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Author Topic: Mk5 GTI Boost issue - Help please!  (Read 277 times)

Offline FlashGTI

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Mk5 GTI Boost issue - Help please!
« on: July 07, 2022, 05:32:07 pm »
Hi all, I have a 2005 MK5 GTI and I am having a boost issue at present

When Boosting it will boost hard but  as it gets over around 1.1-1.2 bar it drops straight off to about 0.2 and you can hear a pressure release. The car will keep accelerating but just no boost.

If I drive the car looking at the boost gauge and keep it at 1 bar boost pressure then it will keep accelerating like like without the drop off.
So I have to use only half the accelerator to have the boost pressure! I think this does it in all gears when driving it today.

No codes and no lights on the dash.
This all started when I had a turbo fitted a few months back so thought it was a faulty turbo/actuator, but now  the turbo has just been changed again to a newly refurbished turbo from turbo active and just been fully refurbished I.e fitted last week and was like this with the previous turbo too.
Was stage 2 mapped, now put back to stage 1 today and  it’s the same still!
N75 new, dv valve new, actuator came with the turbo already setup etc.

Any other ideas from anyone. This is driving me crazy!!!
There has to be some other valve, solenoid or something telling this to release pressure mid acceleration!

Offline Pudding

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Re: Mk5 GTI Boost issue - Help please!
« Reply #1 on: July 07, 2022, 07:03:12 pm »
Fuel cut?

Need to do some logging with a scan tool/VCDS.


2007 ED30 | 2009 TDI 140

Offline FlashGTI

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Re: Mk5 GTI Boost issue - Help please!
« Reply #2 on: July 07, 2022, 07:06:45 pm »
I have VCDS, to be honest though not sure how to use it properly. What would I need to log to check the fuelling?

Offline GVK

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Re: Mk5 GTI Boost issue - Help please!
« Reply #3 on: July 07, 2022, 09:00:28 pm »
Find APR's very helpful TFSI logging page online.

It gives you all relevant measuring blocks

http://www.goapr.co.uk/support/datalogging.php
« Last Edit: July 07, 2022, 09:03:46 pm by GVK »
Scirocco TDI GT---- VAG scans in South Lincs/Cambs/West Norfolk.

https://www.facebook.com/groups/gvkmotorsport

Offline JoshB

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Re: Mk5 GTI Boost issue - Help please!
« Reply #4 on: July 07, 2022, 09:13:06 pm »
Sounds like a blowing seal to me, especially if you can hear the boost being dumped. Check all you intercooler pipes, check the PCV pipes and check all the breather hoses.
Getting too old for this...

Offline FlashGTI

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Re: Mk5 GTI Boost issue - Help please!
« Reply #5 on: July 07, 2022, 09:37:41 pm »
Ok thanks for the advice. I will have a look through the hoses. There is one big hose between the fan and the front of the Engine that the fan has been rubbing against quite a lot by the look of it. And there is some sort of sensor right by that rubbing too.
So maybe that could do with changing

Offline Pudding

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Re: Mk5 GTI Boost issue - Help please!
« Reply #6 on: July 08, 2022, 05:42:02 pm »
I have VCDS, to be honest though not sure how to use it properly. What would I need to log to check the fuelling?

I keep meaning to do a step-by-step VCDS logging guide but it's pretty straight forward.

You want the 'Advanced measuring IDs' within the '01 Engine' controller.  You can log up to 12 items at once and save it to a csv file for reviewing at home.

The key ones are fuel pressure 'Current' which is your in-tank pump and 'Fuel Rail (specified)' and 'Fuel Rail (Actual]) and to make things easier, 'Fuel Rail - difference'.

You might also want to log 'Throttle valve angle' in case the ECU is shutting it.

It could be also leaking boost pipe O ring as mentioned, so check all that stuff first.



2007 ED30 | 2009 TDI 140

Offline FlashGTI

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Re: Mk5 GTI Boost issue - Help please!
« Reply #7 on: August 02, 2022, 07:17:45 pm »
@Pudding I finally got round to logging some data as you suggested. what should I be looking for on the CSV file.
The trouble is I couldn't accelerate through the gears hard due to the road I was on on was narrow so was on and off the throttle.