1986 OMC 5.0L coil hot and wiring hot *PROBLEM SOLVED*

[newfiez]

Hey guys,

Issue:
I have a customer complaint that the engine was running for about 15 min, then stalled, and could not restart. I found the ground wire loose on the battery, and corroded green. Re-tightened, and the boat started. Ran it for an hour without stalling. Issue I have now is the coil is getting very hot. I also have the purple/red wire going to the + side of the coil getting very hot. Attached to the same wire is a purple/black wire (going to the + on the coil). The purple/black goes to the R on the starter solenoid. The purple/red goes to the alternator, where it's joined (by a crimp) to two wires coming out of the alternator (red/purple and purple), and 2 wires (each are purple) going back into the harness. (SELOC OMC manual 3404, page 10-61, FIG 150 shows this routing is correct).
I swapped out the coil with a 1.5 ohm flame thrower, and had the same issues. The coil that was originally in the boat measures 1.6 ohms

Tests:
Coil + wires purple/black and purple/red disconnected from coil, there's 2.850 ohms at that connection with key off (and battery off). With key on, there's 40.2 ohms.

Coil + wires purple/black and purple/red disconnected from coil, there's 12.4v at that connection key on.

Coil + wires purple/black and purple/red connected, there's 5v key on.

Coil + wires purple/black and purple/red connected, engine running at idle, there's 8.65v (and the tach is wonky), system volts at battery 15.8v

Coil + wires purple/black and purple/red connected, engine running at 2000 rpm, there's 9.24v, system volts at battery 15v

Solution:

Where do I go from here?? I don't see a ballast resistor installed, and it seems like a factory harness. Any help would be great! I'm guessing the purple/red wire from the coil + to the alternator connection is a resistance wire, and it's gone bad and/or the regulator in the alternator is bad.

Thanks,

Jimmy

 

[jerryjerry05]

The voltage to the coil should be 9v.
​The 12 will burn it up.
Some have a resistor in the coil that breaks it down to 9v.
​It should have markings that tell what it is? Resistor or not.

​The wire to the coil might also be a resistor wire??
You'll need a wiring diagram to figure that out??

 

[alldodge]

The 15 and 15.8V is to high, 14.8V is the max you should see. Have you tried running without the tach connected?

 

[alldodge]

Disconnect the tach and field windings to the ALT and see if the coil still gets hot. The 15+ V is to much, something wrong with the ALT or your meter

 

[bruceb58]

What is your dwell at? Too large a dwell will overheat a coil.

 

[alldodge]

Not seeing what your looking at but from my diagram it does show the wires all spliced together. Most all ALT's have a means of disconnecting the wires. As with most ALTs one lead is switched power and the other is sense. The ALT should need both to work, so removing just one side should keep it from working

 

[alldodge]

With the wires disconnected from the ALT don't see it being the coils issue. Might look at the distributor, does it have points, and if so look at the condenser

 

[alldodge]

In order for things to get hot, more current then normal is being pulled thru it. The + side supplies power, the - side pulls power. Wonder if the pickup is pulling to much current?

 

[bruceb58]

The only way the pickup can sink more power is if it's dwell is off(too high). Even electronic ignitions have a dwell angle. Measure it just like a points ignition.

 

[alldodge]

You have something shorting out and the ALT is trying to keep up. The 15.2V on bat 1 tells me the sense lead telling the ALT what the voltage is, well its not connected somewhere. The ALT is running wild and trying to get the voltage up because it either doesn't see the 15V or it sees it somewhere else which is dropping the voltage.

Not a OMC expert by any means but maybe the sense of the ALT is coming from the coil resistor wire instead of from the battery

 

[bruceb58]

The engine is wired exactly like the diagram on page one. You may be right, I have to disconnect the sense wire at the joint, and run it to the battery or starter wire. The weird thing is, when I switch to batt 2, the voltage output drops to normal on the alternator.

Sounds like your sense line is wired to battery 2 only.

Disconnect the sense line and wire it up to the output of the alternator itself and try it. An easy test to do and many alternators are wired up that way now anyway.

 

[Jammer864]

Good Job Bruce!

 

[newfiez]

The 15 and 15.8V is to high, 14.8V is the max you should see. Have you tried running without the tach connected?

