B5.9 M-270 Electrical Issues

[Stan Johnson]

Good Morning,

I have an interesting problem that popped up on my starboard 6BT 270 last week (eng. serial number 45841642). While cruising at 1500 RPM’s all of a sudden my tach gauge started fluctuating back and forth between 1500 and 1800 RPM’s although the actual engine RPM’s didn’t change. At the same time I received a flickering low oil pressure light and flickering low voltage light for that engine. The engine was immediately pulled back to idle to let it cool down for shut down. After shutting the engine down I continued on to an anchorage on my port engine.
Once anchored I opened the engine hatch I checked the engine oil and gave a quick look for signs of trouble and after seeing nothing obvious, attempted to start the engine again. After attempting to crank a few revolutions I looked back to the engine hatch and noticed smoke coming out. Investigation revealed that my fuel shutoff solenoid was completely fried. It looks like the solenoid shorted internally and then completely burned through the insulation on two of the three wires. I then cut and capped the 3 wires on the engine harness side (feeding the solenoid), and removed the solenoid. I then manually opened the fuel shutoff lever, started the engine and proceeded to pull anchor. About 1 minute in to pulling the anchor I hear a noise coming from that engine that sounded like the VHF squelch was turned down to low. I went back to check and found that my engine starter had decided to engage well after the engine was already running. After shutting the engine down investigation revealed that in order to use the engine I had to start the engine and then turn the key switch off which allowed the engine to run but without any engine instrumentation. If I run the engine with the key switch on after starting then I get the flickering low oil pressure, low voltage warning lights as well as intermittent starter engagement while the engine is running. Other than the obvious replacement of the shutoff solenoid and probably the starter magnetic switch, does anyone have any ideas on what else might have failed to cause this problem? I don’t see any interconnection between the starter and the fuel shutoff solenoid other than sharing space in the engine harness.

Thanks

Stan

Topic

[Stan Johnson]

Follow Up

Thank you for the advice gentlemen. As it turns out, in addition to the fuel shutoff solenoid shorting out, the mag relay directly forward of the starter mag relay fried as well. A guy that ties up next to me had spares of both he gave me and after installation (including Tony’s FSS ground advice), everything works fine.

[Corey Schmidt]

Connections

Sounds like it’s a good time to assess ALL electrical connections to make sure that everything is TIGHT, CLEAN, and RUST FREE…

Start at the battery, then the engine, than all the way up to the instruments and key, etc.

[Rob Schepis]

Sounds like a ground may have gone bad or went fully open?

The “interconnection” between the starter and the fuel solenoid is that the solenoid “pull-in” coil is energized by starter during cranking.

[Author]

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