Quote:
Originally Posted by Andy G
This one has me stumped, so any advice from those with more knowledge on electrical issues than me would be most appreciated.
The boat has twin FL120's. She is on shore power 24/7 & the batteries (2) are fully charged and operated in parallel for starting. Cranking capacity is good.
Yesterday, the Starboard engine fired up as usual, however the Port engine would only crank very slowly, then give up altogether after a few seconds. The Victron charger/inverter would go into shut down mode, lights dim etc. Obviously a lot of power was been drawn down. A general check showed wiring , connections etc to be OK, a gentle tap of the hammer also had no effect.
Am I right in thinking that the issue is likely to be either the starter or the solenoid? However would a fault in either of the starter or solenoid cause the system to shut down.
Any advice much appreciated.
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If you've already figured out the problem, please post the solution for everyone's benefit. Otherwise....
Over my 50+ years of mechanicing (both professionally and privately), I've learned that Diagnostic Rule #1 is always look for the simplest explanation first! For example, you can spend hours chasing an electrical gremlin only to discover that the problem was a blown fuse. If I encountered this problem, my diagnostic process would be as follows:
The biggest clue here is that the engine does actually crank some but slows down. This means it's not the solenoid- they either work or they dont. Second, starters have a similar trait - a bad starter will usually either not crank or crank hard, but at consistent speed. If the latter occurs, crank it a bit then carefully touch the starter body. If its bad it will be hot.
So, assuming the starter and soley are good, the next suspect is current:
1. We can eliminate a fuse or relay because the starter responds.
2. The batteries are probably good because the other engine cranked properly. To find a weak battery, crank the problem engine then test the voltage immediately or monitor voltage while someone else cranks the engine.
3. This brings us to my primary suspect - the cable connections. To test this, crank the engine again then immediately use a temp gun or carefully touch the cable ends at both the battery and the starter. If one is hot, you've got a bad connection. You can also compare the voltage tested across the battery posts, then across the cable terminals.
4. If you want to skip #3, just remove and clean the cables at both ends (my recommendation). It really doesnt matter which end was the culprit because cable connections regularly degrade and should be cleaned periodically anyway.
5. It these tests dont solve the problem, then you should suspect the starter and, as someone else mentioned, try swapping it with the other engine.
Someone mentioned the possibility of water in the cylinder. This is the least probable cause and you would probably have noticed a miss in the engine. However, if you do try hand-cranking the engine, it will come to a stop if a significant quantity of water is present in a cylinder because water will not compress like the fuel-air mixture does. This condition is called hydrolock and the source of water is most likely a blown head gasket. DO NOT try to turn the engine further as doing so can force water past (and even damage) your piston rings. Remove the injectors and crank the engine to determine which cylinder has water.
Good luck