I removed the power from the ignition switch for the whole instrument panel, so no gauges would work, but I didn't remove the tach wire from the - on the coil.
The only time I see less then 14v is when I switch the battery selector to ALL or just BATT 2...where those batters almost dead. I've been performing all these tests on the fully charged BATT 1

 

[newfiez]

The voltage to the coil should be 9v.
​The 12 will burn it up.
Some have a resistor in the coil that breaks it down to 9v.
​It should have markings that tell what it is? Resistor or not.

​The wire to the coil might also be a resistor wire??
You'll need a wiring diagram to figure that out??

The only time I see 12v to the coil is when the wires were disconnected from the + on the coil. I was just showing that with the key selected on, there was a 12v supply going to the coil. Once the coil was connected, there was 9v.
The coil I used for the tests was a Pertronix Flame Thrower, that was labeled 1.5 ohms and tested 1.5 ohms.

 

[newfiez]

Disconnect the tach and field windings to the ALT and see if the coil still gets hot. The 15+ V is to much, something wrong with the ALT or your meter

To disconnect the sense or field wires (labeled 1 and 2), I have to cut the wires in the harness. The way it's wired is the 1 and 2 from the alternator are joined together (by a crimp) to the + wire from the coil. The + wire from the coil is also connected to the R on the starter solenoid. So if I were to follow the wire from the starter R, I would pass through the + on the coil and end up at the joint at the 1 and 2 on the alternator. I'll have to either start the engine with a separate 12v source connected to the + on the coil (with the other wires removed) or cut the alternator wires to remove them from the coil to see if the coil still overheats. I will also disconnect the tach and see what happens

 

[newfiez]

Not seeing what your looking at but from my diagram it does show the wires all spliced together. Most all ALT's have a means of disconnecting the wires. As with most ALTs one lead is switched power and the other is sense. The ALT should need both to work, so removing just one side should keep it from working

That's the same wiring as what I have. The wires are hard wired together, going to a rubber block in the back of the alternator, so there's no way to disconnect unless I cut them. Someone's replaced the alternator before, and used butt splice connections. I will see what I can figure out when I'm back to the boat.
The purple/red wire from the coil + to the splice at the alternator is also very hot

 

[newfiez]

Disconnect the tach and field windings to the ALT and see if the coil still gets hot. The 15+ V is to much, something wrong with the ALT or your meter

I disconnected the tach and alternator wires, with no change to the resistor wire getting hot. The new coil with 1.5ohms resistance is not getting hot during these tests. The only time the coil is getting hot, is if everything's connected, with key on only. The coil will get hot to the touch in a matter of minutes.

All test taken from the +terminal on the coil:
- Red/purple ALT disconnect 5.5v key on, 7.5v idle, 9.5v 3000rpm
- Purple ALT disconnected 5.5v key on, 8.5 idle, 10.5v 3000rpm
- All wires connected from ALT, same results as purple wire above.

Test done at battery +:
Red/purple ALT disconnected, 12.7v key on, 12.7v idle, 12.8v 3000rpm
Purple ALT disconnected, 12.7v key off, 12.7v idle, 14.8 3000 rpm.
All wires at ALT connected, 12.7v key on, 13.6v-14v idle, 15v 3000rpm

Next step I think is to get the alternator looked at and see if the problem is stemming from there. Don't know what else to do right now.

 

[newfiez]

With the wires disconnected from the ALT don't see it being the coils issue. Might look at the distributor, does it have points, and if so look at the condenser

It's a Mallory YLM624AV, Magnetic Brrakerless Ignition

 

[newfiez]

Ok, here's the latest:
Installed a new starting battery (#1 battery), replaced one of the two deep cycle batteries that were dead (#2 battery), installed a brand new 1.5 ohm flamethrower, and a new alternator. I've decided to go fresh with parts I had in stock.

Now, here's some readings:
System volts 15.2 on batt 1 only. Coil + 8.5v. Engine rpm 850.
System volts drops 13.2 on both batteries (or just battery 2). Engine rpm drops to 600, and alternator starts to whine.

System volts 15.5v on batt 1 only. Coil + 9.8v. Engine rpm 1750.
System volts 14.7 on both batteries or just batt 2. Coil + jumps to 10.3v, and engine rpm jumps to 3200 rpm.

I've also noticed that the engine rpm at idle will jump up whenever there's a load applied to the 12v system (i.e. Trim up or down).

 

[newfiez]

Oh, and the coil is really warm but not hot, resistor wire is very hot, and alternator almost burned me!
I forgot to mention that the resistor wire measures 2.5 ohms.