Mercruiser MPI shift interrupt

[QBhoy]

Hi

after a favour guys...
would somome possibly be able to send me a video of their merc 350/5.0 MPI (or identical set up) shift interrupt micro switch being activated as it’s shifted into gear please ?
Mine was causing problems in the season and activating when at WOT.
Its now apparent that it isn’t actuating when going into gear. Only when coming out of gear.
It was dark when I was trying to see it last time, but would like to go and have another look, armed with what it should be like.
Its an Alpha.
Thanks.

 

[alldodge]

Only when coming out of gear.

I should only work coming out of gear when in the water. It should not work any other time, and should not work out of the water.

Check your adjustment and assure its lubed

 

[QBhoy]

Thanks AD. You think it shouldn’t drop the rpm when going into gear ? If so that would make sense of it maybe. I thought it did it in and out of gear ? It does it coming out of gear for sure.

 

[Bt Doctur]

only coming out of gear, in the water , no other time.

 

[achris]

And only if there is load on the prop. Meaning if you are still coasting forward and the water flow is 'unloading' the prop, it will not interrupt...

You may want to check the 'in gear' switch. If that's out of adjustment, or failing, then the ECU will detect 'out of gear', and it limits the revs to 3000...

The dropping of revs as you go into gear is also normal. You're loading the engine... Also, do a data dump of the ECU, it will have 'idle rpm' for neutral and 'Idle rpm' for when it's in gear. They are different. As you drop it into gear the ECU adjusts the fuel and air flows to achieve the right idle speed, and that as you load the engine, so yes, your revs will drop momentarily..

Chris........

 

[QBhoy]

Thanks guys. It just seems harsh going into gear. I’m amazed it doesn’t drop the revs doing this. That’s what I always presumed it would or should do.

 

[QBhoy]

Ok. I’m perhaps thinking now that my mooring in a fast flowing river may have an effect on things. The prop turns in the current constantly

 

[alldodge]

Ok. I’m perhaps thinking now that my mooring in a fast flowing river may have an effect on things. The prop turns in the current constantly

Yep, I can see that being a factor

See if you can find one of those leprechauns and get enough to change over to a bravo drive

 

[QBhoy]

Ach...T’be sure...that would only slow me down.
Just on that note, whilst a friend was going to slip his boat for winter, the belt snapped on his 350 bravo. Overheated real quick. Lucky he caught it. No such danger on an alpha, haha.

 

[Lou C]

The interrupt should be reacting to pressure on the lower shift cable; that should only be present when shifting out of gear. If it is engaging going into gear I’d suspect a sticky shift cable or other parts of the linkage.

 

[QBhoy]

Thanks. It’s not engaging going into gear...but it occasionally is at wot.

 

[Lou C]

Merc must have a way to prevent that, on the OMC Cobra it has an overstroke switch that prevents the ESA from engaging once the drive is shifted into gear...

 

[alldodge]

occasionally is at wot.

As before adjustment or need some lube

Bring back up only to ask another question; you sure its the interrupter that is the cause, or maybe its an ignition issue?

 

[QBhoy]

Ad. It shows a fault on the error list when it happens. If I mess with it and spray lube it fixes for a while, but eventually just touches it again. I need to adjust it slightly on its mount I think.

 

[alldodge]

If I mess with it and spray lube it fixes for a while

Sounds like something is dragging. When you give it more throttle something is causing it to move the plate. Have someone move throttle to WOT while watching the plate

 

[QBhoy]

Thanks All dodge. It’s really hard to replicate it.
Dont think it will happen when wot in neutral, nor do I really want to try that...and almost impossible or just daft to do it at wot in the move trimmed up. Only happens at the absolute limit trimmed up mid to late 60’s. Just taking a wee nudge every now and then. Defo better after I messed with it and lubed it. Haven’t tried any more than that. I’ll take it all to bits during winter. Thanks for the drawing.

 

[alldodge]

Wasn't want you to try it with the motor running, just sitting and motor off.
It being trimmed way up, do you think you might be hitting th rev limiter?

 

[QBhoy]

Wasn't want you to try it with the motor running, just sitting and motor off.
It being trimmed way up, do you think you might be hitting th rev limiter?

Ah. I’ve had a look at it stationary and it just seems normal to me. Just couldn’t figure why it wasn’t engaging it going into gear. Now I know.
I only know it’s doing it at wot after looking it up and the fault that shows instantly afterwards, see picture from vessel view.
It’s a bit of an event when it happens. Looking at plugs it’s clear that 4 of them are more blackened from it happening. When the shift interrupt activates and killing 4 cylinders. Also read on here about others having the same problem.

 

[alldodge]

Looking at plugs it’s clear that 4 of them are more blackened from it happening.

This would have me scratching my head real hard trying to figure out how that would happen. If there all running the same mix, an instant miss IMO would not cause one to get more black then the other. For something like that I would look at those injectors or the wiring feeding them (+/-)

Don't remember if we know if you have individual or batch firing

 

[QBhoy]

Ad. Perhaps only because it did it so often. At one point it was doing it every time I opened it up. Then I was failtfinding and doing it some more. This was over a period of around a month. In this time it would have happened around 50+ times or more.
Injectors could be a contributing issue I suppose. The boat has now done over 600 hours and may be due a change out or check at least.