Boost leak, what could it be?

LeonL · August 26, 2009, 08:41:58 PM

Hi,

My car doesnt seem to be down on power, however i get a whistling noise coming from under my bonnet while accelerating which i can only assume is a boost leak. The noise only happens when i put my foot down and doesnt happen every time. Its abit random, seems to do it less as the engine gets warmer/used? The noise is a whistling and is sometimes quite, sometimes loud.

I have narrowed it down to somewere inside the red circle. I have already replaced the long bending plastic pipe trying to solve this problem. I'm pretty certain it comes from this area but cant be 100% sure,

I have checked the boost pipe connected to solid plastic pipe i replaced many times and cant see anything wrong with it.

Any ideas were the leak could be? Is it even a leak at all?

Thanks

Leon

PS: Engine picture was found on google, sorry if its yours!

LeonL · August 26, 2009, 09:17:10 PM

The noise seems to be alot further forward to the front of the bay then the CO2 Pot.

G40supercharged · August 27, 2009, 01:23:33 PM

The corrugated hose that comes off the bottom of the supercharger may have a small hole in it. This hose tends to deteriorate and gets cracks in that are normally OK but open up under boost. Had this on mine and it made a squealing noise when boosting.

I did a temporary fix on mine by wrapping some black electrical insulation tape round the hose. This lasted a while until the thing split apart completely. Genuine hose from VW is around £100!

LeonL · August 27, 2009, 05:46:02 PM

I have checked all boost hoses and they all seem fine though

LeonL · August 28, 2009, 05:58:23 PM

Quote from: Rae on August 28, 2009, 09:04:56 AM
Quote from: LeonL on August 27, 2009, 05:46:02 PM
I have checked all boost hoses and they all seem fine though

did you do what i said about the flap trick to check for leaks?

Couldnt quite understand what u meant by the "boot flap thing" lol

Edit:

Had a good look at my CO Pot today after rae mentioned it. I noticed mine looks a little different so took a look at a few G40 engine pictures and it appears the "cap?" has been pushed in a fair way on mine....? It also looks a little battered. Could this be a problem? Why would this have been altered? Solution?

Here are some pictures of mine:

G40supercharged · August 28, 2009, 06:45:51 PM

There should be an O ring inside the plastic boost pipe where the CO pot fits into it. Worth a check that is in good condition and fitted properly. The CO adjustment (circular bit at the top) is just a potentiometer on the back of the circuit board inside the unit. This should have no connection to the air at all. The air temperature sensor is the only bit in the airflow. There is a blue cover missing from the top; this is just an anti tamper cover to stop people spoiling the emissions settings. I don't think it seals anything up.

'Boost flap' thing is just inside the outlet (smaller diameter) side of the throttle body. This blocks the outlet to stop the boost air recirculating when at full throttle. The operating lever for this is coupled to the main throttle plate by a rod with plastic ball joints at each end. By (carefully!) disconnecting one end of the rod you can close the flap and force full boost at any throttle setting. This will let you hear any leaks more easily. As said previously best not to force full boost like this for too long.

LeonL · August 28, 2009, 11:26:45 PM

Mine doesnt have a blue cap?

The rubber ring that seals the pipe is fine as i played with this before i replaced the pipe. The noise was happening before and after this so doubt its that

LeonL · August 29, 2009, 08:29:34 PM

Just replaced the rubber boost pipe with a brand new one, still no difference in the sound i can sometimes hear

Checked boostage on boost gauge and it doesnt seem to be losing any boost either...Very strange

GR40 · September 27, 2009, 08:44:55 AM

there is a small pipe that connects to the plastic one under the pipe close to where the CO pot fits! is that on? I had forgotten mine out once or twice! it could also be broken there or somewhere further down! just a thought!

LeonL · September 27, 2009, 10:21:19 AM

Quote from: GR40 on September 27, 2009, 08:44:55 AM
there is a small pipe that connects to the plastic one under the pipe close to where the CO pot fits! is that on? I had forgotten mine out once or twice! it could also be broken there or somewhere further down! just a thought!

Hmmm i'll check that out today

Cheers