Puzzling problem - Mercruiser straight six

[Fishermark]

Sorry in advance for the long post... Hang in there to the end and see if you can give me any direction!

My dad called me this morning with a problem he was having on his boat. First a little background.... This is an early 70's 165 Mercruiser - straight six with an aftermarket alpha clone outdrive. This is the same engine I rebuilt for him last year. More details on the engine, etc are here:
http://forums.iboats.com/showthread.php?t=236240

Anyway, he said after coming in from fishing last week he went to flush the engine when he returned and the starter just clicked or chattered. He suspected maybe the battery cables were corroded, so he took them off. When he took the cable off the starter, he broke the solenoid. He took the starter off and took it to the local shop, they put a new solenoid on for him. When he went to hook the wires back up he got a big spark every time he tried connecting the wires. At this point he calls me.

Long story short... or at least shorter.... here's what I have done and discovered so far:

I began unhooking the various wires and plugs, then reinstalling them one at a time to see what was causing the spark - or short. Narrowed it down to the alternator. With everything else connected, EXCEPT the big red wire at the back of the alternator, there is no problem. When we try to connect the wire to the alternator there is a big spark.

Okay I think to myself: Problem solved. That would even explain why the battery was down after running the boat for the day. Figure the alternator is shorted out inside somehow. We will be taking that in for testing and rebuilding or replacing.

Here's where it gets weird....

With the alternator removed and the big wire at the back completely disconnected, I tried starting the engine to flush it;. Wouldn't start at all - starter turns, engine spins fine, just does not start. We notice smoke coming out of the distributor. Took the cap off and the Pertronix Ignitor II module is burned and melted. Not good.

Put the points back in and try to start the engine. Same thing... EVEN TO THE SMOKE FROM THE DISTRIBUTOR! Remove cap again - points are so hot that I burn my finger when I touch them. (This is only after five to ten seconds of trying to start the engine).

Well, the only thing that the points are connected to of course is the coil. It is a Pertronix Flamethrower coil. I put a different coil on and let the points cool off. Engine starts right up.

What the...!

He wants to put a new Pertronix unit in - which I'm glad to do... BUT... I need to know what caused what? Did the alternator cause the coil program? Or visa versa? It can't be a coincidence. Anyone shed any light on this problem?

 

[MikDee]

Re: Puzzling problem - Mercruiser straight six

It appears to me that you have a Bad Ground condition somewhere!? It could be as simple as the coil ground, or a bad engine ground somewhere. The single red wire going out of the alternator, is just used to charge the battery usually, maybe the battery ground is bad somewhere? Also the distributor, is supposed to be grounded by it's base to the engine block, (to produce spark) and the engine block is supposed to be grounded, if their is a fault in the ground there, I could understand the Dizzy getting hot inside. I know it's crazy how things happen sometimes

 

[chiefalen]

Re: Puzzling problem - Mercruiser straight six

You cant mix and match the coil and electronic ignition. Points old style round coil.

Electronic ignition the the coil that goes with it.

And i know everyone raves about electronic ignition, i have old style points old style coil.

Could have the setup for nothing sitting in my friends garage.

 

[MikDee]

Re: Puzzling problem - Mercruiser straight six

After re-reading your post, I'm thinking you need the red wire attached to the alternator, so that it completes the starting/running/charging circuit, without it, it's causing a sort of flashback of electrical current that will fry odd items as you see. If it's sparks when you try to attach it, it could be grounded out somehow at the battery, or solenoid, is it on the right terminal connection there? Silly question now, Is the battery hooked up right, the right polarity? it's not backwards is it?

 

[chiefalen]

Re: Puzzling problem - Mercruiser straight six

Never thought of that.

Grounding the pos. cable.

My hat off to you sir.

 

[Fishermark]

Re: Puzzling problem - Mercruiser straight six

No. The battery is hooked up correctly. And once I changed to another coil it started up with no problem.

