A lot of discussion has gone on here about FPR's being very bad and either leaking fuel through the vacuum line or dunping inordinate amounts of fuel into the engine. Mine did neither of these. I was doing the Bosch O2 sensor tests to try to determine if my O2 sensor was good. It would respond immediately if I took off a vacuum hose at idle (air leak) but at the 2500 RPM as suggested in the test, all I ever got was a very rich reading.

I decided to replace my FPR based on this information and other posts here hoping that this would solve my fuel economy problems.

The outcome: Fuel ecomony went up 1.1 mpg to 19.2. Not exactly good economy but better then the 16.7 I got on one tank. The other outcome is - holy crap - waaay better performance. I used to get some detonation when I went into boost (even though my timing is correct and my boost is only at 5.5 psi). Now that is gone. Also, my engine would have a hard time reving beyond 5000 rpm but now that is gone as well. Overall, my car is far more responsive then ever before and I am finally starting to see a car that performs like a Turbo. All I have left to do is fix my low boost problem (and try to get more then 20 mpg on at least one tank full).

I believe what happened with my FPR was the diaphragm in it got hard and therefore 'lazy'. I think it would still increase and decrease fuel pressure somewhat but not enough to prevent too much fuel at idle and a very lean condition at boost. I just wanted to post this to suggest that this is a very simple replacement item and not very expensive. Rigging up a guage seems to be hard and you cannot tell what pressure is under boost (I don't think). WHat I did to test mine is test my O2 sensor as suggested in the FAQ. If you can only get very lean or very rich conditions and your O2 sensor does do a full sweep from .1v to .8 or .9 then you can quite likely suspect a fuel pressure regulator.

Hope this can help someone out there.