502 mpi adjustable fuel pressure regulator
 

Does any one have excpience with this, how hard is the install? Can anyone explain it? I've installed headers and flame arrestor and I think I can avoid having my ecu done by doing this

You should have a regulator under the cooler housing cover:

http://www.mercruiserparts.com/Show_...ND+FUEL+COOLER

See the above. You'll need to remove the stock regulator and install an adapter fitting. I'll look up the part number. Once this is done, you can now install a different regulator, remember you want the regulator located high and close to the fuel rail.

What year engine do you have?

Here's one such regulator to replace the stock one:

Part No.: 620-15529
Hardin Marine Adjustable EFI/MPI Regulator for Late Model Mercruiser.

List Price: $69.95


http://www.cpperformance.com/

Vortec
 

Vortec sells the same similar type. Good info on their site:

http://www.vortechsuperchargers.com/...ptimizers.html

If you up the pressure more than six or seven psi, then you may need to upgrade your fuel pump. By all means put a fuel pressure gauge on the system so you can verify full pressure at WOT.

Its a 1999 502 mag mpi

I have the same situation as you do. Only with a '99 454 Magnum. I changed the exhaust, flame arrestor and added MSD6M-2 to the ignition. Last season, the plugs were a touch leaner than I would like them to be. Over the winter, I picked up a Vortech adjustable fuel regulator. I haven't put it on yet, but it seems easy. All you have to do is remove the stock regulator, cut the top off, and add on the new adjustable top. BUT, on my boat, I think I will be removing the entire fuel pump. It seeems easier than screwing around hanging upside down in the bilge. I also added a mechanical pressure guage to the back of the fuel rail. I want to monitor the pressure. Another reason for not putting the adjustable regulator on yet is because I want to get an accurate pressure reading with the old regulator before I modify it. When I start the motor in the spring, I'll get the readings and then put on the adjustable regulator.

Better to install a mechanical gauge in your panel than on the back of the rail.