2005 Mercury 115 ELPTO Intermittent starter issue

[Nathan Bond]

Having some intermittent starter issues with my boat.

When the engine is cold, the starter will either a) crank normally or b) very, very slowly crank.
No way to determine which it will do, turn it over 10 times and it's fairly random which will happen.
Sometimes, it was start cranking slowly, then after 5 or 6 slow cranks, speed up to normal.
Once the engine is warm/hot, it's almost always slow crank.

I've tried it with 4 known good batteries, 2 of which are brand new.

I went through some of the troubleshooting steps in the FAQ, and here are the results/measurements.

Battery before cranking: 12.9 volts

When starter cranks normally:
Battery voltage while cranking: 11.5 v
Starter Positive Terminal/Engine Ground: 10.2 v
Solenoid Input/Engine Ground: 10.2

When slow cranking:
Battery voltage while cranking: 10.5 v
Starter Positive Terminal/Engine Ground: 8.4 v
Solenoid Input/Engine Ground: 8.v

After very little cranking overall (maybe 4 to 5, 5-10 second cranks to take measurements), the starter will warm up and and it's always a slow crank after that.

In fact, with both fully charged batteries on (I have a 2 battery switch), it will slow crank with both batteries in circuit, once the starter gets warm.

Time to replace the starter? I would think it were corroded cables, it wouldn't crank normally at all.

 

[Silvertip]

Before you spend money on a new starter, why not disconnect and clean (shiny clean) every battery cable including those at the switch and the ground cables on the engine and batteries. Don't forget the +12 volt cable going to the starter solenoid and cable between the solenoid and the starter. After that you can repeat the voltage measurements and compare them with what you observed before. If they now differ and things work well, do your happy dance. If not, pull the starter and have your local starter/alternator rebuilder test it and rebuild it if necessary. And even before that, pull the plugs, disable the ignition by pulling the kill switch lanyard and see if the starter can spin the engine freely. If it can't, the problem is NOT the starter but possibly a tight lower unit.

 

[Nathan Bond]

Before you spend money on a new starter, why not disconnect and clean (shiny clean) every battery cable including those at the switch and the ground cables on the engine and batteries. Don't forget the +12 volt cable going to the starter solenoid and cable between the solenoid and the starter. After that you can repeat the voltage measurements and compare them with what you observed before. If they now differ and things work well, do your happy dance. If not, pull the starter and have your local starter/alternator rebuilder test it and rebuild it if necessary. And even before that, pull the plugs, disable the ignition by pulling the kill switch lanyard and see if the starter can spin the engine freely. If it can't, the problem is NOT the starter but possibly a tight lower unit.

I did actually clean, scrub and measure the resistance of all the cables before posting. I also pulled the plugs and spun the flywheel by hand to make sure wasn't any undue tightness in the engine. I didn't post until I had read hours and hours worth of posting on the subject so I wouldn't sound like an idiot .

 

[Nathan Bond]

And... it was the starter. Installed an aftermarket one from DB Electronics and it cranks like a champ.

 

[Texasmark]

Well that was the question on warming up and having problems plus your 8 volts on the input side of the solenoid. Was it low current due to bad connections between the battery and the solenoid, or was it a shorted starter drawing too much current causing the low voltage reading.

Glad you got her fixed.

Mark