Ignition Coil / No Spark Issue

[Milkman38]

Never had issues with my boat until this year, thanks to these great forums I was able to fix it myself. But, working on a friends boat now and I'm stuck.

Working on an '87 3.0l Mercruiser. Started with bad gas, I have fixed that situation but the boat will not fire at all. I have read and read in these forums different things to check and try and there are so many I'm getting confused and not sure if I'm doing any of the diagnostics correctly.

Without further ado, I am attempting to establish if the boat even has any spark. I started with the coil. Key on, both terminals have battery voltage (13+), when engine cranking voltage drops to 9 on both sides of the coil. I have removed the purple wires from the + side, hooked battery directly, no change. I have also disconnected the momentary shift/kill switch wire... no change. I have put a plug into the main coil wire to the distributor, no spark at all. Is this enough to warrant replacing the coil? Have I missed a step or a test?

I have read many helpful posts in here and I have also read posts where people have the same issue and have thrown good money after bad and are still parked in the driveway. Trying to avoid that.

 

[Milkman38]

Again... still reading. Am I looking for spark from the coil? I pulled the main out of the distributor and put a plug in there.. no spark. Thinking I've done it backwards. Also did the old fashion way removed plug from engine and ground it... again no spark. Its been a long time since I touched anything with a distributor, but I'm assuming I need to take the cap of next and see whats going on inside?

 

[gm280]

:welcome: Milkman38 to iboats. Nice for you to join us...

Okay, first, no coil is going to work with straight 12 DC connected to it. Reason? because a coil (transformer is a better nomenclature for it) can only work with either AC current or pulsed DC. The build up of voltage and current and collapse of it is how it transfers energy from the primary side to the secondary side. So it won't work with straight DC voltage. So don't run out and order a new coil...just yet. Sounds like your problem is whatever is feeding that coil. Whether that is on the positive side or negative side, You have to have a pulsed voltage for it to work. So look at what drives your coil as the source of your problem... I have no idea how your engine ignition is designed and therefore have no suggestions other then the ignition box or control...

 

[Bt Doctur]

is it a points system or electronic? If points, they need to make contact when they open and close. they need a gap of .018
with your meter on the neg side of the coil, the voltage should pulse if the points are opening and closing as they should.

 

[Bondo]

Its been a long time since I touched anything with a distributor, but I'm assuming I need to take the cap of next and see whats going on inside?

Ayuh,..... Exactly,..... There's probably points in the distributor, which are what fires the coil,.....

 

[Milkman38]

Thanks gentlemen !! Its starting to come back to me now. As soon as this monsoon ends (Southern Ontario) I'll see what's going under the cap.