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Old 07-12-2017, 06:14 PM   #1
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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
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Old 07-12-2017, 06:20 PM   #2
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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.
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Old 07-12-2017, 06:25 PM   #3
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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.

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Old 07-12-2017, 06:36 PM   #4
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Quote:
Originally Posted by Dan Cahn View Post
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
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..!
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Old 07-12-2017, 06:38 PM   #5
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Electrical is mysterious. I'd hire a knowledgeable electrician familiar with boats.
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Old 07-12-2017, 07:03 PM   #6
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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.
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Old 07-12-2017, 07:11 PM   #7
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yes, a good point about coincidences . Will look and see if there is a diagram.

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Old 07-12-2017, 07:12 PM   #8
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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

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Old 07-12-2017, 07:14 PM   #9
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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.
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Old 07-12-2017, 07:51 PM   #10
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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.
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Old 07-12-2017, 08:07 PM   #11
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So only one solution... who you gonna call?



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Old 07-12-2017, 08:08 PM   #12
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Believe me, I have been searching for their number...
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Old 07-12-2017, 08:55 PM   #13
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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.
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Old 07-12-2017, 10:42 PM   #14
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Quote:
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Sounds like you accidentally energized the port starter solenoid some how. Easy to do with a screwdriver or wrench.
Yup. Or even some other object that shouldn't be around that area :-)

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Old 07-12-2017, 10:51 PM   #15
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Yup. Or even some other object that shouldn't be around that area :-)

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OUCH!! That'll get your attention in a hurry!
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Old 07-12-2017, 10:58 PM   #16
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OUCH!! That'll get your attention in a hurry!
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.
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Old 07-12-2017, 11:04 PM   #17
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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.
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Old 07-13-2017, 02:05 AM   #18
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Rain/spray in ignition key or pushbutton start switches. More common than you think. Know of about five instances personally.
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Old 07-13-2017, 05:49 AM   #19
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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?
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Old 07-13-2017, 09:51 AM   #20
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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.
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