Mercruiser 350Mag stall question

paultallett

paultallett

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Hi,

I've got a Mercruiser 350 Mag MPI thats started a new game.........

Yesterday morning when leaving from Hamble Point, I warmed her up as
usual before slipping the lines, she was out of gear at around 1200
rpm, then when I took the throttle back to the centre position the
engine stalled..... It re started straight away and I just put it down
to being one of those things even though the engine has never done
this on me before!!

The trip back to Mercury went fine, when we back in our mooring I had
a quick wizz round with the WD40 and checked plug leads and the like
was all on ok.

This morning I ran her up to temperature just to see if she would
stall again. Most of the time she was running exactly as she normally
would, I would run her around 1200 rpm out of gear and then close the
throttle down, but on 2 occasions she went to die, but picked back up
just before she quit...... She's never done this before!!

Any one got any ideas as the where I should start looking as to what
might be the culprit for this??

Regards Paul.
 
paultallett said:
Hi,

I've got a Mercruiser 350 Mag MPI thats started a new game.........

Yesterday morning when leaving from Hamble Point, I warmed her up as
usual before slipping the lines, she was out of gear at around 1200
rpm, then when I took the throttle back to the centre position the
engine stalled..... It re started straight away and I just put it down
to being one of those things even though the engine has never done
this on me before!!

The trip back to Mercury went fine, when we back in our mooring I had
a quick wizz round with the WD40 and checked plug leads and the like
was all on ok.

This morning I ran her up to temperature just to see if she would
stall again. Most of the time she was running exactly as she normally
would, I would run her around 1200 rpm out of gear and then close the
throttle down, but on 2 occasions she went to die, but picked back up
just before she quit...... She's never done this before!!

Any one got any ideas as the where I should start looking as to what
might be the culprit for this??

Regards Paul.
Click to expand...

There was a post on here recently about mercruiser engines and Googling the mercruiser and Ignition System sites pulled up lots of info. This wasn t one of the other posters problems but it was covered in some of the sites. As years are creeping on here I will have ro return to these sites to confirm the likely reasons however one reason I believe was due to faults in the protective circuitry relating to the inhibit switches on the shifters.

This was one manual that turned up.

http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF


This might not be your system but it may give clues...It might be worth rigging a small indicator light in parallel to the ignition circuit to see of the supply is being inhibited in some way. Then just a matter of finding how. Do you have a mate with a lap top and software who knows how to view the engine software as faults are held in memory and can be bought up on the screen.. Though on the older engines the fault low sea water pressure was not!! You might just have to speak to our old friend V Paul .


One source of cutting out seems to be the IAC valve sticking as discussed here.

http://www.boatered.com/forum/topic.asp?TOPIC_ID=111709

Though this also effects starting?
 
Last edited:
paultallett said:
Thanks Bilge Diver,

I've been busy searching the tinternet and most leads seem to come back to the IAC idle air control valve??...... the search continues!!
Click to expand...


There will be lots on the web as these are popular engines in the USA with lots of help forums.

The IAC valve and controls is certainly a hot favourite for your type of fault though an ignition inhibit for some reason could do like wise. I expect you have noticed that the IAC valve movement has no feed back so is not monitored:(
 
Bilgediver said:
There will be lots on the web as these are popular engines in the USA with lots of help forums.

The IAC valve and controls is certainly a hot favourite for your type of fault though an ignition inhibit for some reason could do like wise. I expect you have noticed that the IAC valve movement has no feed back so is not monitored:(
Click to expand...

Yes, I see theres no fault code that the IAC will send, I guess it will be a process of elimination, starting with the obvious...........
 
paultallett said:
Hi,

I've got a Mercruiser 350 Mag MPI thats started a new game.........

Yesterday morning when leaving from Hamble Point, I warmed her up as
usual before slipping the lines, she was out of gear at around 1200
rpm, then when I took the throttle back to the centre position the
engine stalled..... It re started straight away and I just put it down
to being one of those things even though the engine has never done
this on me before!!

The trip back to Mercury went fine, when we back in our mooring I had
a quick wizz round with the WD40 and checked plug leads and the like
was all on ok.

This morning I ran her up to temperature just to see if she would
stall again. Most of the time she was running exactly as she normally
would, I would run her around 1200 rpm out of gear and then close the
throttle down, but on 2 occasions she went to die, but picked back up
just before she quit...... She's never done this before!!

Any one got any ideas as the where I should start looking as to what
might be the culprit for this??

Regards Paul.
Click to expand...

I have twin Merc 4.3EFi's on my boat and I'm familiar with this scenario (though I can't advise how to correct it because I'm not a mechanic!!!) and I reckon the problem almost certainly lies with the gear linkage adjustment and the micro-switch that is meant to cut out the engine momentarily. It just needs re-adjusting by someone who knows what they are doing, and not someone who thinks they know what they are doing - otherwise the problem will probably get worse not better.
 
