Looking at a Mercury part # 861721T2 ecu, with a label ECB4 from a 1999 454mag, is this a Mefi 4?

I've done some searching here on OSO and I see that the recommendation is to go with a Mefi 4.

It is a mefi 3. I think I know someone that has one available if you are looking for one.

Are you looking to upgrade or just replace? The ECB4 is the programing code.

I've got 94 carb 454's right now and looking at complete mpi setup someone took off a 99 454 mag. Again, I think everyone says to go with the mefi 4, so want to be sure I know what I would be buying.

Mercruiser never used MEFI 4. They went from MEFI 3 to ECM/PCM555.

Dave

The MEFI 1 has the connections on the small sides of the computer, 180 degrees apart. The MEFI 3 has both plugs facing the same direction on the same wide surface. I am not aware of them using the 2. The 4 as stated above was never used. There is a plug that Merc has came up with to connect to a MEFI4. I hear Merc has no more 3's and are selling 4's as replacements.

Looks like it's a mefi 3. Thanks for the descriptions!

Intake Manifold; Intake Plenum ;Injectors ,Throttle Body Assembly, ecu, wiring harness and I'll need an electric fuel pump. What else do I need?

Sending units of any kind?

You will need a coolant sensor, Knock sensor, and the intake air temp sensor. We have a bunch of take off parts around if you need them.

Is there any difference in the main plug on the wiring harness for the 99 compared to my 94 setup??? Or will it plug right in??