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I have a 1997 GTI fitted with a VR6 turbo.
The problem im having is that fuel pressure will drop off when going into boost and the car runs lean. the fuel pressure will start to rise with boost and then fall off drastically.
It has a brand new factory in tank fuel pump feeding a bosch 044 pump with factory fuel lines all the way up to the rail.
The rail is an aftermarket rail with a fuel pressure regulator adapter that holds a factory fuel pressure regulator.
The car is currently only running 15 pounds of boost.
Things i've tried.. Replaced the in tank pump with another new pump.
Replaced the bosch 044 with another new 044 pump.
Replaced the fuel pressure regulator.
Swapped out to an entirely different adjustable fuel pressure regulator.
Removed the fuel lines from the car and inspected for any kinks or damage.
Replaced the fuel filter. (Factory OEM filter)
Checked and replaced the vacuum source going to the fuel pressure regulator.
The 044 pump is at 13 volts all the time, but i thought these pumps were tested at 12.5volts. I could be wrong though.
Im at a loss here. This is the same set up i've run on many cars in the past without an issue.
Clearly im missing something and any help would be awesome.
It sounds like there is a restriction in a line if pressure comes up then falls of with higher demand.
Have you tried reverse flushing the lines with compressed air?
Is there any soft line that can collapse on either pump suction?
Thanks for the reply!
Checked all the hoses for any blockage and didn't find any.
Replaced the feed line from the pump to the rail with a -6 hose and that didn't change anything.
Installed an integrated engineering surge tank with the 044 and that fixed the problem.
I can only assume the intank pump was not able to flow enough fuel to the 044.
I had a similar issue with a mk6 GOLF R. It was the high pressure fuel pump. Upgraded it to Loba and afr is stable after that...