Melted wires, anything else to replace?--UPDATE

[nola mike]

So I've been chasing electrical gremlins for a bit, lately limited to a sometimes erratic tach. Driving yesterday, lost power, boat shut down. Started up, ran for a minute, shut down. Tried to restart, saw smoke from back of engine. But it restarted, seemed to idle fine for maybe 5 min, then shut down again when I put it in gear/gave it some gas. One more attempted restart, more smoke, went back in. Found a crispy looking resistance wire that measured 1.9 ohms--a week or so before it was within spec (I had tested it because it felt awfully hot). I was now getting 2-3v at the coil with ign on. Also, the purple/yellow wire from the solonoid-->coil was melted completely through in one spot. Obviously, at this point it would no longer start. Ran out of time to troubleshoot, but I'd really like to get this running again by next week, since I'll have some vaca time an guests in town. So, aside from the resistor wire and the purple/yellow, what else should I replace that could have caused this? Could it be related to the tach? Or a bad coil? Could a bad slave solenoid cause excessive current draw through that wire? I want to make sure I have all possible parts on hand when I do this. I'd rather pay a couple of extra bucks for unneeded parts then be boatless for a week because I can't get something...

 

[Eric 3.7LX Alpha 1]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

I don't think you can get a new resistance wire for the coil. Might have to switch to a ballast resistor to provide the resistance.

I believe the purple/yellow wire powers the coil off the solenoid with full 12v during cranking and then when the key is released the coil is powered thru the resistance wire.

There should be no voltage on the purple/yellow wire while running except what might be coming thru from the resistance wire.

Must have been some kind of short in there somewhere to cause the wire to heat and burn. Maybe from the tach? or solenoid? Maybe a worn spot somewhere on the wire itself that touched ground.
Not sure never had that happen to mine.
Good luck with finding it,
Eric

 

[Don S]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The resistor wire kits are still available.
Merc PN is 84-94227A2

 

[Eric 3.7LX Alpha 1]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

Thanks for the info Don.

I was told earlier this year by my local Mercruiser dealer counter guy that I would have to get the whole engine harness to replace the wire.

 

[stonyloam]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

If only those two wires (to the coil) were getting hot, would seem to indicate a short in the coil. The resistance wire is not part of the wiring harness #31 here: http://www.mercruiserparts.com/Show...nbr=10&bdesc=STARTER+MOTOR+AND+WIRING+HARNESS

 

[nola mike]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

If only those two wires (to the coil) were getting hot, would seem to indicate a short in the coil. The resistance wire is not part of the wiring harness #31 here: http://www.mercruiserparts.com/Show...nbr=10&bdesc=STARTER+MOTOR+AND+WIRING+HARNESS

that was my thought--i'm getting 1.8 ohms between the 2 coil terminals as well, but i don't really know of a good way to test the coil. I was thinking that I may have a coil problem anyway, since i had those erratic tach readings (confirmed with my external meter hooked to the coil). Aside from a physically shorted wire (otherwise the harness looks pretty good) and the coil, the only other thing was if the solenoid was stuck open (closed?), causing the coil to get 12v all the time through the purple/yellow wire. although the resistor wire gets 12v all the time without a problem usually, and i wouldn't expect a constant 12v to harm the pur/yell wire...
so it would probably be easier to just get a coil with a built in resistor and do away with the wire.

 

[stonyloam]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

so it would probably be easier to just get a coil with a built in resistor and do away with the wire.

The problem there is that to get full battery voltage during starting you need to bypass the resistor. Using a internal resistance coil, might make starting more difficult. I would stick with the resistance wire, and if it still reads 1.8 - 2.0 ohms, give it a coat of liquid tape and use it. Doesn't seem like a stuck solenoid would cause the purple wire to get hot. I would try another coil.

 

[nola mike]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The problem there is that to get full battery voltage during starting you need to bypass the resistor. Using a internal resistance coil, might make starting more difficult. I would stick with the resistance wire, and if it still reads 1.8 - 2.0 ohms, give it a coat of liquid tape and use it. Doesn't seem like a stuck solenoid would cause the purple wire to get hot. I would try another coil.

hmm. well, the resistance wire at 1.8-2 ohms is now allowing too much current through it (or it should, anyway, even though i'm getting LESS voltage at the coil, which doesn't make sense). i definitely don't want to reuse it, as it looks physically damaged AND it's out of spec. As far as the starting, my understanding was that the increased voltage to the coil was more for the sake of the points then the coil itself. i mean, these coils in other applications don't get more than 12v to them, do they? i'm running a pertronix otherwise. i'd sooner get an external resistor + wire if i have a hard time getting the OEM wire. FYI, tons of problems with this boat--none of them related to the 470 so far.

