I have a 2000 Mercruiser 350 mag MPI inboard that has began acting up and I believe it is the ECM. It is has the MEFI 3 installed and I understand these are no longer available. From looking through the various posts it appears that the MEFI 4b is a suitable replacement with a pinout change or an adapter harness.

Symptom:
I have been having intermittent electrical issues with the fuel pump. When exhibited the boat will go from running like a top to running extremely rich for a few minutes then shut down all together. At which point it won't spin up the fuel pump unless I unplug either j1 or j2 from the ecm at which point it sometimes corrects the problem for a brief period (2-5 minutes) and then does it all over again.

Does my assessment seem to be correct and if so I'm looking for suggestion on where to find an appropriate replacement ECM for this engine, and what if any considerations do I need to be aware of.

I'm in Kansas City and we don't appear to have any dealers that will even touch an inboard engine in the vacinity. Any help someone can provide would be greatly appreciated.

its not your ecm. did you check all your grounds? how about the fuel pump relay? try replacing it first...its cheaper. did you check your fuel injectors for approx 15.7 ohms ... yes opened or shorted fuel injectors will cause a rich condition. pull off the conectors to the fuel injectors and measure it there. make sure they are all above 15 ohms, repalce the ones that are not

Thanks for the advice Larry, I did as you suggested.

At this point I have checked all ground connections, the positive connections, the fuel injectors, all sensor connections and the main connection between the "power" harness and the "ECM" harness. I am currently not really having any luck getting the system to even power up. One in about twenty attempts will result in the system firing up for about two seconds, but then it will shut back down and the CodeMate tester will light solid. The thing that seems to get this to work is pulling the J2 connector and then reconnecting it.

I have "wiggle" tested everything I can think of, and have pulled all wire tape and wire wrapping off the harness to expose all the wires for ease of "wiggle" testing. At one point it seemed that wiggling some wires on the J2 connector kicked the system on but it was completely intermittent so I wasn't able to locate a particular wire and now it doesn't do it anymore.

Electrical problems are the worst. Is there another method to check the ECM to make sure it's powering up properly? The CodeMate tester simply stays on and the fuel pump won't spin up. I can't help but think I should be able to use a test light on a certain wire and get a response, but I don't want to just go checking any wire for fear of blowing the ECM. Does anyopne know if this is possible and if so which wires would be safe to check in this fashion?

Any further advice on what to try next would be greatly appreciated.

Mefi 3 ecms are still floating around...

Give Bob a call @ MEFI Burn, http://www.mefiburn.com/ 310-793-2410

Turns out Larry was right. It seems to have been the fuel pressure sensor. After completely pulling the wire harness apart and following the Throttle position sensor wire down to the Fuel pressure sensor I finally located the problem. For now it is running like a top again.

Electrical problems === frustration.

Thanks for all the suggestions and information.