spontaneous engine startup

I am trying to understand a rather frightening event on our GB 36 with twin FL 120 engines. I was replacing the starboard starter motor that had failed with a cloud of smoke. Start keys were off as well as the circuit breaker for both engines. Disconnected battery cables, removed the starter and started cleaning up. The port engine spontaneously cranked and started. I closed the fuel cutoff by hand and the starter continued to crank. Turned off the batter switch to stop the starter. Nothing had been touched on the port engine and I was no where near it when it started. Nothing fell into the starter to short circuit it. I have been unable to recreate the event but have been leaving the battery cable disconnected from the starter until it can be explained. I would appreciate any good ideas. If this had happened in the middle of the night the boat probably would have burned up.

Dan

From your post I don't know if everything to Port was turned off when the start occurred. If not, and if you have a starting button up top, check that button for a leak around the rubber cover. Those have been known to short out if they get wet, starting the engine.

spontaneous start

Yes, both keys and circuit breakers were off. I have checked that the engine will not crank without both being on. That really only leaves the starter relay and the starter solenoid . But I cannot figure how either can be energized on their own.

dan

Dan Cahn said:

Yes, both keys and circuit breakers were off. I have checked that the engine will not crank without both being on. That really only leaves the starter relay and the starter solenoid . But I cannot figure how either can be energized on their own.

dan

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Wow, you really have a gremlin there, Dan. And now you've just given all of us with Lehman 120 engines (a lot of us) one more thing to worry about..!

Electrical is mysterious. I'd hire a knowledgeable electrician familiar with boats.

Since you were actively working on the starter system of the other engine at the time, I would suspect some sort of power backfeed causing the other engine to start. It seems much more likely to be related to what you were doing as opposed to being a total coincidence that it happened when it did. I would suggest giving the engine control wiring diagram (if there is one) a real good look over to see if there is any possible backfeed path.

yes, a good point about coincidences . Will look and see if there is a diagram.

Dan

I already heard about spontaneous combustion but never about spontaneous engine start
If your port engine started then your port engine starter was energized (yes sound bloody evident eh?). I would follow the cables from the starter to check for any short cut or any damaged cable sheath. Maybe by disconnecting starboard you moved cables and made a short? Then I would continue all the way to the starter relay and push buttons and keys... and if really you find no evidence of damage or corrosion or anything else then I would suspect someone to have done a bad joke. And finally if you were alone aboard, I would immediately put the boat for sale as you may own a ghost aboard

L.

Where did you disconnect the battery cables? At the battery? I am betting not at the battery. Which did you disconnect positive or negative or both? Sounds like you accidentally energized the port starter solenoid some how. Easy to do with a screwdriver or wrench. Doesn't take but 1/2 half a turn to start a diesel that is in good shape and running well.

Part of the mystery is the time delay. If I disconnected the starter cable and removed them and then the port motor cranked, it would be more obvious that the events were related. But there was 5 minutes while I boxed up the motor and was starting to wash my hands. The battery cables are so heavy and stiff, that they did not move an inch after removal.
The port starter is on the outside of the port engine so no wrenches or tools were ever near it.
Dan

So only one solution... who you gonna call?



L.

Believe me, I have been searching for their number...
Dan

I'd start at the starter and measure voltages working back to the battery. Maybe a bad batt selector switch? How many components between the starter and the batt on the big cable? Stray voltage to the solenoid or solenoid wire?

If all that fails, I know an exorcist in Oxnard.

Easting said:

Sounds like you accidentally energized the port starter solenoid some how. Easy to do with a screwdriver or wrench.

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Yup. Or even some other object that shouldn't be around that area

Jeff F said:

Yup. Or even some other object that shouldn't be around that area

View attachment 66685

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OUCH!! That'll get your attention in a hurry!

FlyWright said:

OUCH!! That'll get your attention in a hurry!

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It did mine, just a few days ago. Sad thing is I did the exact same thing on a car much earlier in my life. But I guess in my case I went watchless in most of the intervening years, so maybe I'm not senile yet.

Somewhere you have a short, maybe caused by the other starter burnout. It's become common for manufacturers to use relays to keep the power flow close to the batteries. With a burnout, the dying item draws power (or ground) thru any source. Not only the cables, but possibly some other part of the wiring and frying a relay, connection, place wires rub. Insulation could be melted off wire in a bundle.
You need to carefully check wiring related to the burnout and spontaneously start. Look for a place bundled wires look burnt or heat damaged. Also if the engines have a small relay used to energize the solenoid starting circuit.
Burnout could have gone thru any helm area wiring, too.
Also carefully look for wiring added on, possible improperly. You might have something with a reversed ground.
.

Rain/spray in ignition key or pushbutton start switches. More common than you think. Know of about five instances personally.

Many folks will wire the Alt output to the batt via the heavy starter wire. .

Could the Alt output have been connected to the wrong terminal?

Best guess without a wiring diagram

Sounds like your battery switches were still on. I think that your battery cable that was connected to the starter that you removed touched the starting circuit wire that you removed energizing it. This does not explain why the other engine cranked but how it received its power to crank. I am sure a wiring diagram would explain this though. When I work on a piece of electrical equipment I usually go on the assumption that there initially is only one problem and not coincidental failures. The one problem may cause many symptoms though. I have found this to be true 95 % of the time. I do not believe it was a coincidence that the other engine started on it's own and that the wires removed energized the starting circuitry.

I've had it happen to me. Once, the port engine started spontaneously and was idling happily at the dock until discovered by a dock neighbor. It turned out to be a shorted ignition switch due to a leaking rubber boot in the tower. Then a month later, I arrived at the boat to find the starboard engine alarm sounding. You guessed it, another shorted switch, although the boot looked fine. I should have replaced both of them the first time.

Beware the previous owner, boat yard "electricians", professional qualified electricians and home brewed electrical work...

Nobody can be trusted.

Wires attached here, there and everywhere...

I've seen an 8V71 diesel started via a poorly placed little 16 gauge wire. Complicated Command Vehicle situation, multiple battery banks, multiple circuits, a pair of generators, split shore power... and one little wire incorrectly run between the two sides... Pull the battery switch, push the start button and vroom!

Start tracing.

EVERY wire needs to be assuredly connected, and protected, where it should be.

RB

Roamer Blue said:

Beware the previous owner, boat yard "electricians", professional qualified electricians and home brewed electrical work...

Nobody can be trusted.

Wires attached here, there and everywhere...

I've seen an 8V71 diesel started via a poorly placed little 16 gauge wire. Complicated Command Vehicle situation, multiple battery banks, multiple circuits, a pair of generators, split shore power... and one little wire incorrectly run between the two sides... Pull the battery switch, push the start button and vroom!

Start tracing.

EVERY wire needs to be assuredly connected, and protected, where it should be.

RB

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I am still tracing wires to figure out what is the purpose of each one of them in the spider net I have aboard. And I am still finding some jewels in the connections, the last one being the negative wire from the alternator, around 2 feet long... and made of 3 short pieces of wire twisted one after the other with some tape: pure engineering!

L.