3.0 Mercruiser with Pentronix ignition

[02torched]

Having some trouble and was hoping someone could chime in with some advice. I have a 3.0 Mercruiser with the pentronix ignition system. The boat won’t start. I’m getting spark however the spark looks extremely weak to me. I’ve checked voltage at the coil and from the + side of coil to ground I’m getting 6.7 volts with the key on. From my understanding I should be getting the full 12v with this system. I have noticed that if I take the black wire coming from the distributor off of the - side of the coil then I get the full 12v to the coil. Is this normal?

 

[Scott Danforth]

the black wire is the wire from the pertronix

the grey wire is your tach

the + side connection may be 9 volts (with resistor wire) or may be aprox 12 volts (without resistor wire) depends on the coil used

here are the instructions http://www.pertronix.com/docs/instruction-sheets/1181.pdf

 

[greno]

I did a Pertronix conversion on mine about 10 years ago and I remember needing to get a new coil plus having to make sure I had +12v at the coil. The +9v didn't cut it.

 

[02torched]

the black wire is the wire from the pertronix

the grey wire is your tach

the + side connection may be 9 volts (with resistor wire) or may be aprox 12 volts (without resistor wire) depends on the coil used

here are the instructions http://www.pertronix.com/docs/instruction-sheets/1181.pdf

Thanks for the response. The Pertronix conversion was done by the previous owner and the boat ran fine after so I believe the install was done correctly. The fact that I have 12v to the + side of the coil until I connect the black wire from the pentronix to the - side of the coil just doesn’t make sense to me. As soon as I can next that wire my voltage to the +side of coil drops to 6v.

 

[Scott Danforth]

if you have a bad connection on the + side and a slight load from the pertronix unit, you would see voltage drop.

so either the pertronix unit is fine and you have a bad connection somewhere or the pertronix unit is bad and pulling the whole system down. i believe you have a bad connection.

 

[02torched]

if you have a bad connection on the + side and a slight load from the pertronix unit, you would see voltage drop.

so either the pertronix unit is fine and you have a bad connection somewhere or the pertronix unit is bad and pulling the whole system down. i believe you have a bad connection.

So if I put a jumper wire straight from the + battery to the +side of the coil and still only got 6v when the black wire was connected from pentronix to the -side of the coil that would lead you to believe the pentronix unit is bad?

 

[Scott Danforth]

So if I put a jumper wire straight from the + battery to the +side of the coil and still only got 6v when the black wire was connected from pentronix to the -side of the coil that would lead you to believe the pentronix unit is bad?

with that big of a load to drop voltage that far, you should see smoke and fire. something has to be getting hot.

check your battery cable connections, specifically the ground cable on both ends (block and battery). I bet you find corrosion.