350 mag won't stay running

halifax212

Had a great day on the water today. Boat ran fine. Loaded it on the trail and brought it home to flush. Engine started fine , then after a few minutes it seemed to idle rough and early seemed to stay running, then a stall.  First time in 9 years I had an issue.  Went to restart. Turned the key ,heard the pump run for 5 seconds then start. Some fire but dies out. Looking for the obvious before I take it somewhere for service. Are there any driveway pointers I can try?  First time the ol girl has let me down. 2004 350 mag MPI. 

Liberty44140

When did you last do fuel filters, spark plugs, cap & rotor? 

GMSLITHO

yep start with fuel /water seperator 

halifax212

@Liberty44140 I think 2015 , wires rotor cap , plugs maybe 2014.  Just seems odd that there was absolutely no indication and any problems finishing up the day to the flush. Will head out in a few minutes to look at the points on the cap. 

halifax212

fuel filter new this season with only a few hours on it.  I guess I will have to have a look there too.  

halifax212

@GMSLITHO. heading out now to check that as well.  Thanks

Brian

halifax212

will start with filter , cap and rotor.  Hoping wires are ok. 

aero3113

Yes, definitely time to replace the cap and rotor!

liuxue2010

Try to give a little bit throttle and if it's working, meaning IAC controll bad so just replaced. 

rinker270nb

It starts and then dies? Or, it can't turn over when starting?  Is engine cold or hot...IAC is usually when you put into great at transition.

https://rinkerboats.vanillacommunities.com/discussion/comment/116645#Comment_116645

halifax212

@Alswagg , funny you asked if the bow was down. I did appear to be so I backed it a bit further up the driveway until level.  Same result.  Replaced the cap and rotor today, no change. Replaced the plugs from 2013 today as well.  The boat shop I purchased the cap from said there was wear but did not think enough to cause the problem.  He sold me replacement "mufflers" for the IAC. Couldn't find the old one to replace....turns out there wasn't one where there should have been one.  The spark plugs all looked good, mostly tanned and still gapped close to 60 point. I ordered an IAC today that will be here tomorrow.  @rinker270nb , it does fire very weak, then dies.  

212rowboat

It sounds to me like your coil. 

Willhound

I was going to suggest the Orange wire that runs from starter motor to coil.

Handymans342

Yes, 12 volt problem. Sorry to hear my friend

halifax212

Hmmm. I am hoping that if the IAC does not fix it I can return it and then focus on the coil / wire.  The season is so short here  that this is painful(especially since I am on vacation this week) I will look into the orange wire as well in the morning. I'm grateful though, that it did not fail with the Admiral on board at the mouth of the Bay looking at open ocean. No Sea Tow bill and the Admiral may still want to go out on the water with me.  I have a feeling it will be road trips for the next week.  

Liberty44140

yea leave that IAC in regardless, now you know its done

rasbury

What's the orange wire?

Willhound

Runs from the positive lug on the starter to the coil. Provides a nice clean 12V boost to the coil to keep ignition strong. When I first got my 270 it had a periodic miss that we attributed to old fuel. On plane it would suddenly cut out for a split second just like somebody quickly turned the key off and on. Changed plugs, rotor and cap. Changed water separator about 6 times. Started running worse, got hard to start and finally wouldn't start at all. By that point a loose wire had become a disconnected wire. Mechanic figured it out by running a jumper from battery to coil and it fired it right up. New wire and connections and it's run like a champ ever since.

212rowboat

coils usually last a long long time...

when they start to fail it happens over many cycles- the isolation material literally splits like a log through its axis... when heat allows the casing expansion enough, the isolation material comes apart and allows that beautiful spark exit (or enough ground found to weaken it's voltage, rendering it useless) but when it cools? varoom- it works again.  until it expands (doesn't need much room to let the juice out) under heat it will work just fine.  as soon as it expands it stops.. 

that^ makes it a trick to diagnose.  

at some point, the coil finds enough ground to stop working altogether, not even allowing the engine to run (fire? yes... run? no)... and driving folks nuts trying to t/s it.  unless they've seen it before... then, it's pretty obvious. 

fat yellow wire, or coil.  yellow wire just as if not more likely than the coil. 

halifax212

I ended up taking the boat to the shop for them to figure it out.  I swapped out the IAC but did nothing. Realizing all I can do is throw parts at it , I decided to give it to the boat shop.  @212rowboat  sure would like to have tried the jump as described.  I had already made the call to purchase a new coil as my next step. The supplier said I should really be sure that is what I needed because after tax it is a $600 part that cannot be returned. That is when I call the boat shop.  Should know by the end of the week. I am prepared to B.O.A.T.  My son is leaning toward fuel pump / low pressure.  

212rowboat

$600? Wow.  

69fastback

The coil is $600?

rasbury

So, this wire is still a mystery to me as I do not have one....Is this on older type motors? Mine is an 06 MPI electronic ignition and to be honest never looked to see if I had a coil or where it is located....not a mechanic for sure just a good DYI guy...

raybo3

If this is the same part its only $298 on amazon.com. 
https://www.amazon.com/Mercruiser-2001-2004-392-863704-392-863704T-8M0054588/dp/B06XWDQRK7/ref=sr_1_3?keywords=2004+350+mag+MPI+coil&qid=1562856899&s=gateway&sr=8-3

212rowboat

for a part as expensive as that, i'd do some more extensive troubleshooting first... by extensive, i mean i'd go to the parts store and grab a $50 coil with a return policy- and WHILE ON THE HARD and with well ventilated engine compartment, give it a go.  if she runs? get a refund and order the marine rated/specific coil... 

but more importantly that that^, i hope the quoted price includes the lube and the parental prevention/protection from creepy crawly's.  

https://www.wholesalemarine.com/mercruiser-ignition-coils/

Willhound

rasbury said:

So, this wire is still a mystery to me as I do not have one....Is this on older type motors? Mine is an 06 MPI electronic ignition and to be honest never looked to see if I had a coil or where it is located....not a mechanic for sure just a good DYI guy...

Likely not needed on electronic MPI. Mine is a 2000 with 5.7 EFI. Basically a mid 80's Chevy TBI.

halifax212

The part is $520 plus tax...our rate in NS is 15% . Don't forget our dollar is crappy right now so 300 USD  is about $420 CD .  Then there are duties and shipping.  Hoping a bad ground......stay tuned! 

Brian

halifax212

PS. My coil is the coil/module combo that Raybo forwarded to me above

halifax212

Well I got my boat back today with some good news. There was a lot of air which they had to bleed off along with possible flooding from all the restart attempts. It fired up for them and held idle. They feel it was the IAC valve I replaced. Tested it in the Bay today and ran fine(new plugs rotor and cap as well).   I placed the IAC sponge in the throttle body but I find that the idle is too high now (1000 rpm) Will the computer "learn" after a while and settle back to around 650 rpm? Shifting sounded hard today because of it.  If I remove the sponge filter will that help bring it down?  The only other thing is the throttle handle does not seat into a locked neutral position anymore. I no longer have to press the button to shift out of neutral for forward or reverse. I feel I may have been stalling the engine a few times today making sure it was fully in neutral by tripping the shift interrupter switch .  Best thing was my bill at $55 today!

Handymans342

Keep us posted

rasbury

Sounds to me a of stuff that has nothing to do with each other but if the throttle is not working right then it sure can be messing with the idle I would think?