1998 pre2100wt black smoke and sluggish acceleration

[bmetz39047]

Hey guys, I need some mechanical help on my 1998 pre2100wt with a Mercruiser 350 Mag MPI ski.

I took the boat out this past weekend. On Saturday I started having some black smoke come out of the exhaust and it seemed to be running a little rough. Changed the oil and filter, put new spark plugs in, put seafoam in the oil and in the gas. When I filled up, I noticed I burned about 30% more gas (GPH) than I have been burning. Took it out Sunday it fired right up and seemed to be running great (still some black smoke). We did a little surfing then stopped, drained the fat sacs and shut off the boat. When we were ready to go again it fired right up but my acceleration was very sluggish; as in, I had the throttle all the way down and was barely going 5mph. It would eventually get up to speed but each time I would slow down to an idle it would do the same thing. I'm pretty sure the fuel to air mixture in the carburetor is too rich that's why I burned a lot more fuel, but the thing looks brand new. Any suggestions? Also, I always use 100% gas no ethanol.

[ChrisSnow]

what do your plugs look like now?

sounds like its running rather rich. EDIT, reread you have MPI...

you could have an injector that isnt closign up

[bmetz39047]

Your saying the new plugs? Should I take one out and look at it?

[ChrisSnow]

yes. take them all out but keep note of which is which(super important!). then take a photo for us of the tips :-)

the colour\condition will give away what's going on, be it all cylinders or just one.

[ChrisSnow]

also you talk about a carburettor but then say MPI? to me MPI means injection and you wont have a carb.

[boatwakes]

Bmetz, change both the ect and mat (engine coolant temp sensor and manifold air temp sensor). The two combined tell the ecm how long to make the pulse width for the injectors. You can scan to verify one or the other is reading the wrong temp but still within parameters of the engine ($100 scan, plus parts $150 or both parts for $100). Ect 805218T and mat 805223T.

[bmetz39047]

Yes chrissnow it is MPI but I did not know what that meant, I just assumed it had a carburetor. Thank you for the clarification!!

Thank you boatwakes I will try that out. It would be great if it's just a couple of sensors. Can these be hooked up to a regular OBD2 scanner or is there a specific marine scanner I need? I know its a GM block but I didn't know if an automotive scanner would work.

[bmetz39047]

Also boatwakes are those the exact part numbers for my specific engine and year?

[ChrisSnow]

Did you manage to pull the plugs? You should be able to test the sensors with a multimeter.

Sent from my HTC One_M8 using Tapatalk

[boatwakes]

The sensors are responsible for the overfueling. Post your serial number so I can verify you have a mat sensor but you should, serials after OL304000 all had them. Yes, those are mercruiser specific part numbers for that engine. Common issue, we replace them a bunch. Diagnostic scanner has to have marine efi software to properly scan and the dtc port is not an obd connector but you can scan if you have the adapters.

[bmetz39047]

I haven't pulled the plugs yet, I wasn't able to do anything with it today.

My SN is earlier than that, mine is 0L009026. According to a wiring diagram I found it does have the ma sensor. Those sensors are cheap, I will order them and hope that's it. I will keep y'all posted. Thank you for the help.

[boatwakes]

You have a map sensor only not a mat(manifold air temp) so just replace the ect and that will solve the issue.

[skyski_tige]

My 1997 2150i was running sluggish and ended up being the fuel pump.

[bmetz39047]

Alright so I took the boat out today. Still burning rich and getting black smoke after changing both of the sensors. But I have good top end now and much better acceleration (runs great at top end very smooth and sounds good). However, my low end is still no good. ESPECIALLY if I have the fat sacs full and pulling up a surfer...it takes a long time just to get up to 9-10 mph and runs rough the whole time. Whenever I changed the spark plugs I did not check the gap. A buddy of mine said they may be gapped wrong. Any suggestions on what might still be wrong? Is there a way to test the fuel pump skyski_tige or did you just buy a new one?

[skyski_tige]

I tried a bunch of things and then after a season of screwing with it took it to a repair shop. They told me it was the fuel pump.