Modified Breakerless Electronic Ignition Question

[San_Diego_SeaRay]

Engine: 1981 Mercruiser MCM 260
Ignition: Originally a Mallory "points" type ignition but modified to an electronic distributor using a Pertronix Ignitor 2 (PNX ML-181) kit as well as a 3 ohm Flamethrower coil


So today was supposed to be the big day after months of toiling on rebuilding this engine from a heap of rust into a useable engine. When I spoke to the previous owner last November, he told me that he was in the process of rebuilding the boat himself when he gave up. One thing he said he did do was upgrade the ignition to "points" type ignition to electronic ignition. I had to do some detective work, but I've pretty much been able to determine what he did, which I described above.

So today I finally install all the spark plugs and wires. It's a 12V coil, so I skip the resistance wire and just clip a 18 gauge alligator clips to the "+" side of the coil and to the "- "side of the coil, with each going directly to the BAT and GROUND, respectively. I turn over the engine a bunch of times. Nothing. Then I put an inline ignition spark checker between the coil output wire and ground. There's a spark when I start turning over the engine, then a spark when I stop turning over the engine, but nothing in between. After about a minute of turning the engine over, I notice the alligator clip wires are warm. Then I touch the coil. Hot. I'd say about 140 degrees. You couldn't put your hand around it for more than 15 seconds.

So I've got a hot coil and an intermittent spark. What do you guys think?

 

[wrench 3]

The heating problem is from the negative jumper going directly to ground. It needs to be controlled by the electronics which grounds it intermittently to produce the spark. On most electronic conversions there are two wires from the distributor. One to each side of the coil. Then you connect 12v to the coil +.
I'll check on the wiring for your system and get back with it, if no one else beats me to it.

 

[wrench 3]

The wiring instructions show a red and a black wire coming from the distributor. Red to coil + and black to coil -. Plus a 12v to the coil +.

 

[San_Diego_SeaRay]

The wiring instructions show a red and a black wire coming from the distributor. Red to coil + and black to coil -. Plus a 12v to the coil +.

Hmmm...thanks. My distributor does have one red wire and one black wire coming out of it. But none of my diagrams in my Service Manual ever showed a red wire, just a black one. And since mine was modified I was kind of puzzled how it went.

But the reason I thought you could just wire the "-" to ground is that the wiring diagrams show a gray wire coming off the coil "-" to the shift interrupter, then to ground. So I thought the shift interrupter was "always on" (completed to ground) and when you shifted, that connection to ground was broken and the coil temporarily lost it's ground. But maybe it works the opposite: Maybe when you shift, it provides a "short circuit" ground thru the shift interrupter which causes the coil to become "static" and so the windings can't collapse and induce a spark? Does the shift interrupter break a circuit or does it complete one?

On a related note, if you're right, that means that the distributor is probably grounded to the block? Uh oh. I bought a gasket set that included a million little gaskets and I didn't know where they all went. One of them was ring shaped and fit perfectly at the base of the distributor. So of course I put it there, thinking the black wire would do all necessary grounding.

EDIT: Oh maybe you looked up the Pertronix Ignitor 2 wiring instructions? I thought you were talking about the Mercruiser instructions. Whoops. But I think you nailed it about how these conversion kits are wired. :rockon:

 

[Fed]

But maybe it works the opposite: Maybe when you shift, it provides a "short circuit" ground thru the shift interrupter which causes the coil to become "static" and so the windings can't collapse and induce a spark? Does the shift interrupter break a circuit or does it complete one?

Correct, the shift interrupter shorts the negative side of the coil to ground when the cables strain which stops the magnetic field in the coil expanding & contracting in time with the points.

 

[San_Diego_SeaRay]

Correct, the shift interrupter shorts the negative side of the coil to ground when the cables strain which stops the magnetic field in the coil expanding & contracting in time with the points.

OK cool; I'm so happy to understand more and more how all the wiring works. Makes owning a boat more fun.

Well thanks Wrench and Fed for the replies. I think re-wiring the coil like Wrench advised is gonna solve the problem. Unfortunately I also found a leak in the starboard riser/manifold joint so I'll have to address that prior to starting the engine. But I'll report back as soon as I try again to get it started.

 

[wrench 3]

Sorry I didn't get back to you last night but it got past my bed time. We're on eastern time.
The distributor does ground through the base. A gasket is normal under the distributor mount but the clamp holding the distributor in position will provide an adequate ground.

 

[San_Diego_SeaRay]

Well Wrench thanks again for the tip about wiring the ignition. I fired her up last night and she wheezed and spat and coughed and choked but she fired up and ran for 5 minutes before I killed the experiment. Then I researched carb adjustments and fired her up again today after turning both idle screws in about 3 full turns. She's gonna be a keeper now. Now she's just a few minutes of fine tuning from being a purring kitten. I'll tackle that next week. But just wanted to provide an update.

Here's a clip from last night before my adjustment today w. my neighbor handling throttle duty:

[video]http://vid1258.photobucket.com/albums/ii528/JCARREOLA/Public%20Folder%20created%20by%20JCA/MVI_2479.mp4[/video]

 

[wrench 3]

Thanks for the update. It sounds like you've got great start to a good running boat.
Have fun.

 

[justinfaith]

Hey guys, I a newbie here but I have a question along the lines of this forum. I've got a recently acquired '84 mercruiser 3.0. When I got the boat, the black wire from the coil was just sitting loose in the distributor cap (points). Just need to know where to attach it! I can't find any pics or info... Thanks a bunch!

 

[wrench 3]

Hey guys, I a newbie here but I have a question along the lines of this forum. I've got a recently acquired '84 mercruiser 3.0. When I got the boat, the black wire from the coil was just sitting loose in the distributor cap (points). Just need to know where to attach it! I can't find any pics or info... Thanks a bunch!

Number one: welcome to iboats.
Number two: next time open a new thread for your problem.
Number three: go to http://boatinfo.no/lib/mercruiser/manuals/mercruiser3.html#/232 and enter page #233.

 

[justinfaith]

Thank you, Sir!