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4.3 Mercruiser won’t crank

J

JRemington

New member
I uncovered the boat today, put a muffler on it and she started right up. I shut her down and took her down to the boat launch, backed her into the water and she wouldn’t turn over. I checked and have 12.6 volts at the starter. The problem is with the switch held in the crank position there is no voltage in the wire at the solonoid. I have been reading about a shift interruptor switch. Could this switch being bad cause this issue? The boat is a 1988 StarCraft Islander with a 4.3 Mercruiser. Any help would be appreciated.
 
First, You are saying it will not crank over at all?

If so then First guess is Slave solenoid.


The interrupter switch ONLY interrupts the ignition which would not allow it to START if the switch is depressed/closed. It's use is only when shifting OUT OF GEAR on a Alpha drive. ONLY! If the interrupter switch fails in the closed position then the engine will not start due to loss of Ignition but it would crank over and over until battery is dead.


Below is the schematic, In section B Item 6 id the slave solenoid. This is a common failure.

V6 TBIV wiring.JPG
 
Thank you. Everything else on the boat works, but when I turn the key to the start position it’s completely dead. No click or anything. Are you talking about the solonoid connected to the top of the starter? Thank you
 
I changed the solonoid and it still doesn’t turn over. I pulled the switch and I have power at the red power wire and no voltage at the yellow wire with a red stripe. If I hold the key in the crank position I still have no power at the yellow and red wire. Shouldn’t jumping the red and yellow wires crank the engine over?
 
Then it is either a bad connection in the wire harness or it is the key switch.

Note key switch connection (take photo) remove wires and pull switch and using ohms on metter check to see if you have continuity from battery post to crank post and run post when key is in the respective positions.

is your shifter in Neutral?
The crank wire yellow with red stripe goes thru the neutral safety swith in control box.
 
Further... " is your shifter in Neutral?" Sometimes mechanical wear or loose switch mounts will make it necessary to "wiggle" the shifter in neutral to get it to start.
 
sandkicker said:
Further... " is your shifter in Neutral?" Sometimes mechanical wear or loose switch mounts will make it necessary to "wiggle" the shifter in neutral to get it to start.
Click to expand...
Yep could be a bad neutral safety switch which is down stream of the key switch…
 
Well, it’s fixed for the time being but I don’t know for sure what it was. I was testing wires and I decided to check for power at the yellow wire on the switch with the key in the crank position. I was holding it in the crank position and as I was about to rest the wire all of a sudden it started turning over. If I had to guess I would say there was something in the switch that finally got the connection it needed. I didn’t touch the shifter so I don’t think it was the neutral safety switch. I think for $20.00 I’ll put a new switch in. Thank you everyone. Boats, lol.
 
Most boat ignition switches are at best medium quality.
Most are simple 3 position switches and only last so long.

In my boat i have a higher quality all brass type and i have had to replace it.

I tested it out of the boat with a meter and found one of the riveted connection where the wire leads connect had bad contact.... unable to service that connection point on switch and had to replace the whole ignition switch...

Also be aware, many wire harnesses that connect to dash have a connector which separates the main harness from the dash. This is also true at engine. (Large black connector)

If you have this and can find this dash harness connector its good to have a look, unplug it and look at pins and sockets and plug back in. Maybe a few times to ensure good contact with pins and sockets....
 
These 4.3’s are causing me problems this year. I have a 20 foot Thompson with the same engine. I put batteries in it today and when I turn the key to the crank position the slave solenoid clicks. Nothing else. I have 12.7 volts at the top of the solenoid with the big red wire. Then with the key in the crank position I have 9.6 volts on the small yellow wire at the slave solenoid but 11.1 volts at the solenoid on the starter. Doesn’t the yellow wire from the slave run directly to the starter solonoid?
 
?Basic marine starting system
From the key in start position power thru the shift interlock in the control box, then thru the small yellow/red to the slave. The large lug with the Red/purple is always hot, the large yellow/red goes to the starter solenoid. the small yellow/red comes from the key switch and the most important wire left is the Black wire. this supplies a ground for the solenoid to work.
If jumping the large lugs cranks the engine battery and power connections are good.
If key does nothing, check for power at the Red or Orange wire at the key switch.Turn key to "ON" power to the purple wire at the key switch. Turn key to "START" power to the yellow/red at the key switch. If this is correct locate the harness plug at the engine.and check its connection for damage.
 
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