Thepipdoc said:
I have twin Merc 4.3EFi's on my boat and I'm familiar with this scenario (though I can't advise how to correct it because I'm not a mechanic!!!) and I reckon the problem almost certainly lies with the gear linkage adjustment and the micro-switch that is meant to cut out the engine momentarily. It just needs re-adjusting by someone who knows what they are doing, and not someone who thinks they know what they are doing - otherwise the problem will probably get worse not better.
Click to expand...

To be honest that's exactly what I first thought.... But at no point did I put the engine in to gear when the stalling has occured.... But that's not to say that some how the switch isn't coming in to play when closing the throttle out of gear.... Even though the switch should only work when going in and out of gear.
 
paultallett said:
To be honest that's exactly what I first thought.... But at no point did I put the engine in to gear when the stalling has occured.... But that's not to say that some how the switch isn't coming in to play when closing the throttle out of gear.... Even though the switch should only work when going in and out of gear.
Click to expand...
Two points:-

1) Depending on what outdrive you have got on the boat, you may or may not have a shift interupt switch. Check first whether or not you have one before trying to see if it is working properly. :)

2) The switch should only operate (when working correctly) when taking the boat out of gear.

These switches do fail in odd ways, so its worth replacing if you have any doubt.
 
lovezoo said:
Two points:-

1) Depending on what outdrive you have got on the boat, you may or may not have a shift interupt switch. Check first whether or not you have one before trying to see if it is working properly. :)

2) The switch should only operate (when working correctly) when taking the boat out of gear.

These switches do fail in odd ways, so its worth replacing if you have any doubt.
Click to expand...

I believe this circuit and fault is mentioned in the Ignition Manual for which I gave a link earlier.
 
lovezoo said:
At the moment we don't even know if the OP has a shift interrupt switch on his engine, but if he does it would be the first place I would look as the symptoms are exactly those of a faulty switch.
Click to expand...

It's a Bravo 3 Drive, so yes it does have the shift interupter switch. I did lift the hatch and watched that the shift system wasn't moving when I applied and closed the throttle...... I couldn't see any movement, so as you say it would give my symptoms but with me not being in gear when the engine tries to stall, and with her running fine at all other times, I'm guess it's least likely to be this........ but I can't be sure until it's been checked and ruled out....
 
Was the boat actually in the water when you looked? The interruptor switch will only operate when there is a load on the prop.

I thought you said it stalled when you shifted into neutral? That is exactly when the switch operates, so if it is faulty or badly adjusted it could be the cause.
 
lovezoo said:
Was the boat actually in the water when you looked? The interruptor switch will only operate when there is a load on the prop.

I thought you said it stalled when you shifted into neutral? That is exactly when the switch operates, so if it is faulty or badly adjusted it could be the cause.
Click to expand...

Yes boat is in the water........ I might not have been clear in my original post :) but I was warming her up OUT OF GEAR and when I brought the throttle back to the neutral position (ie so I could then engage forward) was when she stalled...........

And on the other occassions the engine was OUT OF GEAR.......when I closed the throttle was when she went to die, the engine hasn't done it YET when I've been in gear..... but it's probably only a matter of time!!
 
Bravo drives don’t have a shift interupter switch, only Alpha drives. What you were looking at is the shift quadrant which won’t move if you select throttle only, it sounds like your IAC valve is playing up, you can try taking it off and cleaning it with carb cleaner otherwise it will need a new one.
 
Matt Taylor said:
I know this is an old post but I would love to know if you fixed this problem as mine is the same and its driving me mad
Click to expand...
Hi. I have a v8 mpi. There are a few common things to be aware of. The distributor cap is the most famous or them all. Causes all sorts of issues after storage especially. They can gather dampness too easily. If it’s an alpha, coming out of gear and stalling can mean a shift interrupt switch for sure. The IAC is a culprit too. Doesn’t always alarm but can give 2 beeps on the dash if it’s totally failed.
 
Hi thanks for the help. I have already changed iac valve and muffler.

Just to be clear, the only problem is when the motor goes back into idol, it starts in idol with no problem but it always drops the revs to below 300rpm when returning to itdol for 1 second, then normally recovers back to 570rpm but somtimes stalls causing docking problems. It will start again in idol with no problem and run with no misfires. this also hapens out of gear (Bravo 3)

Im not sure when this started but I have changed the elbows and had exhaust bellow leaking taking on some water. At this point I checked the distributor for damp I have also changed the heat exchanger. Is it possible to have pulled a wire out or a vacume hose? I have checked but cannot see anything.
 
I’d be suspecting fuel quality after reading more of what you’ve said perhaps. At the risk of harping on about it…and just from experience…just never frost those diz caps. They are just bad full stop. I’ve went through 5 of them in 7 years or so. One even failed from new. If that’s not part of the issue now…it will be part of it all of an issue later. Terrible things. Will definitely let you down at some time for sure. Often costing a fortune in diagnosis and parts change out, for those who aren’t aware of their many issues. They can look perfect…but just aren’t. You may also have an issue where you’re drawing air perhaps. This could cause such a thing. Anyway. Best of luck and hope you get it sorted soon.
 
If any one else gets this problem it was an easy fix. The throttle body was not sealing properly when put back into idol and the IAC was taking a second or two to compensate. Cleaned the throttle body and all was good.
 
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