Hard to start unless starter solenoid is shorted

[morebacon]

I'm dealing with this weird situation where the boat is hard to start when using the key, but if I short the 2 main slave solenoid terminals it fires right up. When using the key, the engine cranks fine, but I can barely get it to start after a lot of retries. I checked the small solenoid terminals and I get 12V when the key is on START. Mercruiser 3.0, if that matters.

I have recently replaced the starter solenoid. Checked and cleaned all connections - battery, starter, solenoid, circuit breaker, etc.

Any suggestions on what I should check next?

 

[Scott Danforth]

Clean your connections

 

[nola mike]

I'm dealing with this weird situation where the boat is hard to start when using the key, but if I short the 2 main slave solenoid terminals it fires right up. When using the key, the engine cranks fine, but I can barely get it to start after a lot of retries. I checked the small solenoid terminals and I get 12V when the key is on START. Mercruiser 3.0, if that matters.

I have recently replaced the starter solenoid.

The slave or the actual starter solenoid?
Sounds like your wires are getting hot from a bad connection, increasing the resistance more. When you've tried starting with the key and it's having trouble, does it still start right away when you jump the slave? And by hard to start, you mean it isn't turning over quickly, right?

 

[morebacon]

The slave or the actual starter solenoid?
Sounds like your wires are getting hot from a bad connection, increasing the resistance more. When you've tried starting with the key and it's having trouble, does it still start right away when you jump the slave? And by hard to start, you mean it isn't turning over quickly, right?

Replaced the slave, sorry for the confusion. Jumping the slave posts immediately starts it, it doesn't even do a full turn. When using the key it's cranking and turning over for a long time, or it takes 7-8 tries to get it to start.

Clean your connections

Thanks, I'll have another go at it tomorrow - cleaned and tightened all battery and starter wires, grounds, even used an electronic spray cleaner...

 

[Scott Danforth]

Replaced the slave, sorry for the confusion. Jumping the slave posts immediately starts it, it doesn't even do a full turn. When using the key it's cranking and turning over for a long time, or it takes 7-8 tries to get it to start.


Thanks, I'll have another go at it tomorrow - cleaned and tightened all battery and starter wires, grounds, even used an electronic spray cleaner...

electronic spray cleaner is to wash away dirt from a TV tuner, not remove corrosion from battery cables

use sand paper or a wire brush chucked in the drill

the connections should be shiny and clean enough your mother in law will eat off them

once completed, then seal every connection with marine electrical varnish

 

[kenny nunez]

Do you have a points ignition or the later Mercruiser electronic?

 

[morebacon]

the connections should be shiny and clean enough your mother in law will eat off them

once completed, then seal every connection with marine electrical varnish

I did that today, wire-brushed and sanded down to shiny metal all the connections. But still the same problem Here's a cold start video, once I touch the jumpers it immediately starts up...

https://imgur.com/a/wZCZTUO

Do you have a points ignition or the later Mercruiser electronic?

No points, the newer electronic one (I think).

 

[Scott Danforth]

check for spark when you are cranking

 

[stang32]

check for spark when you are cranking

yes, also the ignition switch may be bad and not allowing power to the rest of the electronic system when turned to crank. check for power at the coil or if you cant get to that, check power to the choke while cranking from the key. they are on the same circuit.
does the tach move while cranking?

 

[nola mike]

check for spark when you are cranking

Yeah, losing voltage to the coil when cranking. Only place that can happen that I can see is at the ignition switch. What do your gauges do while you're cranking?

 

[nola mike]

yes, also the ignition switch may be bad and not allowing power to the rest of the electronic system when turned to crank. check for power at the coil or if you cant get to that, check power to the choke while cranking from the key. they are on the same circuit.
does the tach move while cranking?

Ha ha, nice response. My thinking exactly

 

[poconojoe]

Heres a long shot:
Sometimes cables themselves can go bad with internal corrosion.
I had this happen on a truck years ago.
One of the battery cables looked a little melted at the battery. I cut it back and there was all green corrosion between the strands.
Got a new cable and all was well.
I think the fact that marine wiring is tinned throughout it's entire length helps prevent this. But, if someone replaced any wiring with non-marine standard, this might happen.

So not only clean the connections, but take a close look at the condition of the cables themselves.