Intermitant Fault with mag 350 MPI

[gentlemanglobetrotter]

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

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??

[seapuppy]

well..more data would help....what sized engine and is it carbed or mpi??....might be either a filthy carb from the statement on filters....or an intermittent bad coil.........but that's only a guess since I'm not there to hear it miss or die..........


welcome to the zoo by the way..

SP :hello:

[gentlemanglobetrotter]

Originally Posted by seapuppy

well..more data would help....what sized engine and is it carbed or mpi??....might be either a filthy carb from the statement on filters....or an intermittent bad coil.........but that's only a guess since I'm not there to hear it miss or die..........


welcome to the zoo by the way..

SP :hello:

Hi i was thinking there was a clue in the subject header "Re: Intermitant Fault with mag 350 MPI" lol

[seapuppy]

DOH!!...i should try and get some caffiene in the morning before I answer these things....dang......



SP

[seapuppy]

man..that just sounds strange.....so...places to check in my mind..since no codes showed up.....check the huge plug that connects the engine to the harness....check all connections to the module and computer....make sure they are tight...check the connections to the interrupter switch....then check the connector to the throttle assembly....then there's the switches that your lanyard connects too to shut the engine off..this is an electrical problem and about the only way to find it is to trace everything down.....sorry can't point a finger at it..but these are a real pain..
someone else hopefully will toss a few ideas in here...


SP :hello:

[gentlemanglobetrotter]

Originally Posted by seapuppy

man..that just sounds strange.....so...places to check in my mind..since no codes showed up.....check the huge plug that connects the engine to the harness....check all connections to the module and computer....make sure they are tight...check the connections to the interrupter switch....then check the connector to the throttle assembly....then there's the switches that your lanyard connects too to shut the engine off..this is an electrical problem and about the only way to find it is to trace everything down.....sorry can't point a finger at it..but these are a real pain..
someone else hopefully will toss a few ideas in here...


SP :hello:

Hi SP, yes going to have to go over them all with a fine tooth comb, i had a guy on the boat doing a tonage meaurement to do with registering with the shipping act etc, anyway i never met him, his wife phoned asking for access to the boat, she mentioned without keys as long as he could get access to the engine which of course he could, funny problems started after his visit, thinking did he accidently knock a cable or something while he was down there in the engine bay - possible i guess, will keep you posted

[gentlemanglobetrotter]

Update - Had the boat out all weekend on the plane giving it plenty, would appear the gremlins have disappeared for now anyway

[seapuppy]

well..that's great news....any idea what changed??...


SP irate:

[Cobalt293]

Hi

I have had a similar problem with one of mine 350 MAG MPIs - It was the fuel pressure regulator - wich regulates the fuel pressure and also increases it when vaccum in carb. increases.

Sometimes the engine ran great... but sometimes it smelled a lot of fuel and black smoke, when idleing for a while it died... and was very hard to start. I had to clean the spark plugs... and held the cable from the ignition coil ~aprox. 1 cm above distributor(use gloves and keep your hand high up on the cable fram the dist.

You should also check the vaccum cable when engine running for leaking fuel...

I changed the pressure regulator.. and it ran great - you should also be able to identify this fault by using a fuel pressure meter.. on the rail.

As the fuel pressure regulator is fully passive it won´t show up any fault codes.

Good luck!

[gentlemanglobetrotter]

Originally Posted by seapuppy

well..that's great news....any idea what changed??...


SP irate:

Still convinced it was dirt in the fuel lines, think maybe its finally been fired through, in reality the only two things that were done were inline fuel filter & water seperator/fuel filter were replaced and the plugs were removed, cleaned and re-gapped

[gentlemanglobetrotter]

Originally Posted by Cobalt293

Hi

I have had a similar problem with one of mine 350 MAG MPIs - It was the fuel pressure regulator - wich regulates the fuel pressure and also increases it when vaccum in carb. increases.

Sometimes the engine ran great... but sometimes it smelled a lot of fuel and black smoke, when idleing for a while it died... and was very hard to start. I had to clean the spark plugs... and held the cable from the ignition coil ~aprox. 1 cm above distributor(use gloves and keep your hand high up on the cable fram the dist.

You should also check the vaccum cable when engine running for leaking fuel...

I changed the pressure regulator.. and it ran great - you should also be able to identify this fault by using a fuel pressure meter.. on the rail.

As the fuel pressure regulator is fully passive it won´t show up any fault codes.

Good luck!

Hi,

I had a fuel pressure gauge on to check pressure all seemed ok, and def no fuel leaks in or arround the engine, but i'll keep it in mind if the gremlins reappear, cheers

[rteebo]

I've been having the same problem all summer. I have the same motor in my boat. I had a mechanic tell me it was fouling cylinders and arcing off of the block. I did some routine maintenance on the ignition system as it is ten years old now, replaced plugs, wires, cap, rotor, ignition sensor, but it didn't work. I am now looking at the fuel system. I checked the fuel pressure last night and it read 23psi, is this proper?

[Dodgezilla04]

mine would do it too. 5-10 minutes and then she'd begin sputtering and crap out on me. 1/2 later, she'd run again.
found it late at night when running it in the driveway... when it started to sputter, i could see little blue lightning bolts under the engine cover...
the coil tower was cracked allowing it to arc to the secondary wire..... killing the ignition. when the coil cooled, the crack shrunk and she'd be fine until hot again..

