OVERBOOST ISSUE

JamesVAG

JamesVAG

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Hey Guys.

When I go over 80mph for a set period of time car will go into limp mode then have to pull onto hard shoulder and restart car. Scanned with Vagcom and comes back with an over boost error code. Been doing loads of research and most places are saying it could be one of the following:

sticking turbo veins.
N75 valve
maf sensor
map sensor
pipe leakage

Not sure what to try first.

Power wise there are no problems at all, however the turbo does make the police siren noise.
I certainly don't have any money for a turbo replacement.
Some people a recommending:

Forte Diesel Turbo cleaner.
Mr Muscle fix

Anyone had any experience with this issue.

Thanks
 
Last edited:
If it's over boost then it's not going to be a boost leak or a MAF problem. If you have VAG-COM you can log the boost readings and see whether the MAP sensor is reporting correct values. When the MAP sensors fail they usually report max boost all the time so check to see it's reporting atmospheric pressure at idle. If you are seeing 1.6 or 2 bars of boost st idle the MAP sensor is faulty.
The problem is usually due to the N75 being faulty or turbo vanes clogging up though.
If the turbo is howling then I would sort it asap to avoid any further damage to the turbo. They go into limp mode to protect the turbo so until you resolve the issue I would keep the revs down.
 
desertstorm said:
If it's over boost then it's not going to be a boost leak or a MAF problem. If you have VAG-COM you can log the boost readings and see whether the MAP sensor is reporting correct values. When the MAP sensors fail they usually report max boost all the time so check to see it's reporting atmospheric pressure at idle. If you are seeing 1.6 or 2 bars of boost st idle the MAP sensor is faulty.
The problem is usually due to the N75 being faulty or turbo vanes clogging up though.
If the turbo is howling then I would sort it asap to avoid any further damage to the turbo. They go into limp mode to protect the turbo so until you resolve the issue I would keep the revs down.
Click to expand...

Dude thanks for your quick response. Ok have taken a few readings at idle not too sure what I'm looking at. I suppose next step is mr muscle clean and replacement N75 Valve
 
Fault
 
audi upgrades
Those readings look fine the MAP and MAF readings are what I would expect at idle . Mr muscle is only a temporary fix if it works as it doesn't fully clean the mechanism. It could be the N75. You could try disconnecting the vacuum pipe from the actuator and plug it. take it for a drive and log the specified and actual. If it still overboosts the VNT is clogged.It will probably be sluggish at the bottom end with the actuator disconnected.
 
Innotec is the best cleaner, been used for years on all kinds of VAG turbo cars. The noise you describe doesn't sound good.
 
The whistling / siren noise can be because the vanes are not open enough on the turbo, this causes the exhaust gas to accelerate to high speeds through the VNT mechanism and essentially plays a tune. This causes the turbine to overspeed and eventually the turbo fails a lot sooner than it should have.
All the various cleaners are just band aids as the only way to clear all the baked carbon from the VNT is removal and stripping of the turbo.
 
had the same problem with my b7 sticking veins,you could try the mr muscle, but it will be a new turbo in the end
 
Hello chaps.

I have attempted the Mr muscle fix today. Unbolted cat from side of turbo felt Inside and there was no play with the unit inside the turbo and so I pumped in Mr muscle, tried to get it in as far as possible. Left in for 2 hours whilst moving the actuator rod every 15 minutes. Assembled everything back together. Took it out for a test drive however now I new noise has developed that I've never heard before. When the turbo kicks in at about 2500rpm there is a loud high pitched whistling. I knew the turbo might not be in the best condition but I didn't expect the Mr Muscle to make it worse. Any ideas guys.
Thanks
 
Like its been said the mr muscle mod is just a temp thing,the only way round your problem is new or recon turbo,as i said i had the exact same problem
whistling and lots of power when on boost,diagnosed as cracked and sticking viens so had no choice but replace it with a new 1 total cost inc fitting 900 quid, 3 weeks later i had the oil pump mod done another 600 quid,once these cars start its never ending,4 weeks after i had it all done i got shut of it and went back to mercs,can honestly say wouldnt buy another audi.
 
my 2005 Audi A3 2.0l sport tdi has developed a loud whistling noise, any advice guys as i'm reading conflicting reviews as to what the fault could be, i have removed the intake pipes and cant see any splits but there seems to be a lot of movement in the pipe joints.
 
i had same problem on my a4 2tdi b7 i ended up reading load and gettin worried i would end up with a big bill but i have put a few bottle of redex in tank when almost empty and sprayed a couple of can of egr clean into air intake pipe and ive done around 700/800 miles with no limp mode or overboost problem may onlu be a temp fix but has wok for me
 
Your right usually these things are only temporary fixes and although the ECU isn't reporting issues the VNT mechanism on the car is probably not 100% working as it should.
These turbos have no wastegates and all the exhaust gas flows through the turbine. If the VNT is unable to open fully then the turbo overspeeds. This very much shortens the life of the turbo. It also reduces fuel consumption as when the VNT is fully open the back pressure produced by the turbo is greatly reduced. Stripping the turbo and cleaning it is the best way to clean it. Squirting chemicals in there will probably dissolve some of the carbon but it can't clean the entire mechanism so it may not be be going into limp mode but will probably still not be working as it should.
 
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