I have twin Mercruiser 502 Magnum MPI's (2000) and my question is this: Does the MEFI 3 ECU measure and use fuel pressure? Can I use the signal to display the pressure on dash gauges? If not, where would I mount a sender to measure fuel pressure?

There is no transducer to tell computer actual fuel pressure. The best place that i know of would be to remove the brass pipe plug in rear of fuel rail (near distributer) and install a tight 90 dgeree fitting with a sending unit,Smitty

MEFI 3 systems do have the ability to connect to a fuel pressure sensor, but none were ever installed on the 502's, or anything else as far as I am aware.

I have installed Gaffrig fuel pressure gauges by extending the fitting at the front of the fuel rail, and "T"ing in the sender with the schrader valve. I have a picture somewhere, if you want I will find it and post.

Dave