Help! Engine Problems (350 MAG MPI)
 

I’m having an intermittent problem with my engine that is driving me nuts. Maybe someone here can give me some guidance. The engine is a 1997 MerCruiser MAG 350MPI Gen+ and is a multi-port fuel injected engine. It currently has about 190 hours on it.

I noticed while at AOTH III my boat had developed a very slight miss that was present while idling. The boat still ran pretty well though and had not lost any speed or power.

Last weekend out on the lake, the boat ran fine pretty much all day until we came off plane in front of an island. We had been running hard all day and while coming off plane we took a couple of good waves over the bow. When I went to power up the boat sputtered and acted like it was only running on 6 or 7 cylinders. I backed off the throttle let it idle for a moment and tried to power up again. On the second try, all was fine and the boat ran well for the ride back to the ramp.

Last Friday, we launched the boat, idled out to the lake and when I went to power up, she sputtered and did not want to go. I quickly turned around and put her back on the trailer. I looked over as much as I could in the parking lot and cannot find anything that is obvious. I went and bought a new cap and rotor and installed them at the ramp. The boat seemed to be running OK again so we launched again. This time on power up, the boat sputtered again and then it caught on and ran on all 8. We didn’t go far, but did head out to a nearby island. On the way back it was doing it again. One minute it sputters and runs like crap and the next second it will catch and run fine, then sputter, then be fine, etc.

Yesterday, I replaced the water separating fuel filter and pulled the plugs for inspection. Although nothing looks really wrong with the plugs, they do all look a tad rich as they are covered with a layer of black carbon. The plugs have always been a cardboard color when she ran well. All the plugs had the black carbon on them and no one plug looked any worse than the others. It seemed to be running better on the trailer with the new fuel filter and after running for several minutes in the driveway, I pulled a plug and it looked like it was starting to clean up and go back to tan.

We went out to the lake where the boat ran fine on the way out to the sandbar, but on the way back began missing and sputtering again. I’m lost. The plug wires look fine, but I will be buying a new set just in case.

Does anyone have a clue as to what is going on? Can a Merc mechanic plug into this engine for diagnostics? Does anyone know of a mechanic in MI that could look at the boat? I’m sure if I call off the street I’ll be in a six week waiting line. Any help anyone could provide would be much appreciated. Our season is just now getting good and my boat needs help! Thanks

I have a basic code reader that I can plug in for you I live in rochester hills. also think about a coil. PM if intereseted in scan.

You need to get a diagnosis. Hopefully you and 28ss can get together. I hope it's an easy fix. It sounds like a fuel delivery problem, but it could be caused by a sensor or module.

Fuel or the Coil sounds like

First off I'd say a coil. If not then a loose wire in the ignition system or a bad altenator. Otto

350 MPI cutting out
 

I'm adding this note so hopefully anyone who also has this issue in the future doesn't have to go through what I did. I had this same problem last summer. I chased down everything ignition and everything fuel and still had no luck. I even went so far as to check every single point of electrical contact for something loose or corroded and found nothing. It would only do it at higher RPM and very sporadically at that. Finally months into my problem I was running across the lake with every known fuel and electric test gage known to man hooked up when it started do it again. This time instead of instinctively powering back the throttle, I just let her go, cutting our and backfiring like crazy. What I noticed was a flicker in the AMP gage. I moved the Multi meter over the Alternator and low and behold it was not producing a steady current. It would spike up then drop off. When it was idling it was fine. Clearly the voltage regulator was faulty, so I replaced my alternator (VR is built in) and finally cured my problem.

I believe what was happening is the current would spike up and the ECM would power down to protect itself, as the voltage would lower back down it would come back on and repeat the cycle.

This was a horrible waste of time that I'm hoping I can spare at least one person from. If you're having this same issue with a 350 MPI cutting out, do yourself a favor and check the engine charging voltage.

WOW

Thank you so much for the follow-up

put this in the ol memory bank

3pointstar

Did you have a scan tool hooked up to the DLC while you were running around the lake ? That would have shown your voltage output thru out.

No, I'm a boat owner not a marine mechanic, I don't own a scan tool. I did throw a code reader on it which found no codes.

Also, I scanned hundreds of blogs with guys having similar issues and not one "expert" ever suggested hooking a data reader to the ECM to check operation voltage. For that matter nobody even hints at a possible connection to the alternator, at least until I reported this, then of course I get many armchair mechanics chiming in.

I just wrote this to help others, not get feedback on what I should have done.

Oh Ok just thought in your statement that was posted that you " tested with every electrical testing gage known to man ". So of course had to ask as it was a question mark.

I understand u r not a marine tech and I would have to say sometimes its best to seek one out and fix the problems that boat owners can not or the ones that have dragged on for months or years with no improvements.

I also posted to help others out on how to find your exact problem most likely showing up in a very short order. Not getting on your case nor saying anything bad here but just saying plus passing on the way to help find that issue very easily in a short timeframe. A quality scan tool can be bought for 400 to 500 bucks brand new.