I am going to be installing a fuel pressure gauge on a 7.4 mpi (1999) and I need help with where to plumb the sender. There is a service port (shrader valve) on the front of the motor by the intake manifold and that looks looks a good place. Has any one ever done this? does anyone know where I can find a fitting/ adapter to utilize this valve for a sender? any help would be appreciated...

Here is some info from Mercruiser about fuel pressure gages and hookups. Not sure if it applies to what you are doing, but maybe. This is from a factory service bulletin, with Merc part #'s. Hope this helps...

Fuel Pressure Gauge Kit
1998 MCM/MIE 7.4L MPI uses a different size and type of ‘test port’ valve on it for checking the fuel pressure at the fuel rail. The current Fuel Pressure Gauge Kit (P/N 91-16850A 2) will not attach to this valve. A new kit is superseding this kit and it will contain 2 fittings so it will fit both types of ‘test ports’ and a TBI pressure valve to allow the gauge to connect to TBI engines. Quicksilver will also sell an Adaptor Kit that can be purchased to update the older 91-16850A 2 kit. This kit comes with both size ’test port’ valve adapters and instructions on how to fit it to the older gauge kit.

91-16850A 3 Fuel Pressure Gauge Kit. Kit contains Adaptor Kit and TBI Pressure Valve.

To update older 91-16850A 1 or A 2 Fuel Pressure Gauge Kit, order the following.

91-806901 TBI Pressure Valve. Allows older Gauge Kits to connect to TBI engines.

91-803135 Adaptor Kit. Allows older Gauge Kits to connect to either type of ‘test port’
valve.