Mercrusier 170 runs fine but randomly won't start

[Ahill11]

Hey all,

I have a mercrusier 170 in my Thompson (80's model) it'll start fine and run fine cold hot etc. sometimes tho it won't want to crank, such as sitting in a lock for 15 mins I'll be in neutral and nothing happens, then I wiggle handle get pissed and them sometimes will crank extremely slow and sometimes crank fine. I jumped the start before directly with a battery and it started fine. But after being stuck at a dock over night the next morning stepped in and she fired right up and ran her two locks home no issue. My question is does this seem like a switch problem or starter/selanoid or somethings completely different. Battery and connection are all good tight and enough CCA. Any guidance is appreciated.

 

[Bondo]

Ayuh,.... Welcome Aboard,..... Take apart yer tight wirin' connections, 'n clean 'em to shiny metal Clean, 'n put 'em back together,....

Sounds like ya got a corroded connection or 2 in the startin' circuit,.....

 

[ihc1470]

What do you have in the way of test equipment? And which trouble shooting method would you like to use SWAG or WAG? Do let us know on test equipment such as voltmeter or test light.

 

[Bt Doctur]

dont know of locks in the us so guessing your abroad. do the gauges work with the key on? If yes you have power to the dash and and a no crank condition could be the neutral safety switch in the control box. you should see 2 yellow wires coming from the box for testing cut them and slice them together ,not the wires coming out of the control box,the other end.
Slow cranking is a battery problem, a starter problem, a starter solenoid problem, battery cable or cable end problem, or an overheated starter motor

 

[Ahill11]

I have a volt meter and test light. Test light is perferred ihc1470.

Bt Doctur- its on a river with dams so we have to lock up and down, i just notice it most there because i shut the boat down when in them. Gauges all work with key, battery is brand new. The neutral safety switch where is that located exactly? Because i know there is a neutral interrupter switch as well...

 

[Bt Doctur]

the "no start in gear" switch in is the control box, prevents the motor from cranking if the handel is not in neutral. If the switch goes bad or is heavy with the grease it wont work properly and prevent you from cranking the motor

 

[Bondo]

I have a volt meter and test light. Test light is perferred

Ayuh,.... Welcome Aboard,..... When it won't start, check for power into, 'n out of the slave solenoid,....

Then check the starter's solenoid,.....

When ya turn the key to Start, that energizes the slave solenoid, which energizes the starter's solenoid,....

 

[Ahill11]

Bt thanks for the suggestion I'll look at it this weekend and try to role that out, or fix it if it's the problem.

Bondo where is the slave solenoid located? I know where the starter one is lol

 

[nola mike]

Slave is on the port side of the block, to the front and above the starter, just below the exhaust manifold. Trace the (orange/yellow?) wire from the starter back. The early 470's didn't have a slave though.

 

[mr 88]

dont know of locks in the us so guessing your abroad. do the gauges work with the key on? If yes you have power to the dash and and a no crank condition could be the neutral safety switch in the control box. you should see 2 yellow wires coming from the box for testing cut them and slice them together ,not the wires coming out of the control box,the other end.
Slow cranking is a battery problem, a starter problem, a starter solenoid problem, battery cable or cable end problem, or an overheated starter motor

FYI -There are locks on the Erie Canal which empty into the upper Niagara River and 7 miles upstream of that point is another set of locks on the Niagara River to get sail boats/barges etc under the Peace Bridge where the current is 12 mph. I think there might be some in the Chicago area as well. Try googling it and see how many you come up with.

 

[JerryIrons]

If it were my boat I would go through the cables and connections like bondo said and clean them all nice and shiny. Also clean up any grounds as well.

 

[iand464]

dont know of locks in the us so guessing your abroad. do the gauges work with the key on? If yes you have power to the dash and and a no crank condition could be the neutral safety switch in the control box. you should see 2 yellow wires coming from the box for testing cut them and slice them together ,not the wires coming out of the control box,the other end.
Slow cranking is a battery problem, a starter problem, a starter solenoid problem, battery cable or cable end problem, or an overheated starter motor

Plenty of locks on the upper Mississippi first one is in Minneapolis.

 

[Davetowz]

Toss a timing light in the boat. Next time it is struggling check the timing. I had mechanical advance hanging up on my 3.7 and it would intermittently crank very hard. I redid the entire power side and ground side wiring and still had the issue, found the real issue on a fluke.