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Loud hiss when turbo cuts in


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#1 rallyman

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Posted 15 June 2019 - 12:28 PM

Hi Guys, this is a strange problem!

 

I have a 55 plate 2.0 TDCI Ghia 115ps (120,000 miles). During acceleration, when the turbo cuts in at about 2000rpm, I get a loud "hiss" from under the bonnet. It sounds like a lot of compressed air leaking out of somewhere.

 

I have checked as many pipes and clips that I can see under the bonnet and underneath with the under tray removed, but cannot find any evidence of leaks.

It has a new exhaust system and with the engine on tickover, block the tailpipe with a rag and it builds up a lot of pressure without any leaks.

 

The noise does not happen by just revving the engine while stationary, only when it is under acceleration load. There is no loss of power and the fuel consumption is not affected also no smoke from the exhaust.

The car is standard spec but I sound like a boy racer with a dump valve fitted but I only get the noise when I put my foot down, not on lift off.

 

Any suggestions would be welcome! 



#2 Mondygeek

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Posted 15 June 2019 - 01:46 PM

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My bet would be the intercooler. I'm only saying this as I had the exact same issue. Much more noticeable on a country lane with hedges to reflect the sound. My intercooler had split along the top but I noticed a very slight oil patch on the intercooler
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#3 rallyman

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Posted 15 June 2019 - 03:44 PM

Hi Ben.

 

The intercooler is one item that I have not checked in detail as the front bumper has to come off. I cannot see any oil stain but it is not very visible through the front grille.

I don't know if my local garage would be able to verify a leak via an OBD II code reader?

 

So thanks for your input, as you have had the same problem, it looks like the right answer.

 

Cheers,

 

Bryan.



#4 Mondygeek

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Posted 15 June 2019 - 04:57 PM

Hi Ben.

The intercooler is one item that I have not checked in detail as the front bumper has to come off. I cannot see any oil stain but it is not very visible through the front grille.
I don't know if my local garage would be able to verify a leak via an OBD II code reader?

So thanks for your input, as you have had the same problem, it looks like the right answer.

Cheers,

Bryan.


Luckily I didn't need to remove my bumper at any stage. Managed to diagnose it using a torch through the grill, don't get me wrong it wasn't immediately obvious. I picked up a replacement for £15 from a breakers and replaced it from under the car with a few scratches on my arms but it wasn't a bad job. A garage won't be able to diagnose it with a obd code reader it will have to be pressure tested.

#5 rallyman

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Posted 15 June 2019 - 05:04 PM

Hello again,

 

Thanks again for the extra info, I hope that it will last until after my holiday, towing a caravan!!



#6 nicam49

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Posted 15 June 2019 - 10:40 PM

Hi, it could well be a split in the pipe from the air filter box to the turbo. Most likely spot is under the clamp onto the turbo.
<p><p>nicam49 2002 Mondeo TDCi Ghia X Estate mk3 pre facelift Stardust Silver+Rust.[b] 308,000+miles, but been off the road since Nov 2019 after timing chain slipped during fuel pump transplant. Awaiting return of mojo

#7 rallyman

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Posted 02 July 2019 - 10:59 PM

Convinced that I had a split intercooler so bought a new one £87 and fitted it. Made no difference, still had noise!
Took off and examined every pipe from the turbo working back to the egr valve. Finally found a small split at the back of the rubber hose just below the egr valve. Bought a new one £37 JOB DONE!
All the power is back and no noise. The new intercooler seems to give better breathing for the engine and seems smoother so not all wasted money!
Thanks for all your help and comments guys.
Cheers.
Bryan.




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