 

[bruceb58]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The reason you bypass the resistor during start is becuase operating the starter is already dropping the voltage way down. You are just compensating for that while during start.

To really test to see if everything is "right" measure the voltage at the coil with the points closed. Should be 7 or 8 volts.

How are you measuring the resistance of the coil primary? Are you disconnecting all wires before you test?

 

[nola mike]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The reason you bypass the resistor during start is becuase operating the starter is already dropping the voltage way down. You are just compensating for that while during start.

ah, that makes sense. so i would definitely want to stay away from the internal resistor. but then which applications would these coils work with?

To really test to see if everything is "right" measure the voltage at the coil with the points closed. Should be 7 or 8 volts.

pertronix ignition, not sure how this would work. but it should be binary, no? i either have voltage (points closed) or not (open). shouldn't have a low value.

How are you measuring the resistance of the coil primary? Are you disconnecting all wires before you test?

yes.

thanks!

 

[stonyloam]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The basic problem is that both of the coil + wires got hot, and they are on different circuits, so somewhere you are going directly to ground from the + terminal. I guess it is possible that you have a short in the choke, and current is flowing back through the resistance wire to there, but then other wires would be getting hot too. You could try removing the purple wire, jumpering from the battery to the coil + and see if that wire gets hot when you try to start. If so, the problem is the coil (I think).

 

[nola mike]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

The basic problem is that both of the coil + wires got hot, and they are on different circuits, so somewhere you are going directly to ground from the + terminal. I guess it is possible that you have a short in the choke, and current is flowing back through the resistance wire to there, but then other wires would be getting hot too. You could try removing the purple wire, jumpering from the battery to the coil + and see if that wire gets hot when you try to start. If so, the problem is the coil (I think).

well, they're on different circuits, but connected at the coil. so if one has too much current, it could bleed to the other circuit. i think. my head hurts now. i'm just going to replace the wires, coil, and distro cap, check the other wires in the harness, and see what happens.

 

[stonyloam]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

well, they're on different circuits, but connected at the coil. so if one has too much current, it could bleed to the other circuit. i think. my head hurts now. i'm just going to replace the wires, coil, and distro cap, check the other wires in the harness, and see what happens.

Except that once the solenoid disengages, that circuit is open, and no current flows that way. A nice tall gin and tonic is the perfect cure for a boat headache. Yeah wires and coil should get that 470 humming again.

 

[nola mike]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

Except that once the solenoid disengages, that circuit is open, and no current flows that way. A nice tall gin and tonic is the perfect cure for a boat headache. Yeah wires and coil should get that 470 humming again.

unless it's stuck closed (open?), and you have current still flowing through the wire even with the key in the 'on' position. that was my concern. and there's a keg of yuengling close to the boat at all times...unless it's actually in the water and running

 

[stonyloam]

Re: Melted wires, anything else to replace?

Re: Melted wires, anything else to replace?

unless it's stuck closed (open?), and you have current still flowing through the wire even with the key in the 'on' position. that was my concern. and there's a keg of yuengling close to the boat at all times...unless it's actually in the water and running

That wire comes directly from the slave solenoid, and if stuck closed, the starter would continue to spin. I believe, the purple wire only supplies voltage to the coil when the ignition is on and starter not spinning, and the slave solenoid only applies voltage to the coil when the starter is spinning. They should be isolated at the ignition switch. A tall cold one is a very close second Rx.

 

[nola mike]

Re: Melted wires, anything else to replace?--UPDATE

Well, turned out to be simpler than i thought. i ended up replacing the coil, because i got a new one (the lesson, as always--the problem is never the coil), and the resistor wire, since the old one was pretty burned up. the real problem was that all my wiring was encased in electrical tape (was that from the factory?), and had rubbed through the insulation on the back of the engine block. A little new wiring, and some split-loom plastic casing to protect it, and i was back in action. so this week:
75 miles total
my first time towing skiers on the boat--my brother in law and i went 15 miles over the last 2 days between the 2 of us, skiing/wakeboarding. no issues at all. the boat had a bit of difficulty getting us out of the water (190# each in a double high wrap slalom), but doable. once up it had no problem keeping us at 33 mph, and felt good even making hard cuts--not bad for a four-banger. and though the final gas total isn't back yet, looks like it's less than 20 gallons. hopefully i'm done with problems for the summer...