Mercruiser 3.0 turns over won't start

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marine59901

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Joined
May 18, 2012
Messages
6
I have a 1986 mercruiser 140 3.0 that has really been frustrating me. I have checked for fuel and it is getting fuel. I have replaced the coil, coil wire, points, dist cap, rotor, condensor and still nothing. I have 4 wires going to the coil on the positive side I have a purple wire that looks like it goes into the main wire harness and I have a purple with yellow that goes to the starter. On the negative side I have a grey wire that I assume is the tach wire and than a black wire that goes to the dist. I get a full 12 volts to the positive when key is on and get 7.5 to 8 when you try to start it. I removed the grey wire and still doesn't start. I have charged the battery I have checked the ign switch and all seems to be fine. I hooked up a spark plug to the coil and ground it to check for spark and I couldn't see any not sure if It would but tried anyway. I checked for rest on the coil with all wires unhooked and got rest. I am really stuck and would like to know what to try next. I don't have a history on the boat we bought it in the winter but it was prof winterized. Good lesson to look for boats when you can start them up lol but any help would be greatly appreciated.
 
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Lyle29464

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Mar 10, 2009
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Re: Mercruiser 3.0 turns over won't start

I would unhook all the coil wires except the black to the dist. Then jump a hot wire from the battery + to the + on the coil. Try that. It may tell you where your problem is.
 
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marine59901

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Joined
May 18, 2012
Messages
6
Re: Mercruiser 3.0 turns over won't start

Lyle29464 said:
I would unhook all the coil wires except the black to the dist. Then jump a hot wire from the battery + to the + on the coil. Try that. It may tell you where your problem is.
Click to expand...

So I did that and 12v at the + side of coil and get .65 on the - side. I unhook the black wire going to dist and I have 12v on the - side is this possibly a grounding issue on the dist and what would I look for. I also unhooked the condenser wire just to see and that still gave me .065v on the neg. I switched back to the old point and tried everything again and same thing.
 
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Lyle29464

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Re: Mercruiser 3.0 turns over won't start

With your points open you should have 12 volts on the + side of coil and the - side of coil and and on the moving side of the points. Plus the coil should have fired when you opened the points. With points closed you should read the drop of the resister wire so you will have about 7 volts at the + side of the coil and almost nothing at the - side. When you turn the Key to start you should get 12 volts from the starter to the + side of the coil. As your turning the engine over the volt meter should vary from 7 to 12 volts as the points open and close. The coil should be firing.
 
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marine59901

Cadet
Joined
May 18, 2012
Messages
6
Re: Mercruiser 3.0 turns over won't start

Lyle29464 said:
With your points open you should have 12 volts on the + side of coil and the - side of coil and and on the moving side of the points. Plus the coil should have fired when you opened the points. With points closed you should read the drop of the resister wire so you will have about 7 volts at the + side of the coil and almost nothing at the - side. When you turn the Key to start you should get 12 volts from the starter to the + side of the coil. As your turning the engine over the volt meter should vary from 7 to 12 volts as the points open and close. The coil should be firing.[/QUOTE

So I checked it when the points are closed and the volts were low when the points are open then it goes to about 8 volts. The points when closed showed 12 volts and when i open them with a screw driver the points spark.
Click to expand...
 
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marine59901

Cadet
Joined
May 18, 2012
Messages
6
Re: Mercruiser 3.0 turns over won't start

Lyle29464 said:
With your points open you should have 12 volts on the + side of coil and the - side of coil and and on the moving side of the points. Plus the coil should have fired when you opened the points. With points closed you should read the drop of the resister wire so you will have about 7 volts at the + side of the coil and almost nothing at the - side. When you turn the Key to start you should get 12 volts from the starter to the + side of the coil. As your turning the engine over the volt meter should vary from 7 to 12 volts as the points open and close. The coil should be firing.
Click to expand...

So I checked it when the points are closed and the volts were low when the points are open then it goes to about 8 volts. The points when closed showed 12 volts and when i open them with a screw driver the points spark.
 
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