Chief - The coil that went bad (and I am assuming it is bad) is designed for the electronic ignition. After burning up up the module and nearly burning up the points I put another coil on. It too is designed for the Pertronix module in that is does not require external resistance. The points were just put in to see if it would run.

By the way, if there are any electrical engineers out there, here is the wiring diagram for this engine. Note it has the ammeter gauge and it is still in use.

 

[chiefalen]

Re: Puzzling problem - Mercruiser straight six

Electronics not my best suit, however the wire is the resistance. I wish you were close here i would give you a coil i have 3 extras.

Those are hotter coils i think meant to be used just for the electronic conversion.

Like i said i could get the electronic conversion for nothing and my friend would install it for me and i just like the old style points system better.

I know, i know people are gonna jump all over me how they get better performance and they last forever.

However time and again you will read about all sorts of problems such as yours.

The system is just not forgiving.

 

[Fishermark]

Re: Puzzling problem - Mercruiser straight six

Electronics not my best suit, however the wire is the resistance. I wish you were close here i would give you a coil i have 3 extras.

Those are hotter coils i think meant to be used just for the electronic conversion.

When I rebuilt this engine last year I installed the electronic conversion myself and installed it according to the directions. I have installed a few of these with no problems - this is the first problem I have encountered and it seems to be unusual - at least to me! And I still don't know if the alternator problem caused the coil problem or if the coil problem caused the alternator problem. Or if a yet undiscovered problem caused both.... Or if they are completely unrelated! (Which I do not believe).

Regarding the resistance wire, it has been eliminated. I bypassed it completely when I installed the pertronix kit. The Flamethrower coil, as I understand it, is designed to be used without external resistance. The coil I put on it as a replacement is also designed to be used without external resistance. The points I have on the engine now are just there to see if the engine runs. It does. My dad will not be taking the boat out in its current setup.

We have already ordered a new Ignitor II. I just don't like installing expensive parts like that without knowing what burned up the old one. If it is as simple as replacing the coil and fixing the alternator, then great. That's been done.

 

[chiefalen]

Re: Puzzling problem - Mercruiser straight six

I wish you and your father good luck in regards to fixing this vexing problem.

 

[MikDee]

Re: Puzzling problem - Mercruiser straight six

Your wiring diagram is a bit small for me to read, but the (R) terminal (tan wire) on the solenoid feeds a full 12volts to the coil (positive term) just for cranking. I don't know if you still have this attached or not, or if it even matters to keep it, if you now have a new switched 12v. positive, and no resistor wire anymore?
Not that this is your problem, I'm just making note of it, and wondering if 2- seperate wires feeding 12v. each, to the coil, when cranking does? Now that I'm thinking of this, I don't know, if when you crank the engine, and it's getting a full 12v. from the tan wire, Does the ignition circuit (normally, the resistance wire) temporarily go dead while cranking, till the engine starts (ignition)? so as not to feed too much voltage to the coil at once? It's beyond my elect. tech savvy? But something I'd like to know? this REALLY maybe your whole problem?

Anyway, Where did you get the 12v. switched source from for ignition, if you don't mind my asking? Again, this might be why you're getting a spark from the red wire when attaching it to the Alternator?

Also, it looks like the red wire from the alternator goes thru the Amp guage, and back to the large terminal on the starter solenoid, when the igniton switch is activated, that's what I believe charges the battery, and completes the circuit, (in a roundabout way as I said,,, lol)

 

[Fishermark]

Re: Puzzling problem - Mercruiser straight six

Your wiring diagram is a bit small for me to read, but the (R) terminal (tan wire) on the solenoid feeds a full 12volts to the coil (positive term) just for cranking. I don't know if you still have this attached or not, or if it even matters to keep it, if you now have a new switched 12v. positive, and no resistor wire anymore?

I do still have it attached, but to be honest, I don't know if it is needed or not. I am confident that even if not needed, it isn't a problem.

Anyway, Where did you get the 12v. switched source from for ignition, if you don't mind my asking?

I spliced into the wiring harness right after the main engine harness plug - before the resistor wire.

