Hi guys, still have a problem that my car doesn't want to make boost.
Compression is good (average 115psi on all faces), this is on a S5.
When I look at the fuel pressure gauge it's 38psi with ignition on, 32 psi @ idle and rises to 38psi when I open the trottle lightly, but when I want to make boost it just doens't rise. So what fuel pressure do you see when boosting?

 

In general, for each rise in boost you should be getting a one lb rise in fuel pressure. Like if I'm doing 10psi of boost, I get around 49-50 psi on the fuel.

IF your driving along and put the pedal down and the vacuum gauge reads zero, you should see 37-39 psi on the fuel gauge.

Idle your car and go to the FPR and pull the vacuum line off and make sure it's pulling vacuum.

Then again maybe you have your FPR vac line going to a source other than what it should be.

Try something different. Tee in a vac line to the bov line or boost line and run it to the FPR. Then go for a ride to see if things changed.

It sounds a lot like you don't have the FPR vac line going where it should right now.

 

the vacuum diagram is not at all clear, and i see the fuel pressure regulator line wrong a lot (done it myself!).

the holes in the rear of the intake are NOT the same. if you get the wrong one, the FPR does not see boost, so its lean under boost.

its very easy to pop the line of at both ends and make sure its right

 

Thanks guys, will try it.