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Vacuum leak...?


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Hello all,

I posted a while back about a vacuum leak on my a3 in the a3/s3 section but alas no one replied, thought Id try again in this forum.

Original post:

Hello everyone,

My 2001 150bhp a3 1.8t has developed a yellow CEL on the dash. I checked it a while back using VAGCOM and it reporting a system too lean fault along with turbo pressure drop between turbo and intake fault. I checked the fuel trim settings on group 32 and they were reading -5.6% additive and ~6% mutliplicative (idle and load values respectively).

I think I have fixed the latter fault by checking the pipes leading into the pancake pipe and into the intercooler and having not found any splits putting them all back on (would appear to have inadvertantly fixed the loose fit or whatever that was causing the boost leak). So looks like its not leaking any more boost.

Im still having problems with the vacuum leak though and as you all know there are many pipes that comprise the vacuum system on one of these engines (its an AUM by the way)

I bought a forge intake pipe to replace the stock one, but having tried unsuccessfully to fit the forge tip (couldnt get the damn forge pipe down and onto the turbo itself, as other gubbins where in the way and the stock pipe one has a narrower metal section at this point) I didnt see any splits or holes in the original pipe so have for the moment replaced the original pipe back on.

(any advice as to how to replace the stock intake pipe with a forge one?? without having to remove the exhaust manifold!!!, should I try greasing the outside of the pipe... to get it through the tight space and onto the turbo...??)

Ive had a good look at the oil breather hoses too, replaced the y shaped oil breather hose that connects to the top of the camshaft case, (which did have a hole in it, but the 'system too lean' fault still persists and havent been able to find any other splits/tears or holes...

Do any of you good folks know where the usual place for a hole or tear to appear would be? Which pipe should I check? By the way I have checked the DV (its a stainless steel replacement for the stock one) and the bypass pipe from after the turbo that feeds it, they're all ok.

I have thought about replacing the pre-cat lambda/o2 sensor but nothing comes up in vagcom regarding the o2 sensor... Just thought it might have been contaminated and is reading bad oxygen levels...

Im a little stuck now what and where to check, would love to be able to solve this for myself. Any help/advice would be very much appreciated.

Cheers in advance...

Any help would be really appreciated...+++

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  • 2 weeks later...

Hi there. Most likely issue is that the suction-jet-pump and it's non return valve are leaking. If you look beneath the inlet manifold you will see it. It has a hose from the inlet and it looks like a black funnel type thing! About 3" in length. It creates a vacuum for the brakes even while the engine's on boost. It has a non return valve inline to and both start to break down after a few years of heat exposure. If you remove it you'll be able to suck and blow through it, where as it should be one way! I think a new whole thing (def need both vac suction pump AND non return valve) comes to around £30.

I can try to find some images of the area if it helps you identify it. I'd put a tenner on it being that tho!!!

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Thanks for the pointer,

I took a look at those pipes youve mentioned before, but because if their location they're a pig to get at properly so I didnt notice a nice split running underneath one of the pipes.

I got a new replacement pipe and tried fitting it saturday. Oh my ! they do make these pipes out of putty, blimmin Audi/VW cost cutting:ffs: The large pipe running into the top of the oil filter housing broke in half along with other smaller pipes splitting apart like they were made from paper!!! :eek: Its Saturday afternoon, all the audi/vw dealers are closed. I was really stuck!

But then I thought sod it Im going to jury rig something together. Off to homebase I went and got me some garden hose and pvc tubing and lots of hose clamps. Took me the rest of Saturday but I managed to replace the broken audi/vw stock hoses with white pvs tubing and garden hose.

Cant believe it but my car is running better than ever, I cleared the boost leak fault code and it hasnt come back since saturday! :))) So Ive definately found the culprit. New genuine replacement hoses have already been ordered. Thanks again for your help BM2309. +++

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