electrical mystery

[Bobg]

was motoring along one day, I plugged a usb plug into my cigarette lighter receptacle, noticed a spark at the receptacle, and the engine stumbled, tried it 2 more times, when the spark would show, the engine stumbled.  after reading the post on low oil alarm, Ron mentioned engine fuel lift pump, do you think this was shorting out that?  I wasn't aware that it had a electrical connection, not at the boat now, going up today.  Not a problem, as the usb plug was defective to initiate the spark, and I threw it away.   the receptacles are fused, but before fuse blew, the engine momentarily stumbled.  got us all confused on the dock.  The stumble was immediate, i.e. spark, equals instant engine stumble.  So if there is a short in the dc side of the boat, the engine quits?  Everything is fine now but, Any ideas would be nice to hear, and yes, I should change the name of my boat  :)  Thanks guys, Bob

[mark_53]

So if there is a short in the dc side of the boat, the engine quits?

The engine should not quit. A fuse should have blown.  You may look at downsizing the fuse off the receptacle if it did not.  When the USB shorted, it would have caused a spike in the current draw from the alternator which would cause a noticeable "stumble" from the engine.

[Bobg]

I have a 30 amp in line fuse..which did eventually blow..ill take your advice and downsize to 15..so the stumbling is from the alternator momentarily pulling hard on the engine...kind of what some of us thought. But nice to get verification from this trusted forum.thanks Mark

[Footloose]

Bob,

If the USB shorted you have that problem figured out.  If it was the receptacle arcing that is a different problem.  Arcing does not cause overcurrent and will not blow the fuse.  However, arcing does cause fires.  If it is arcing, replace the receptacle.

[Ron Hill]

Guys : The oil pressure and the lift pump correlation is only for the M35 series and M25 XPB engines. 
For the M25 & M25XP engines the oil pressure and lift pump operate independently!!

A thought