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Intermitant Fault with MAG 350 MPI

skyeden

New member
"Hi & Help, bought 1st boa

"Hi & Help, bought 1st boat couple of months ago, Maxum 2700SCR (2003) only 60 hrs on engine, been fun up to a few weeks ago, now 74 hrs on engine 350 Mag Mpi

Problems-
1) Notice leaving marina at idle engine missed a beat every now and again, put on plane @ 3500 revs and seemed fine, out for a hour or so returning on plane felt it miss again, came into marina and ticked over fine
2) Went out from marina and the odd miss again, just onto plane @ 4000 revs when dies, heavy smell of fuel, tried to start would occasionally fire but then splutter to a halt, towed home, back at marina fired up and ran for 15 mins at idle no problem
3) Replaced fuel/water separator filter, on draining fuel from old filter it was very dirty – no water, changed inline fuel filter as well and again really dirty from inlet side, took boat out and tested for an hour ok at all revs, thought problem fixed
3) Went out for weekend, no issues at 1000-2000 revs to destination, stayed the night, next day headed for supplies, all well for 30 mins while waiting to dock spluttered to a halt again, wouldn’t start, 1 hour later got started, running really rough, using high revs to keep running sounded like missing on a few cylinders starting and stopping then all ok, limped back to destination between 700-1000 revs never missed a beat, fired up a couple of time during the night all well, fired up in morning for 30 mins before heading home again all well, loaded up kicked in reverse and spluttered to a halt, tried over an hour to start, would occasionally start but splutter and die, towed home again
4) After being towed back tried to start at marina and wouldn’t so hey hopefully find the problem now, an engineer looked at it and she still would not start, he checked fuel pressure - ok, removed plugs pretty dirty so cleaned and re-gapped - engine now fires up but would shut down after anything from 30 seconds to 2-3 minutes, purring away then just shut off as if you switched the key off, then he phoned back to say engine now running for last 15 mins and not shutting off- arghhh
5) Decided to get Mercruiser dealer to run diagnostic test, he did with no fault codes or issues, he checked the fuel pick up wasn’t blocked says engine running away with no faults and seems to be fine, thinks sea trials required to find fault or breakdown again etc
6) Was down last night, ran engine myself for 20 mins revving etc and purring away nicely – so frustrating

Sorry for the long story but I have lost all faith in her and had the embarrassment to be towed in twice now from the same park rangers, there is clearly something not right and I guess the more information the better so any ideas guys??

Told today mercruiser dealer can't help, i need to run boat until it breaks down again before he can do anything, HELP"
 
"Did anyone remove the IAC &#4

"Did anyone remove the IAC (Idle Air Control) and clean it? Did they clean the throat and butterfly on the he throttle body. Since you found lots of dirt in the fuel filters I would want to have some strong fuel injection cleaner put in the gas tank or have the Merc. dealer connect a can of cleaner to the fuel line and run it. I would also change the spark plugs; 6 yrs., 74 hrs. and a lot of dirt says it's time."
 
I would also check your engine

I would also check your engine grounds and monitor voltage while it is running bad.
 
A bad/failing tach can kill an

A bad/failing tach can kill an engine. You can disconnect it to see if the problem stops.
 
"Hi Guy, thanks for the reply,

"Hi Guy, thanks for the reply, my engineer said the plugs were ok, as he is a marine engineer i have to take his word for it, No the IAC has not been touched, how do you do this, i'm a mechanical engineer to trade so happy tinkering arround a bit myself to save costs, can you recommend a fuel cleaner? Asits an electrnic fuel pump, pressurized etc i'm still thinking its a fuel issue with all the dirt etc we found, is there a filter on the fuel pump?"
 
"Hi Kurt S, thanks but the pro

"Hi Kurt S, thanks but the problem is it runs sweetly most of the time, i'm taking her out this week to see if she plays up again, she only ran rough the once where if i didnt keep the revs high in neutral she would have shutdown, now she is purring away at the marina?"
 
The IAC is side mounted to the

The IAC is side mounted to the throttle body (TB). Don't use carb cleaner in the throat of the TB. Use TB cleaner. Carb cleaner is OK for the IAC if you remove it.
 
"Guy,

Bit of a novice when


"Guy,

Bit of a novice when it comes to marine engines but are you talking about carbs? This is an EFI system, excuse my ignorance, thanks"
 
The engine gets its air thru t

The engine gets its air thru the TB which looks like the throat of a carb w/o a fuel bowl. It's covered by the flame arrestor.
 
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