This is a bit of a difficult 1 to answer im sure but I need to know how the fuel pressure is regulated on an X18XE1 engine. I have transplanted this engine into my 1.4 Astra. All is running perfect except for some fuel problems. My old 1.4 engine used a return pipe from the end of my fuel rail to the tank to relieve pressure on the fuel pump when my car is idling or whenever I have my foot off the accelerator. It also had a fuel pressure regulator connected to a vacumn so that whenever the accelerator was pressed the vacumn would increase and the regulator would hold back more fuel pressure and the car would pull clean and evenly. I think the standard fuel regulator was set for 2.2 bar pressure on low vacumn and 2.8-3.0 bar pressure on full vacumn, IE when accelerating. The problem is that my 1.8 engine I transplanted does not use a fuel return back to the tank or a vacumn controlled pressure regulator. There is only a single fuel feed from the pump. So how is the pressure regulated when the car is idling? Surely the pump does not stay under full pressure when idling as this would result in a rich fuel mix and high emissions, not to mention unnecessary stresson the pump. Does the ECU control the speed of the fuel pump, If so will any standard fuel pump work (I have a very good fuel pump from a 2 litre Subaru Imprezza). I have tried using my 1.4 pump but as there is no flow back to the tank when I am idling in traffic there is no regulation on the fuel pressure and the 1.4 pump soon finds itself under alot of stress and cutting out. Not good for that quick escape from traffic lights. The Subaru pump I have also uses a return so my 1.8 fuel line setup probably wouldn't suit this pump either. What pressure do oem 1.8 fuel pumps work at? Are they a specific design of fuel pump? Sorry for all the questions but when you gotta ask, you gotta ask. Cheers peeps..