So after almost 3 years not owning a MK5 GTI.
I could not resist and 3 weeks ago I acquired another Mk5 GTI, only in DSG this time.
I was very happy, as the first 2 tanks of gas gave me an average of 13.8km/L on the highway and town around 10.8-11.5km/L.
For no reason of driving style I'm now averaging 5.8km/L around town and barely make 7.9km/L on the highway.
So from those fuel numbers I have gone from 580-690km per tank to 380-440kms per tank.
I have only experienced one consistent error in the whole car being overboost issue. Error message, not actual over boost as half the time car had inconsistent boost.
Since then, I replaced all the following parts to try and rectify,
Tried Factory Golf R intake as appose to FSI intake (I believe they are the same)
New airflow sensor
new front PCV, tried blocking off front PCV
Replaced both oxygen sensors
New thrust sensor on fuel pump, even tried low mileage Golf R fuel pump
New camshaft bucket
New diverter valve D and also G
New N75 (fixed overboost error message)
New spark plugs
New coil packs
Tried aftermarket intake (VWR, also made sure now fuel trim issues)
I then had the car on the Dyno today. It's running incredibly rich. Around flat line of 11ish from idle to redline
Tried both 95 and 98 octane to see if that would make a difference.
Car was at Stage 2+ when I bought the car. So none of these things have changed.
Using VCDS, shows within a few degrees of temp on cluster compared to engine sensor.
Performed an oil change and new filter as well. Using Motul 507 specific. Even tried seafoam as well.
It blew a lot of crap out the back.
Still no change however. The local VW agency just looked at the car and blamed the exhaust. Even thou it's been on the car for years. They did not appear to really know much if anything at all.
If this fuel usage issues got gradually worse over months or years I would be inclined to look into carbon build up.
However, this is only from a matter of a week or 2 at most.
If anyone has any potential ideas or possible solutions? It would be greatly appreciated.
Thanks