The fuel pressure regualtor uses a pulse width modulated wave so you won't be able to see much except check the live. The earth is what is modulated through the pin on the ECU as in this diagram. This helped a guy with a similar problem not long ago, turned out the relay was faulty IIRC.
http://www.hdi-tuning.co.uk/downloads/edc15c2pinout.jpg
http://www.hdi-tuning.co.uk/downloads/edc15c2pinout.jpg