2016 Mercruiser 4.5l Shift Interrupt switch

[Phil Chieco]

Hello, I recently purchased a 2016 Hurricane deck boat with the new 4.5L Mercruiser engine. I have had several occasions where the engine has stalled when coming into dock.. This is certainly annoying and has been sometimes dangerous if not for my passengers stopping the boat from hitting. It seems to be an intermittent problem and happens when either slowing down from forward to reverse or just slowing the boat down to almost neutral. It's also happened from going from reverse to forward. The boat would completely stall and I would get a series of beeps and it would take about 10 - 30 seconds to reset itself so I could restart. My question is, could this be related to the Shift Interrupt switch and is this something I can adjust? Any assistance would be appreciated on how to adjust this properly.

 

[BillK]

Is this a carbureted engine or EFI? If EFI I would also look at the IAC. But it sounds more to be the shift interrupt switch or the shift cable itself. In case you don't know how this works, the shift interrupt switch is activated by the movement of the lower shift cable, it really is just a ground switch for the ignition that causes the engine to stumble just for a second so the F or R gear can be released - this "stumble" happens when shifting OUT of F or R, not when shfiting from N > F or R. The switch itself can fail, but more common the shift cable get's out of adjustment from wear and is simply activating the switch at the wrong time and causing the engine to completely stall. Google Alpha I shift cable adjustment -- there is a specific process to adjust the cable properly.

 

[Phil Chieco]

Is this a carbureted engine or EFI? If EFI I would also look at the IAC. But it sounds more to be the shift interrupt switch or the shift cable itself. In case you don't know how this works, the shift interrupt switch is activated by the movement of the lower shift cable, it really is just a ground switch for the ignition that causes the engine to stumble just for a second so the F or R gear can be released - this "stumble" happens when shifting OUT of F or R, not when shfiting from N > F or R. The switch itself can fail, but more common the shift cable get's out of adjustment from wear and is simply activating the switch at the wrong time and causing the engine to completely stall. Google Alpha I shift cable adjustment -- there is a specific process to adjust the cable properly.

Hello, This is the new 4.5l mercruiser engine, 250hp manufactured by Mercury, it's a 2016. Yes it is EFI. Can you provide the process to adjust the cable as I will try that first. Hopefully it would apply to this new model. Do you have any instructions on how to test the IAC on this new model as I would like to rule that out as well. I have not been able to find the repair manual specific to this motor yet. Thank you

 

[ddurand]

The shift interrupt is only on a Mercruiser with Alpha drive. Is that the outdrive you have? You should be able to find directions on how to adjust it by doing a Google search. It's specific to the Alpha drive not to the engine you have.

 

[Phil Chieco]

The shift interrupt is only on a Mercruiser with Alpha drive. Is that the outdrive you have? You should be able to find directions on how to adjust it by doing a Google search. It's specific to the Alpha drive not to the engine you have.

Got it. I have an Alpha Drive. Do you have any instructions on how to test the IAC on this new model as I would like to rule that out as well.

Thank you

 

[ddurand]

Mercruiser on the Alpha drive brings the shift cable from the control at the helm to the engine where it connects to the lower shift cable which goes to the outdrive. Should be easy to find. There should be a microswitch of some kind there that interrupts the engine ignition when coming OUT of gear. You should be able to press the button on the microswitch with your finger or a screwdriver and stop the engine. It's not very complicated.

 

[BillK]

Shift cable adjustment:

Google Mercruiser IAC valve and there is tons of info. I personally have never had to deal with one (my boat has a carburetor), But in general it's an IAC problem if:

• Engine stalls, runs rough or stalls at idle.
• Engine will not start unless you advance throttle.
• Engine will start and run fine when cold, but as it warms up starts to idle rough and stall.

The IAC is not expensive - it's a part that you can use the automotive equivalent. I hear many people keep a spare, it's a common problem on marine engines.
I would check the shift cable adjustment first, that doesn't cost anything but your time.