Power loss and loud pops from exhaust after changing hpfp

[Janno2G]

Hello,

I have a 05 GTI with the AXX engine. Car was tuned to about 280hp with the stock hpfp and the fuel pressure was dropping from requested value of 110bar to sometimes even as low as 55-60bar on spool followed by overboosting to the point where the turbo started surging. Today i have replaced the pump with an upgraded one from bartek along with a new cam follower. As i was driving back home from my garage i noticed the car is louder in general and extremely loud backfire and flames from my exhaust when the car is coasting below 2-2.5k rpm as well as a very noticable decrease in power and turbo is still surging on spool. Feels like it has 200-220hp at best.

Could this be atributed to the ecu being used to the loss of fuel pressure on the previous bad pump and is now just running extremely rich with lower boost or do you think the new pump is to blame?

[Janno2G]

Update: Car now doesn't start anymore

[MKVASMR]

Do a full scan. Without that it's impossible to tell you anything

[The Red Warrior]

I’ve had the same symptoms as you twice (although not the not starting bit).
Both times I’ve had petrol leaking from the HPFP into the engine.
First time it was the OEM seal that the piston runs in after upgrading to the Autotech piston and the second time it was the aftermarket seal on the part that houses the seal that the piston runs in (Integrated Engineering).
Take off engine oil cap and have a smell inside to see if it smells of petrol (it shouldn’t). To be sure you may have to drain your engine oil. If you can drain it into something clear you will be able to see the petrol separate from the oil if there is any.