probably good for the car that I've fixed them anyway.

Now you mention it, I'm not sure it isn't something other than the exhaust, and in fact the auxiliary belt is looking a bit sorry for itself - I'm hoping to do the cambelt and water pump in the next few months and was going to do this belt at the same time. Could this belt be causing this kind of noise, which gets worse under throttle?

I do have a mechanical stethoscope somewhere that I could probably dig out... this may help! The key areas to listen to?

Can you take a picture of your TB and post? I think you are missing a vacuum hose at the 6 0clock position at the base of the TB. I had this too. A fairly loud hiss at idle, gets worse in revving. A vacuum hose had perished and fallen off. The one near the vacuum operated valve...

I too have the AUD engine along with Nige8021.

PoloD.

I can take a picture tomorrow evening and upload.

From memory though there's two vacuum pipes connected to the throttle body, one coming out at about 6 o'clock (towards the radiator) and another coming out at about 8 o'clock.

On the intake manifold there's one very thin vacuum pipe which comes out upwards and connects to the fuel pressure sensor on the fuel rail.

I think everything's in place? I can do a pic tomorrow though!

Ah that's the one! Worn water pump? Have you inspected the timing belt?

Tricky without seeing the car!

Have you tried a friendly local garage for an informal eyeball (or ear in this case?).

PoloD.

Found the picture of my inlet manifold

The Yellow pipe goes to the carbon canister valve, The blue goes to the main engine breather pipe, the bit between the red & blue is the vacuum holding valve, this was faulty on mine it's only supposed to open at a certain amount of vacuum, mine was permanently open, this was causing the epc light to come on ( no fault codes set ?) and there was a constant hiss from the valve

Found the picture of my inlet manifold

The Yellow pipe goes to the carbon canister valve, The blue goes to the main engine breather pipe, the bit between the red & blue is the vacuum holding valve, this was faulty on mine it's only supposed to open at a certain amount of vacuum, mine was permanently open, this was causing the epc light to come on ( no fault codes set ?) and there was a constant hiss from the valve

I didn't want to re-awaken the post I found this on but this picture came in very handy when I couldn't quite remember which pipes went where! So thank you for that :-)

I'll have a ganders at that valve and a close listen to see if that's at fault! We had the EPC light on intermittently since we bought the car, it's currently off, but haven't got round to getting a code reader to read the codes...

Get a vcds cable from ebay. £5 and read yourself. I use it with a netbook and win 8.1 without problem.

PoloD.

I've ordered a VCDS cable from eBay for £6, should be getting here tomorrow. Been meaning to get one for ages, as they're only £6 I thought I can't really go wrong!

Jacked the car up today and found the source of the noise, a leak half way down the exhaust. The air was coming out fairly strongly on the top (the other side) of the join in the below pic. Could feel it with the car just idling while holding my hand over it.

It was getting a bit rainy and I only had it on axle stands on the driveway, so took it up to my local Kwik Fit who do a free exhaust check... went armed with the info and the pic and they ramped it up, examined, and said it looked like it had been improperly installed at some point and this had caused there to be a gap at this joint and this was causing the leak.

They offered for £25 labour to reinstall it properly, so with a glance out to the windy rainy day, and a glance across to their free coffee machine and pile of car magazines, decided to take them up on this. Took them a good 60-90 minutes (during which I did hear something being hit with a hammer.......) and when it came out it was leak free - sounded and drove great!

This was until about a mile or two down the road, and.... it's back! Pretty much exactly the same noise. Got a slightly different tone to it, but near enough exactly the same. The exhaust was too hot and the weather too cold for me to check it myself when I got back but phoned KwikFit and booked in for them to re-fix it (or at least, take a look) on Friday morning.

Is it worth me even going back? Is it potentially something I can fix myself with just axle stands? Could it be as simple as needing a new clamp (the one in the picture)?

Thanks all for your help - really appreciated!

Edited 10 December, 201411 yr by goldielocks

Going by the soot marks in the picture it has been leaking all around that join.

If it were mine I'd disconnect the 2 sections and check the fitment between the 2 sections, should be quite a snug fit.

If the fitment seems ok I'd coat it in GunGum exhaust paste and refit with a new clamp.

Turn the car on and leave it to idle for a while so the exhaust gets hot and the GunGum has time to set.

Hopefully that will seal any gaps that remain.

The standard factor exhaust had a joining sleeve. The aftermarket ones have a flared end as in picture. When I change my centre box I ended up cutting the flared end off and reusing the joiner and hasn't leaked since. I did blow quite badly even with gum gum and a new clamp.

Being kiwikfit I'm not surprised it wasn't fixed. The second attempt will no doubt fix it as they will actually have to do it righ this seems to be the way they do things. Anywhere else I would be surprised they took an hour to refit it with a ramp and pretty much ever tool they could need. But as you said it beats messing around in the floor in the cold.

As for the valve I was referring to it's the one between the red and blue pipes above and as nige says it does fail and sounds firms liar to what I remember.

Do you have this valve fitted?

I gave Kwik-Fit another pop at fixing it, seeing as I'd already given them the £25. They spent about 2 hours with it and the result was they double clamped each end of the middle exhaust section and used a crap-load of putty... seems to have done the trick so far but I guess we'll see how long it lasts for.

They said if (I think probably when, not if) it fails again it'll be a case of replacing the middle and rear exhaust sections (apparently the rear is on the way out...) which they did a quote for at £140, including a discount of £25 to make up what I'd already paid, and they'd fit it for free... makes me laugh that the parts from eurocarparts would set me back a grand total of £40 - think I'll do it myself if it saves £100 lol. Just wrapped up warm!

Yeah I do have the valve fitted, my setup looks exactly the same as the pic from yours nige, but there's no noticeable noise from it at idle. One day I'll get the missus to rev it while I listen to see if there's anything from there, but the 'fix' of the exhaust seems to have cleared up the hissing...

Thanks all for your help along the way! As always, very helpful :-)

£140 for them to supply a pattern exhaust that will rot away to nothing in about 3 years!

I'm sure for that money you can get a stainless system off eBay.

To be honest though replacing the sections for new pattern parts can sometimes cause more issues.

I had to replace an exhaust on a Skoda Fabia for a mate. The 2 sections I bought had completely different bore sizes, like about half an inch of difference. And they were both bought from the same supplier.

Hope the Kwik Fit fix works for you now though :)