$54 coil and all is well.

[gentlemanglobetrotter]

Hi all, well nearly a year down the line and still have this intermittent problem just back of the water today where I went out and ran at 1500rpm for approx 1 hour then as I approached a jetty for docking down to 700rpm she stalled.

Fired up 1st time and headed away from jetty, 5 minutes later started to splutter I was at 2000rpm where she would cut out down to 1200rpm then re spark back to 2000rpm did this a few times then finally chucked it

Got her started again and decided to gun it home got onto plane then she spluttered a little so I came of plane, waited 1 min then put back on plane and headed home without another blip even had her at 5500 WOT

Some history since my last post I have had another engineer look at her with all the up to date diagnostic gear where he connected up the laptop but still showing no fault codes, when he was looking at her she would not fire up so he traced this to the distributor which we removed and cleaned although I suspect when he was not getting a spark at the plugs this was because it was not sparking from the coil but as its intermittent when he then tested the coil it seemed ok, I mention this as the weeks have passed I have broken down a few times and when I try to start her and she just cranks over and does not fire I have proved 3-4 times that I do not have a spark coming from the coil when cranking over

So having seen no spark from the coil I decided either the coil or module was away so in rip off Britain I paid £220 for a new coil and module thinking at last I have fixed this and it was probably a dodgy ignition module but you cant buy them separately over here as I said rip off Britain

Unfortunately when I went down under the hood and removed the ht lead from the coil on the distributor connection to check for a spark today there was hence she fired up so next up is the ecu/ecm???

My local mercruiser dealer thankfully has a spare 350mag now with a cracked block so I have access to all the electrical bits and pieces.

As I have seen the no spark from the coil side what else can cause this I mean what all is in the electrical circuit to check or replace that can intermittently stop the coil from sparking, arghhhhhhh

[seapuppy]

bout the only things you have are the coil...ignition module...ignition switch..a breaker...and a key.........so..if your not getting spark at certain times...one of those items may be intermitten...now one other thing to check..you should see a huge connector on top of the engine...pull that apart and clean the contacts...re-grease it with dielectric grease and re-connect.....

keep us informed...and thanks for posting back on this one..

SP

[ss3964spd]

Since no one can find the exact cause you are reduced to throwing parts at it. Can't quite tell if you actually replaced the ignition control module and coil or not. If not, do so. I've seen the ignition modules run just fine when cool, but act up when hot.

Also, if you've not done so, get a copy of the wiring schematic, so you can trace the entire ignition circuit. Definately do what Dodge mentioned above - start the engine, get it warmed, and open the engine cover - at night, the darker the better.

Finally, check your ground connections, especially the one that is probably bolted to the rear of the block.

Dan

[gentlemanglobetrotter]

Originally Posted by ss3964spd

Since no one can find the exact cause you are reduced to throwing parts at it. Can't quite tell if you actually replaced the ignition control module and coil or not. If not, do so. I've seen the ignition modules run just fine when cool, but act up when hot.

Also, if you've not done so, get a copy of the wiring schematic, so you can trace the entire ignition circuit. Definately do what Dodge mentioned above - start the engine, get it warmed, and open the engine cover - at night, the darker the better.

Finally, check your ground connections, especially the one that is probably bolted to the rear of the block.

Dan

Hi Dan

Yes i did replace ignition coil & module

Any idea where to get a copy of the wiring schematic from as i want to check every connection here

Will go down at night and have a look

Cheers

[captainron]

So here it goes..I had the same problem with one of my 350 mag mpi motors.I was at the point of ripping off the fuel injection
and going with carbs.I had the advantage of swapping parts from the good running engine.I finally swaped ECM´s and found out that the ECM was acting up when it warmed up. New ones cost to much so I installed a bilge exhaust fan and ducked the air over the ecm.Problem solved.If I forget to turn on the fan she will act up.I know I will need to replace the ecm soon.But, untill then this works.I hope this helps.

[gentlemanglobetrotter]

Originally Posted by captainron

So here it goes..I had the same problem with one of my 350 mag mpi motors.I was at the point of ripping off the fuel injection
and going with carbs.I had the advantage of swapping parts from the good running engine.I finally swaped ECM´s and found out that the ECM was acting up when it warmed up. New ones cost to much so I installed a bilge exhaust fan and ducked the air over the ecm.Problem solved.If I forget to turn on the fan she will act up.I know I will need to replace the ecm soon.But, untill then this works.I hope this helps.

Interesting Captainron as that is next on my list, i am lucky that my Merc dealer has a spare Mag 350 with a cracked block (insurance replaced) so i now have access to all the bits i need to try, i have the ecm, the HT lead for the coil also another switch for being in gear or somethingto try

As the spark is intermittent and as far as i'm aware the ecm takes the inputs from sensors ie crank sensor etc and then must output to at least the coil or ignition module to tell it when to spark then this is my next diagnosis that the ecm is breaking down and i so so so hope your right mate although if it proves to be i may try your fan idea as i see they are approx $1100 to $1400 for new, try $2500 in rip of Britain

[gentlemanglobetrotter]

Changed ECM along with start neutral safety switch & HT lead from coil, problem still exists so hoping to get crankshaft sensor and power relay to change over

I think after that its then down to a dodgy connection