Ign. questions

[LuckyPenny]

I have spent most of the springtime doing what most of us do. pour money into the hole in the water. But now I have a question about the ign system. I replaced the coil. the old one failed (oil leaked out) I followed the suggestion of a tech I know and installed one that has an internal resister. I am getting the following readings. On the "+" side 12.4 volts<br />on the "-" side 3.8-4.2 volts. I remember reading somewhere that the neg side should be ~7 volts. did I install the wrong coil. The nercruiser manaul for my year boat (1977) shows a resister wire. What is it and where is it?<br /><br />Thanks

 

[achris]

Re: Ign. questions

LP,<br /><br />You can't use an 'internally resisted' coil on these engines without running a new wire to the coil. The resistance wire is in the harness and looks just like any other wire. <br /><br />Sounds like the 'tech I know' knows little about Mercruiser marine engines and their wiring. Just go back to the shop and buy a coil that has the words (or words to the effect) "To be used with external resistor".<br /><br />If the voltage reading on the points side of the coil (with the points closed) is anything other than 0 volts, you have a points problem. <br /><br />How much do you understand about electrical circuits? If you treat the ingnition system as a DC system and try and measure volts in the static situation the readings are invalid. If you have a 12 supply to a resistor (in this case only about 4 ohms) then through a coil (very close to 0 ohms) and finally to ground (through closed points), then the voltage readings will be low on both sides of the coil. If the points are open, then the voltage on each side of the coil will be the same, about 12 volts. You need to understand that the system only works properly in a dynamic situation. This link has a reasonable explanation of the theory of it all Theory of ignition systems <br /><br />Hope this helps,<br /><br />Chris............

 

[LuckyPenny]

Re: Ign. questions

with the key in the run I get 0 volts at the "-" post. The readings are take with the key in the start position (cranking)

 

[achris]

Re: Ign. questions

The readings are take with the key in the start position (cranking)

Sorry, I didn't see that in the original post, silly me <br /><br />To answer your original question

did I install the wrong coil

Yes.<br /><br />Have you tried with a "use with external resistor" coil?<br /><br />Chris.........

 

[jeff13601]

Re: Ign. questions

The resistor wire should be purple and should also come to the positive side of the coil. If your manual is right you should have a coil that says " use with external resistor". This resistor wire should drop your voltage to about 8 volts or so on the positive side of the coil, but if your book is correct you now have two resistors.