Also, it looks like the red wire from the alternator goes thru the Amp guage, and back to the large terminal on the starter solenoid, when the igniton switch is activated, that's what I believe charges the battery, and completes the circuit, (in a roundabout way as I said,,, lol)

Yes, it does take the long way around. But the ignition switch does not come into play. The red wire from the main lug on the starter goes through the engine harness to the main connector - then through the boat harness and to the ammeter. Then from the other side of the ammeter back through the entire boat harness - main connector - engine harness to the back of the alternator. Quite a trip! I was going to eliminate the ammeter when I rebuilt the engine but it worked fine and the wiring harness was pristine so I left it alone.

 

[MikDee]

Re: Puzzling problem - Mercruiser straight six

I do still have it attached, but to be honest, I don't know if it is needed or not. I am confident that even if not needed, it isn't a problem.
I spliced into the wiring harness right after the main engine harness plug - before the resistor wire.

The perfect spot!

Yes, it does take the long way around. But the ignition switch does not come into play. The red wire from the main lug on the starter goes through the engine harness to the main connector - then through the boat harness and to the ammeter. Then from the other side of the ammeter back through the entire boat harness - main connector - engine harness to the back of the alternator. Quite a trip! I was going to eliminate the ammeter when I rebuilt the engine but it worked fine and the wiring harness was pristine so I left it alone.

I see all that in the diagram, but I meant, Doesn't the ignition switch turn this circuit on? energize it? I doubt it's live without it being turned on? That's what it looks like in the diagram anyway.

 

[Fishermark]

Re: Puzzling problem - Mercruiser straight six

PROBLEM SOLVED....

Alright. I called my dad to have him do a couple more tests and in the course of doing these tests he discovered.......

Silly question now, Is the battery hooked up right, the right polarity? it's not backwards is it?

Yep - embarrassed to say it - MikDee you hit it early on. He had connected the battery cables backwards when he reinstalled the cables. :redface:

I didn't double check them as the battery was back in its box and I assumed it was correct. (That's what usually gets us in trouble isn't it? assuming?)

The bizarre thing is that the engine started after changing coils - and even ran well. THIS IS WITH THE BATTERY HOOKED UP BACKWARDS. Now granted, that is without the alternator attached.... It is beyond my understanding of things electrical as to how the engine started and ran. It even begs the question of wouldn't the starter spin backwards with the polarity reversed.

Oh well. Thanks again. I'm glad it is solved. I just have a little egg on my face for not double checking the basics.

 

[achris]

Re: Puzzling problem - Mercruiser straight six

From your diagram the alternator output wire is always hot, through the ammeter. This is the way it should be. Alternators, by virtue of design, are reverse blocking. The output is through diodes and should not drain the battery when the engine isn't running. The spark when re-attaching the wire indicates one of the positive diodes (at least) is shorted. Also be design, the diodes should be of a higher current handling capability than the alternator is designed to produce.

So, did the ignition system kill the alternator or did the alternator kill the ignition? My bet.... The alternator killed the ignition. As the diode(s) failed the output would have been spiking. I believe that probably killed the ignition. I would also very thoroughly check the ground cables anyway.

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

 

[MikDee]

Re: Puzzling problem - Mercruiser straight six

Mark, Well I can't say I haven't don't something like that myself over the yrs :redface:

Yes, I'm confused, why didn't the starter spin backwards, and whine while not engaging the gear

But I'm so glad you found out the problem!
Now you just have to repair the collateral damage
By the way, I musta missed your orig. thread, you did a Superb job on rebuilding that engine! I had one I rebuilt myself many yrs ago, and Speed Pro parts matched what I had?! It is one of my fav boat engines, what was Mercruiser thinking when they dropped it.

And Thanks Achris for the info

 

[chiefalen]

Re: Puzzling problem - Mercruiser straight six

Actually in europe it was common for a pos. grounds on cars, first one i saw was on my uncles brand new jag.

Great you found the problem.