Merc 80hp 4stroke restarting itself???

[MarkCinAus]

Hi. I have a 80hp Merc 4 stroke that has run flawlessly for the past seven years. Was a mile offshore yesterday with the engine in idle when it suddenly restarted itself. I could clearly hear the starter motor engage and then it just kept idileing like normal. Fast run back into dock and no probs with engine. At dock reverse gear was crunching and difficult to fully engage - not sure if that’s related. Engine restarted itself again at dock and a third time when I was flushing engine.

Any ideas? I’m totally stumped as seems highly unusual. Can’t get into dealer for three weeks and anxious to get back on the water!!

Thanks folks.

Mark

 

[Texasmark]

Strange problem. First off the solenoid has to energize before any power is applied to the starter motor. On solenoids ready for replacement, due to high usage, the contacts pit and the surface area is reduced so when the starting current runs through there they actually weld together and releasing the key and de-energizing the coil that activates the solenoid, the current remains because the contacts can't disengage. So you turn the key to start, the solenoid closes, the starter spins and starts the engine....you release the key and it springs back to ON, not START, but the starter continues to spin while the engine is running. Read through that and that isn't your problem because you did not energize the starter to start the current that would have caused the welded contacts to weld in the first place.

So we go after how could the solenoid close if you didn't turn the key to START? First suspect is debris (from usage) inside the ignition key switch either floating around or making a conducting path (from usage) between 12v and the START wire terminal. Or the spring return inside the switch has failed and vibration is causing it to intermittently connect the START terminal to 12v. I'd suspect that first.....a bad switch.

Second would be a chafing in the wiring harness that allowed the above mentioned function to occur somewhere in the wiring harness from the control box to the solenoid.

Third would be a failure of the spring inside the solenoid that keeps the high current plunger from closing and supplying current to the starter.

At 7 years of age I would expect the key to be the problem especially if the boat was highly used or sat out in the environment unprotected. Wiring harness chafing could happen but for that exact combination of power getting to the start wire is highly remote. Having the spring go bad inside the solenoid is a never happen event if you ask me.

Thats the best I can do from here.

 

[ahicks]

I could see how a severely corroded connection might do something like that. A look at the main engine connector might be worth your time. And taking that just one step further, disconnecting the battery until you have identified the problem might be a good idea as well. The idea of the motor starting while sitting on the trailer and out of earshot sounds pretty scary (expensive).

 

[QBhoy]

Strange problem. First off the solenoid has to energize before any power is applied to the starter motor. On solenoids ready for replacement, due to high usage, the contacts pit and the surface area is reduced so when the starting current runs through there they actually weld together and releasing the key and de-energizing the coil that activates the solenoid, the current remains because the contacts can't disengage. So you turn the key to start, the solenoid closes, the starter spins and starts the engine....you release the key and it springs back to ON, not START, but the starter continues to spin while the engine is running. Read through that and that isn't your problem because you did not energize the starter to start the current that would have caused the welded contacts to weld in the first place.

So we go after how could the solenoid close if you didn't turn the key to START? First suspect is debris (from usage) inside the ignition key switch either floating around or making a conducting path (from usage) between 12v and the START wire terminal. Or the spring return inside the switch has failed and vibration is causing it to intermittently connect the START terminal to 12v. I'd suspect that first.....a bad switch.

Second would be a chafing in the wiring harness that allowed the above mentioned function to occur somewhere in the wiring harness from the control box to the solenoid.

Third would be a failure of the spring inside the solenoid that keeps the high current plunger from closing and supplying current to the starter.

At 7 years of age I would expect the key to be the problem especially if the boat was highly used or sat out in the environment unprotected. Wiring harness chafing could happen but for that exact combination of power getting to the start wire is highly remote. Having the spring go bad inside the solenoid is a never happen event if you ask me.

Thats the best I can do from here.

Only thing I’d add to this, if it’s relevant to this engine (will be if it’s younger than 2014/15) is that I found out recently that my key ignition is unlike any I’ve had on a boat before. Normally you’d turn the key and hold until it starts. On the latest mercury outboards like this (mine is a 115 2.1l…also same basic engine as the 80-115 that age), the key is more like a start button found on cars these days. So you turn it and even if you let go an instant after, the starter keeps going until it starts. Found this out when I wanted to see if the battery was good enough to start her before launching last year. Just wanted to see if it would turn over by giving it a jag on the key…bloody thing kept going and started. Luckily I had the back end in the water at the slipway already.
So perhaps it’s the ignition that’s the issue here. Despite naturally ruling it out because it would need a sustained input and held action from the user. Not the case with mine anyway. Clearly has a smart start system.

