115 MERC fourstroke intermittent issues SOLVED

 Just following up on a previous post of mine trying to get to the bottom of this intermittent problem I had with my 2016 115 mercury.

This was my previous post http://fishwrecked.com/forum/115-merc-fourstroke-issues

So just a quick once over. I was experiencing a random period where the motor would run rough at lower revs and every now and then it did it at higher revs while driving in gear. After replacing every fuel line, completelty emptying and cleaning the tank, changing the tank pick ups, breathers, filters, spark plugs, loose electrical connections, pulling the control box apart etc I couldn't solve the problem. It didn't happen every time so you can imagine it was nearly impossible to take to a mechanic and say "fix it". The computer had never logged a fault or alarm so I was beginning to think I wasn't gonna get to the bottom of it.

After hours and hours searching through forums online I read an interesting post a bloke made experiencing a similar problem and his fix was a shift position sensor. I originally thought this is the "neutral position switch" that is in the control box that prevents you from starting the motor while you are in gear but its a different sensor. This sensor is actually in under the motor cover where the shift selection is. Tells the motors computer exactly when it's in forward reverse and neutral. Not sure if anyone else has done this but if you rev your motor up in neutral it limits the revs to about 2500 revs (or around about) and the motor shakes around like crazy and it doesn't sound nice. Obviously the computer doesnt want you to be able to rev the shit out of your motor while in neutral.

So what was happening was this switch was playing up. As I'm driving along at say 3000 rpm the switch for a spilt second tells the motor I'm in neutral and the computer limits the revs causing the motor to run rough. This malfunction with the switch was so fast it doesn't log a fault and you can't see it when plugged into the computer but would tell the motor to limit the revs.

My mechanic got on the phone to some other Merc mechanics over east and apparently there's been a few other cases like this around Australia. Merc said they will cover it under warranty since we've tried pretty much everything else. Changed the switch for a new one and I've been out about 7 times since and she hasn't missed a beat. 

Hope this helps anyone experiencing similar problems. The problem was eating away at me for a good 6 months. Pays to keep digging there's plenty of people on the internet with problems you can learn from.  Another fix i read with some of these strange problems is a faulty crank shaft position sensor. Can also cause issues. Before you go pulling apart your fuel pump or replacing the computer try replace these sensors (relatively cheap) when fault finding may end up saving you some money.




Posts: 52

Date Joined: 09/01/12

 That's very interesting, I

Fri, 2020-06-19 17:54

 That's very interesting, I have a Merc four stroke that had an intermittent pause at high rpm, but no codes thrown. The mercury dealer couldn't replicate it and ended up replacing the throttle position sensor as you did. Hasn't happened since. 

dmck's picture

Posts: 195

Date Joined: 07/03/19


Fri, 2020-06-19 18:35

 on your perserverance.  Problems like that are diabolical to resolve.


You have done well and can be proud of your effort.

Posts: 5981

Date Joined: 17/06/10

Well done

Fri, 2020-06-19 18:59

Persistence pays off 

Posts: 171

Date Joined: 08/09/11

 Similar issues with my 115

Tue, 2020-06-23 13:48

 Similar issues with my 115 suzuki. Replaced the shift position sensor at the front of the motor and problem hasn't reoccured. 

Adam Gallash's picture

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Date Joined: 29/11/05

Interesting read

Wed, 2020-06-24 20:32

 Interesting read. Cheers for the post Mitch.


Site Admin - Just ask if you need assistance

Posts: 579

Date Joined: 28/11/16

Awesome news. Thanks for

Fri, 2020-06-26 16:30

Awesome news. Thanks for sharing  

scuttlebutt's picture

Posts: 431

Date Joined: 24/03/06

 Same sensor in my 2007 merc

Wed, 2020-07-01 19:22

 Same sensor in my 2007 merc optimax 200 shit itself with only 50hrs on it.  Went into safe mode and ruined a trip.  I got the mechanic to remove it completely.  I don't need a sensor to stop me from over-revving my motor in neutral...

little johnny's picture

Posts: 4363

Date Joined: 04/12/11

So you can

Thu, 2020-07-02 09:20

Get them removed. My Andy had same issue with his optimax. Caused heaps of pain for a low priced part .

scuttlebutt's picture

Posts: 431

Date Joined: 24/03/06

 Yeah dunno if you have to

Thu, 2020-07-02 18:41

 Yeah dunno if you have to use a jumper wire across the terminals but mine's been running fine without it for 8 years now.