I've always had mixed feelings about this mod. Talked to my Opel mechanic about this. He was also interested in finding out how this works. Connecting the fuelpressure regulator to the manifold is the way lots of engines work. However, more modern engines sometimes use static fuel pressure. Depends on how the ECU is programmed.
So Leo (the Opel mechanic) mailed me yesterday that he just had to find out, and he did some measurements on a Speedster they have. He sent me some pictures of what he did. First the test setup:
After warming up the engine he connected a Tech2 to the engine to watch the fuel adjustment, he connected a vacuum/pressure pump to the fuel pressure regulator and a pressure gauge to the fuel rail.
So first up the let the fpr just have atmospheric pressure, so what you would almost have when the fpr is connected in the default way.
As you can see the fuel pressure is around 3.8 bar. He also changed the revs of the engine, and the fuel pressure remained the same. So we can safely assume that this engine is mapped for static fuel pressure. The Tech2 showed the normal values for fuel trim, 3-5%.
Next up was to apply vacuum to the fpr. This is the result:
So fuel pressure has dropped to 3.2 bar with close to vacuum on the fpr. So this seems to be a normal fpr, it gives lower fuel pressure when connected to vacuum. Also, the Tech2 showed a major increase in fuel trim, it was adding up to 19% on the short term trim. So that confirms lack of fuel.
So unless I'm missing something, I think Leo has prooven that this isn't a very interesting mod..
Mark