 

[Texasmark]

Only thing I’d add to this, if it’s relevant to this engine (will be if it’s younger than 2014/15) is that I found out recently that my key ignition is unlike any I’ve had on a boat before. Normally you’d turn the key and hold until it starts. On the latest mercury outboards like this (mine is a 115 2.1l…also same basic engine as the 80-115 that age), the key is more like a start button found on cars these days. So you turn it and even if you let go an instant after, the starter keeps going until it starts. Found this out when I wanted to see if the battery was good enough to start her before launching last year. Just wanted to see if it would turn over by giving it a jag on the key…bloody thing kept going and started. Luckily I had the back end in the water at the slipway already.
So perhaps it’s the ignition that’s the issue here. Despite naturally ruling it out because it would need a sustained input and held action from the user. Not the case with mine anyway. Clearly has a smart start system.

Interesting. On the car start button I assume its a momentary SPST switch, like a spring loaded toggle that is pushed and held till the operator sees the RPMs come up or hears it running.

I can't imagine an electric circuit (requiring chips....sarcasm here) that automatically locks the solenoid shut till the electronic circuit detects RPMs high enough to signal that the engine is running. What the ......will they come up with next....self driving cars.....grin. I can see this being a big potential fire hazard if its true.

On your instance I'd bet the solenoid was severely pitted and the starting current welded the contacts shut till the engine started, taking the current load off the solenoid contacts whereby they cooled and since the joint was a "cold solder joint" type thing, the internal spring overcame the weld and it released......how many characters was that sentence....reminds me of 3rd grade grammar classes.....compound sentences.

 

[QBhoy]

Interesting. On the car start button I assume its a momentary SPST switch, like a spring loaded toggle that is pushed and held till the operator sees the RPMs come up or hears it running.

I can't imagine an electric circuit (requiring chips....sarcasm here) that automatically locks the solenoid shut till the electronic circuit detects RPMs high enough to signal that the engine is running. What the ......will they come up with next....self driving cars.....grin. I can see this being a big potential fire hazard if its true.

On your instance I'd bet the solenoid was severely pitted and the starting current welded the contacts shut till the engine started, taking the current load off the solenoid contacts whereby they cooled and since the joint was a "cold solder joint" type thing, the internal spring overcame the weld and it released......how many characters was that sentence....reminds me of 3rd grade grammar classes.....compound sentences.

Haha. You did well enough I thought . Yeah it really surprised me too. It definitely wouldn’t be corrosion. It’s a mint engine and all but showroom brand new condition all round. Certain it’s not because of an issue like that, I’d be sure. I’ll need to look up the electrical diagrams and see what’s what. That’s certainly what it did on that occasion. Was literally a 10th of a second I turned key for and it kept turning over for about 2 secs until it started. Unless it was a freak event. Don’t think so though.

 

[ahicks]

Haha. You did well enough I thought . Yeah it really surprised me too. It definitely wouldn’t be corrosion. It’s a mint engine and all but showroom brand new condition all round. Certain it’s not because of an issue like that, I’d be sure. I’ll need to look up the electrical diagrams and see what’s what. That’s certainly what it did on that occasion. Was literally a 10th of a second I turned key for and it kept turning over for about 2 secs until it started. Unless it was a freak event. Don’t think so though.

It sounds the same as a late model car. Foot on brake, hit and release the start button, and off she goes.

Betting the same circuit is found in some of those remote start accessory key FOB's. They work the same way. You don't hold the start button down on those either.

 

[QBhoy]

It sounds the same as a late model car. Foot on brake, hit and release the start button, and off she goes.

Betting the same circuit is found in some of those remote start accessory key FOB's. They work the same way. You don't hold the start button down on those either.

Yeah. That’s exactly what it’s like. Same thing on a car I have now. Was very surprised by it.

 

[Ed27518]

Hi. I have a 80hp Merc 4 stroke that has run flawlessly for the past seven years. Was a mile offshore yesterday with the engine in idle when it suddenly restarted itself. I could clearly hear the starter motor engage and then it just kept idileing like normal. Fast run back into dock and no probs with engine. At dock reverse gear was crunching and difficult to fully engage - not sure if that’s related. Engine restarted itself again at dock and a third time when I was flushing engine.

Any ideas? I’m totally stumped as seems highly unusual. Can’t get into dealer for three weeks and anxious to get back on the water!!

Thanks folks.

Mark

Could be a bad key switch. I know mine has done this, and im almost cerain its the switch.