I'm having some problems with my boat that the local shop can't seem to figure out and it's killing me. Anyway, boat is a 2004 Baja 232 with a 6.2 MPI. It started running really rough at idle the 3rd time out this season. I would have to give it some throttle to idle and get us back to the dock and thought it might be the fuel. Lots of soot/unburnt fuel on transom. Ran some seafoam through it, filled it up with non-ethanol and changed the fuel filter with very little improvement. I changed the plugs and distributor cap which was slightly corroded and took it out and it is still rich i.e black exhaust and soot on transom. I could barely get it back to the dock when we left the cove and it died on me a few times even backfiring. Also bogged pretty bad, couldn't get it on plane and then when I was able to get it on plane it ran great and continues to run on plane fine. Anyway, I took it in and thought it might be the IAC motor but the shop says no. They said the thermostat was stuck open so they changed it but told me the timing was off 14 degrees according to their laptop (DDT meter?) and throwing no codes. This is where it gets weird......Mercruiser told them that they think it might be a bad ECM, but after talking to some pretty smart people (smarter than me ) I am not so sure. Shop told me fuel pump and injectors are fine. My question is that some people are telling me that if the ECM is bad it will throw a code. That seems like sound reasoning. Shop told me that if the ECM is bad it might not throw a code. I told them well damnit, I can't afford to drop 1400-1800 bucks on an ECM that might be fine! Of course the ECM is non-returnable.

I guess my questions are.....how in the heck would the ECM timing get changed without being reprogrammed? Could the timing get jacked if the ECM is bad?

I might replace the MAP sensor and IAC motor anyway since I have them on hand. Any input on this is appreciated, so thanks in advance!

If it goes on Limp mode yes the timing will be at the base setting with no advance but it should not run so rich in that case.
Check your fuel regulator/pressure I'd go there. Somehow I think its a fuel pressure problem.

I thought it was a fuel problem at first too but they told me that everything looks good with the fuel system and pressure. I wish I lived closer to some good marine mechanics, but I'm out of luck in my area.

check the fuel pressure regulator,if it has a vacume line going to it and the regulator goes bad it will suck the fuel through the vacume line which will cause it to stumble and possible die..

start the engine and pull the hose off(if it has one) and see if fuel comes out of where the hose was..may want to put a rag over it because it could squirt al over the place..

I will check it out. I guess worse case scenario if it is the ECM, I can get a new one for 1000-1200 bucks.....

Any other theories are welcomed!

A bad coolant temp sensor or poor connection on it will also give you a rich condtion.

I doubt its a bad ecm, although that can certianly happen without throwing codes. It could be lots of things, you really need a good mechanic. Have the injectors been balance tested, flow tested, or even removed with the fuel rail pressurized to see if they leak? They can also be commanded on and the spray pattern inspected. Do all the plugs look the same? Compression tested? Leak down? Just remember the KISS philosophy: Keep It Simple Stupid. Check the basics before condemming an ecm.

Also charging good 14 vts. ? Good batttery also ?
ECM'S need proper voltage.

Thanks guys, I am definitely going to take it in for a second opinion. I live in central NC so there are not a lot of options for "quality" shops and mechanics around here. I may post up in a regional forum for references. Current shop uses DDT, which I hear is outdated compared to CDS.

Batteries are good, injectors need to be tested, plugs have 2 hrs on them (but I will pull them and check.)

Had the same problem on a boat once. Went thru everything, TPS, IAC, MAP Sensor, ECM check, Voltages, swap in know good parts from the other engine.......the list goes on.

Turned out to be a $20.00 temp sensor causing the ECM to tell the fuel system to dump more fuel. There are usually 2 temp sensors, one for the dash guage, and one for the ECM that monitors engine temps. The ECM sensor is the one you want to change.