Mercruiser 120 Coil Overheating Like Many Other Members

[Bt Doctur]

Can`t you all see how ironinc this is. The first set of points was used in the 1910 Caddy . Since then the coils on almost everything powered by gasoline have operated flawlessly, always producing the spark and not overheating .Since the advent of electronic everything people have lost the art of "repairing" . All they know is that they want it NOW.

Since most use Petronix systems and the factory suggests using 12 volts directly to the electronic `s side of this system why not do it that way. supply 12 volts on the Red wire and use the resistance wire/ballast resistor to power the coil.
You might just find that it works a whole lot better too.

 

[nola mike]

That's actually how my Mallory ignition is. Stock coil, all wiring the same. Using the resistance wire. Not sure why pertronix wants you to change out the coil and wiring

 

[lognum]

Can`t you all see how ironinc this is. The first set of points was used in the 1910 Caddy . Since then the coils on almost everything powered by gasoline have operated flawlessly, always producing the spark and not overheating .Since the advent of electronic everything people have lost the art of "repairing" . All they know is that they want it NOW.

Since most use Petronix systems and the factory suggests using 12 volts directly to the electronic `s side of this system why not do it that way. supply 12 volts on the Red wire and use the resistance wire/ballast resistor to power the coil.
You might just find that it works a whole lot better too.

And the other ironic thing is that it worked fine with points, just took longer to start sometimes. It was a local mechanic who said "why don't we change it to EI? It will work better"......go figure.

 

[lognum]

Full 12v is fed to the choke heater. A resistance wire is t-ed off the feed to the choke (at the pink arrow) and run to the coil. No resistance to the choke, resistance wire to the coil....



Here's another way of looking at it....



Chris.........

Hey Chris. One more thing, and apologies if you are repeating yourself; (See Attached Photos). here is a schematic I came across, showing the original alternator and a suggestion of how to connect the new self regulating alternator. Does it make sense to you to do this? Also, see attached a photo of the wires that are just taped off, from the original alternator, going nowhere. Any perceived issues here? Cheers,

 

[Bt Doctur]

you changed from a 3 wire to a 1 wire self-exciting unit . Just tape the unused wires

 

[lognum]

Got it. Thanks BT:joyous:

 

[lognum]

What is all the voltage reading you're seeing at the coil compared to the wire combinations you have tried? Both engine on/running and off/key on.

Do you see around 13.8 volts while the engine is running at any of the power wire connections of the engine and helm gauge?

With the black wire disconnected from the alternator, is the alternator properly grounded now? May want to confirm it is.

Since you have the flame thrower coil that is internally resistant, it reads form pretronix that you shouldn't use the resistant purple wire but ran a direct 12v wire from the key switch.

But if you go back to trying the stock coil, you can use the purple resistance wire.....Which I'm thinking the purple resistance wire is no longer working correctly so it should be measured to know for sure it's status and/or repaired if you use a stock coil at all even if it's just for testing purposes.
https://forums.iboats.com/forum/engi...49#post1336749
https://www.justanswer.com/boat/31mk...lts-times.html
Overheating igntion coil - Marine Mechanic
RESISTOR WIRE KIT (TO REPLACE RESISTER WIRE) (#84-94227A2)


http://www.pertronix.com.au/troubleshooting.html


Pertronix Flame-Thrower[SUP]®[/SUP] Coil Installation Instructions

All,

Okay, did all the tasks requested, checked all grounds, switched out the stock coil for a flamethrower coil, then back again. Same end result, 50minutes and the engine stalls out. Tried every wire combination. Tested the coils independently for functionality and both were working per spec. Did find the resistance wire was not functioning, so I took another purple resistance wire off a spare harness and spliced it in. Cut it down till I got the proper voltage at the + end of the coil. Same end result. BTW, regarding the three purple wires that run in the harness; one to the choke, one to the alternator, and one to the coil(resistance wire), if you pull them out of the harness and test them, two have no resistance and one does have resistance (obviously the resistance wire). Ran the 12v wire from the ignition, as Petronix advised, to the module (ignitor model 1146A), and left the purple and yellow purple wire on the + of the coil, same result (coil overheats). BTW, I noticed the distributor bowl and shaft were very hot to the touch, not the distributor cap). Don't know if that's an indicator of anything. Took off the distributor cap, removed the rotor, cleaned it and the contacts, same result. Took out the ignitor plate to see if there was a ground wire on the distributor bowl (there wasn't) and then ran a ground wire to the unit, as a test, same result. I am completely at a loss and so are any mechanics I speak to, but there must be a resolution. Perhaps it may take replacing the full distruor shaft and cap, as a sister boat that uses a Mallory brand runs perfect and the coil stays cool.
Does anyone know if the ignitor 1146a by Petronix is the correct one for a Merc MCM120MR? SN#A635702. Attached are a few photos of the ignitor. Thanks again.

 

[lognum]

Can Ignitor modules go bad? Would switching it to an Ignitor II part number 91146A be a solution?

 

[achris]

Yes a module can go bad. Replacing an Ignitor with an Ignitor II is a good move anyway.

Also check the distributor is properly grounded, with a ground wire. Just being bolted to the engine block is not enough (please don't ask me how I know that. :facepalm

How hot is the dissy getting? As hot as the engine block? That's normal. If it's getting VERY hot, then it may be binding up. Pull it out and check it.

Chris...........

 

[nola mike]

If it's me, I throw the points back in there to see if the problem truly is with the ignitor setup

 

[lognum]

Thanks Guys. Will check it out

 

[lognum]

Hey Chris (or others)

I just noticed (see attached pic) that he engine rotation on the Sticker plate is CCW rotation. If the Ignitor installed is 1146a, which is CW, would that be an issue?

 

[achris]

Engine rotation is CCW. Distributor rotation is CW.... That's standard...

Chris......

 

[lognum]

Thanks Chris

 

[nola mike]

Yes a module can go bad.
Chris...........

Do they go bad intermittently/after running? I've always thought these kind of electronics were go/no go.

 

[achris]

Electronics can be subject to heat failure... and intermittent failures are the hardest to find.

Chris....

 

[lognum]

Hey Chris. Can I run a ground wire from the - of the coil, to the engine, without any issue?

 

[nola mike]

Hey Chris. Can I run a ground wire from the - of the coil, to the engine, without any issue?

No, that will ground the ignition and keep it from firing.

 

[Bt Doctur]

points systems with ballast resistors were never a problem
electronic ign with full 12v power coils were never a problem
petronixs electronic systems are a problem? WHY

 

[nola mike]

points systems with ballast resistors were never a problem
electronic ign with full 12v power coils were never a problem
petronixs electronic systems are a problem? WHY

I don't think most of them are. Plenty of posts about ignition problems with points. I've had a Mallory system for 7 years without a hiccup. I agree that the points will get you home if the electronics fail, which is why my original points are rusting away in a baggie on my boat...