Merc 5.0 alpha one cut off switch

[X8052]

hello, i really need your help. I have a mercruiser 5.0 with alpha one. The ecu seems to be for merc and bravo. The problem is that the cut off switch kills the engine when going to neutral. Is there any way to fix this without changing ecu ?

Please help me.

 

[sogood]

Are you talking about the shift interrupt switch? If, they can go out of position and can be easily adjusted. You can check its operation by operating it manually with the engine running. Operating the switch should cause the engine to "almost" cut out. Holding the switch in this position should cause the engine to cut out fully.

 

[X8052]

The switch position is correct. The problem is that the engine ecu is for merc and bravo. So with the alpha one it cuts the engine so much that it kills it.

 

[sogood]

Sorry, outside my comfort zone. I'm a carb and plugs man myself. Ecu's can help to complicate a simple idea sometimes. Hope you get it sorted.

 

[X8052]

Thanks i hope someone else have solved this

 

[QBhoy]

Hi
Usually this engine driving a bravo doesn’t need a shift interrupt switch. Only on an alpha. Just remove it. Presumably the engine came from an alpha set up and is now on a bravo ?

 

[X8052]

Hi. The set up NOW is on an Alpha. It had a bravo before therefore an ECU for it. So now with the alpha the ecu does not work correctly when the interrupting switch engages and kills the engine.

 

[spannerman]

As stated absolutely no need for cut out switch on a Bravo drive. If iit cuts the engine out its either adjusted incorrectly or the shift cable down to the drive needs changing, as they get older they get stiff, this makes the floating function on the shift quadrant operate for too long cutting the engine. It should only move momentarily as you move back to neutral, this cuts the ignition for a fraction of a second reducing the torque on the dog clutch teeth allowing them to slide out of engagement. How is it wired up, is it carb or injection. If carb it should be wired directly to the coil on a green/white wire, if its injection its wired to the ecu and doesn’t cut the ignition it retards the timing so the idle speed falls allowing it to come out of gear, the engine should keep running with the cutout held closed, whereas a carb engine will stall if held too long.

 

[X8052]

Its an alpha one drive not bravo.

 

[spannerman]

Understand you have an Alpha drive, my point is cutouts are only fitted to Alpha drive engines. A Bravo drive never has a cutout as it doesn’t have dog clutches, these hang up once engaged with the engine running making it difficult to come out of gear, hence cut out switches. Try just pressing the moving part of the quadrant once quickly so you see the microswitch operate, the engine should just stumble and pickup which is how it works normally. If it stops when you move the gear lever in or out of gear the wire is too stiff and needs changing. If it does it only on the way out of gear then check the adjustment before replacing the short wire.
Obviously the cutout is connected into your ignition switch as it is stopping the engine so it has the correct function, its just cutting out for too long which from experience tells me its adjustment or more likely the short gear wire that is your problem.

 

[airconltd]

Hi Spannerman, I Like the way you talk, I can understand clearly. I just joined !. I appreciate what I am reading here.
I have this boat (Bayliner Trophy 2329) love it. Put remanufactured engine in over a year ago and replaced most everything one at a time
I have a mercruiser 5.0l Thunderbolt, Alpha Gen 2, approx 2000, Carb fueled. Main issue at present is the engine will not briefly stall to take the pressure off the slider to allow the shift to come out of gear easily. The interupt switch will cut the engine out completely.
I did not try just bumping to see if it stumbles (looking forward to doing that) and to trace the wiring (yours colours/Coil helps a lot). I would like to share my experiences with anyone to help out, My boat is a distance away & self employed so can delays in response to replies or questions.
Appreciate any help I can get, thank you.

 

[spannerman]

I will check the wiring diagram to be sure, but from memory the cutout switch has green and white wires one goes to earth on the block and the other goes to the negative terminal on the coil, a grey wire,this will cut the ignition when the the switch operates momentariky.

 

[spannerman]

I have finally had time to study the workshop manual and on a Bravo engine there should be a white/black wire from the ignition module coming out of the harness near rhe cutout switch. On a Bravo engine this should then connect to a white/green wire which is then plugged into a black wire going back into the harness, this is the setup for a Bravo drive. When its on an Alpha drive the white/green wire should go to one of the wires on the cutout switch and the other wire should connect to the black wire, so it breaks the circuit when the switch is operated.
Hope this helps.