Short? Or bad component preventing engine from shutting off?

[joe_db]

Easy test:
Start the engine and let it run a bit.
Turn the key off.
If it still runs, remove the wire that goes from the coil to the distributor.
If the engine quits, you still have power going to the coil.
If it still runs, it is dieseling ("running on"). Cars back in the mod 70s would do this. I think it is usually caused by excessive carbon buildup. Something ends up getting hot enough to ignite the fuel/air mixture without a spark.

[ILikeRust]

It's definitely not run-on. I had a 1977 Chevy that did that, and I know what that's like. An engine running-on sputters and shudders and clunks and then finally dies.

I'm confident this is the coil remaining energized, because the engine just continues to run perfectly normally, as if I never switched the switch off at all.

[joe_db]

I have had the key switch go bad in airplanes and refuse to shut the engine off. Since we usually cut the fuel to shut down, this can be quite dangerous because you might not know it happened until someone moves the prop

It's definitely not run-on. I had a 1977 Chevy that did that, and I know what that's like. An engine running-on sputters and shudders and clunks and then finally dies.

I'm confident this is the coil remaining energized, because the engine just continues to run perfectly normally, as if I never switched the switch off at all.

[ILikeRust]

I have had the key switch go bad in airplanes and refuse to shut the engine off. Since we usually cut the fuel to shut down, this can be quite dangerous because you might not know it happened until someone moves the prop

See above - I have already replaced the key switch, to no effect.

[joe_db]

Do you have ANY other connection to the + side of the coil other than one wire direct from key to coil?

See above - I have already replaced the key switch, to no effect.

[ILikeRust]

Do you have ANY other connection to the + side of the coil other than one wire direct from key to coil?

That's what I need to check out, which I plan on doing this weekend. I have not yet taken a good look at what's connected to the coil.

[joe_db]

On my boat there is another wire that goes to the voltage regulator. It turns the field current off when the engine is not running. If my regulator became defective and fed current back down that wire to the coil, the engine would not shut off.

That's what I need to check out, which I plan on doing this weekend. I have not yet taken a good look at what's connected to the coil.

[JOHN COOKSON]

Engine Won't Quit - Part Two

If the problem is wiring related and you have a wiring harness or plugs in the circuit between the key and the coil pull them apart and check for moisture or water that might be causing a short in the plug(s).

If there is a boat wiring problem you should be able to get normal operation by running a bypass wire from the key to the coil. This should be diagnostic.

YOU SHOULD HAVE THE BATTERY DISCONNECTED OR THE CIRCUIT BREAKER OFF AT ALL TIMES EXCEPT WHEN YOU ARE WORKING ON THE BOAT AND GET THIS PROBLEM SOLVED. IF YOU DO HAVE A SHORT AND THE SHORT SEES GROUND YOU WILL HAVE A DISASTER.

TRUE GRIT

[ILikeRust]

Well it seems - for now, at least - that I "fixed" it.

I started tracing wires from the coil to see what went where and ended up sticking my head behind various bulkheads and spaces and finding miles of wire. The boat is 42 years old and I am at least the fourth, if not fifth, owner. Considering how simple and spartan the boat is, I'm suprised how much wiring there is all over the damn place.

Anyhow, while carefully investigating the wiring all around the engine, I discovered that one of the spade lugs on a wire connected to the electric fuel pump seemed to very, very close to , if not touching, a metal fitting. That wire provides power to the electric fuel pump by coming off the coil. So I thought maybe I was getting a short there. I gently bent the spade lug to move it away from the fitting. There was no sign of arcing or anything, though, so I really don't know if that was the case.

I also found a couple terminals that were just slightly loose, so I snugged them up.

I then found wire with a spade lug on the end hanging free, near the alternator. So now I'm thinking, oh great - was this supposed to be connected to something and it came off? Or is it just an old wire that someone disconnected but never pulled out. Well it turned to be an abandoned circuit that never was pulled out. I think it was for powering an old radio or Loran or something. Anyhow, the fun part is that it was one wire of a three-wire cable. The other two wires were STILL CONNECTED to the batteries! The other end of the cable was just cut off and lying on a shelf. I of course disconnected and pulled them all out.

I think it might - might - have been possible that that abandoned circuit was causing an intermittent short.

Anyhow, when I tried the key, it worked perfectly. Yesterday I took the boat out with some friends, and at the end of the day, when we motored back in to the dock, I turned the key and the engine shut off as it's supposed to.

So - either one of the things I did actually fixed the problem, or just the fact that I dug around in there and wiggled various wires all over the engine might have done it.

The question is whether it will start doing it again. Which I will have to see.

Next up: replace the leaking head gasket!