Re: poor fuel pressure on mpi 502. advise?
Your engine is covered in merc service manual #23, I highly suggest you get this manual from your merc dealer. From what I can tell, your regulater is in the cool fuel unit. Some of the early versions of this engine still had a regulator on the fuel rail on top of the engine, but it is not connected and serves no function.<br />I have to repeat my original post that fuel pump problems were common.....don't rush into thinking it's the regulator. Something in your original post also has me skeptical that it is the regulator (" I can't get the pump to cycle with the turn of the key"). That engine has the MEFI3 ECM, it sends a signal to the pump relay everytime the key is turned on (regarless of pressure). If you are not getting a running pump when you turn on the key....it could be the pump relay, the wiring, the pump...or lastly the ECM(possible, but highly unlikely). If you still want to rule out the pressure regulator, remove the cover from the cool fuel unit (it's plastic and has tabs that snap it in place). locate the braided hose that comes off the front of the regulator (top component in the unit, the fuel pump and fuel supply line are in the bottom). Pinch off that top hose, if the pressure goes up....it is most likely the regulator, if no real change in pressure....time to start troubleshooting. You had asked if you could pinch off the return line at the water seperator....yes, if you can tell which one it is (there should be 3). If you can locate the one from the fuel tank, the return line should be directly opposite of it and the fuel supply to the pump next to the return line. Keep us posted on your progress.
