Main engine fuse blows... sometimes

rjbathgate · 20 December 2009, 04:19

Seems like I'm posting a lot of 'help' posts on here!! My Rib's not all that bad!!!

Anyway, My Mercury 60Hp 2 Stroke has started blowing the odd fuse -- the main outboard blade fuse (20Amps)...

It's quite tricky to debug as it only happens sometimes... but what I do know is this:

It doesn't blow whilst travelling along, or fiddling with any other electronics (radio etc etc).

It blows somewhere between cutting off the engine and then trying to crank it again -- basically, when you've been for a spin, anchor up, go for a dive and then are ready to head back in, engine won't start and you notice fuse has gone...

So common sense tells me it's blowing when I'm trying to restart the engine (can't see it blowing on shut off...)

But I've never been able to recreate it when I want to test it... the other day it blew twice (we stopped twice), but then on my last trip, it blew after/at our first stop, but never again (2 more stops followed).

I know this is a complete stab in the preverbial dark, but where would you recommend I start looking for culprits? Could it still be related to other electrical items (radio, gps, stereo), or does the evidence point to something enginey?

I've read elsewhere that a shorten solenoid would blow the fuse on start, but I know little more about that than that...! And as mentioned, it's not all the time... just when it fancies a bit of attention...

Thanks heaps in advance

Jizm · 20 December 2009, 08:24

Quote:

Originally Posted by rjbathgate

I've read elsewhere that a shorten solenoid would blow the fuse on start, but I know little more about that than that...!

It's a good place to start, get the meter out and check thhrough the start circuit, have a wiggle on a few cables and check the general state of the wiring. You could eliminate the electronic units by dis-connecting them completely. Just an idea.

9D280 · 21 December 2009, 09:15

When it;s popped, does it show any signs of life before nothing happens? (e.g do you get your warning buzzers / can you hear the remote choke clicking kind of thing?) That would confirm it's not blowing on shutdown. If that all behaves normally, and when you turn the key absolutely nothing happens, that would hint you ainly getting juice to the starter.

I'd suggest the "meter over the solenoid" is probably a good place to start. Another way to test it might be to disconnect the big juice cable from solenoid to stareter (at the solenoid end so you donlt have a live cable waving about) turn the key & see what happens - if it pops the fuse without the starter, then you;ve found the problem.

Might also be wirth going through the remotes with a meter - The witring in there isn't infallable......

Assuming it's PT, and of a certain age, I think your trim solenoids should be the same as the starter one (swap to test it).

rjbathgate · 21 December 2009, 09:47

Quote:

Originally Posted by 9D280

When it;s popped, does it show any signs of life before nothing happens? (e.g do you get your warning buzzers / can you hear the remote choke clicking kind of thing?) That would confirm it's not blowing on shutdown.

No alarms, buzzers or clicks than I can tell... when fuse is gone and i turn key, nothing at all, complete silence... especially on the faces of the people on board ha!!

Borrowing a multimeter tomorrow - will get probing and testing... and try and find the solenoid!!

9D280 · 21 December 2009, 11:09

Maybe I should have been more explicit - next time it happens, don't go straight to "crank" position with the key, set it to "run" & see what happens (i.e can you hear the choke solenoid if you hit the choke kind of thing)

Not all engines buzz on start - I was trying to be overly general. If it normally does, that might hint it's happening on power down.

alystra · 21 December 2009, 14:52

In view of my experience during the summer, I wonder if you have a problem with the regulator/rectifier. Is there a smell of hot insulation near it? The main fuse blew on my engine - not surprising really as the rectifier sprayed a jet of molten metal over the engine block. This wasn't obvious until I unbolted the regulator and looked at the back of it.

Roger Barr · 21 December 2009, 20:16

I had the same thing a few years ago on mariner 150, couldn't get to the bottom of it, had me flumoxed!

Eventually traced it to a bared wire in the for the trim and tilt switch in the control box.

The break in the insulation was down near the pivot point and every now and then it would short out blowing the fuse, when you went into neutral. You wouldn't know until you went to start the engine again as it kept running with the fuse blown, or if you were lucky you'd notice if you tried to adjust the trim.

Worth a try.

Cheers.

rjbathgate · 21 December 2009, 20:27

Quote:

Originally Posted by Roger Barr

trim and tilt switch in the control box.

Silly question, but where would this be?

Cheers

rjbathgate · 22 December 2009, 05:30

Hey

Righty, I have just:

completely cleaned, checked and tightened main battery terminals (although they were pretty good already)

cleaned excess gunk/grease/oil from what cables/connections in engine I can

I have a question... in order to check wire connections by 'wiggling' them all, don't i need the key in crank/start position in order to juice up all the connections to engine? And as such, if I have someone hold the key in crank/ignition, the engine is gonna start, and then constantly be on crank -- isn't that bad for the engine?!

Going out again tomorrow so will see if it happens again... it's just annoying that I haven't found an obvious cause... id just like to know what's causing it arrrgghhhhh!!!!

Cheers

Poly · 22 December 2009, 09:17

Quote:

Originally Posted by rjbathgate

I have a question... in order to check wire connections by 'wiggling' them all, don't i need the key in crank/start position in order to juice up all the connections to engine? And as such, if I have someone hold the key in crank/ignition, the engine is gonna start, and then constantly be on crank -- isn't that bad for the engine?!

You can check for a short with e.g. a multimeter. Only the starter motor cables need the key at 'crank' to be 'energised' the rest should be 'live' with the key at 'run'

9D280 · 22 December 2009, 09:28

I hate my firewall.....just wrote a suggested diagnositic & it dropped the connection along with my essay, so, a summary version:

In answer to your trim / tilt switch, I guess if you are asking that, you don't have power trim? - it's the switch you might have on the side of the end of your remote throttle / gear lever. Some engines have a "local switch on the side of the cowl as well. If you don't have PT, you wonlt have either......

If you taking the fuse out, and it;s intermittent, poking wires will be a long tedious process & preobably never find it. So, suggestion - wire a bulb on the engine side of the fuse. this will stay lit whenever the fuse is not blown. Go for a burn, you wil lthen see when it;s blowing. IF it's the regulator, it'll probably go above a certian RPM or after a few mins at WOT. Most engines (apart form a few new suprr high tec ones) only really need the battery to turn the starter, so the fuse could blow seconds after it fires, and unless you have a something telling you the voltage you'll not know until you next try to start the engine.

Fuses only go when there's too much current. A visual check would be fto scour all wiring, &look for chaffed or bare wires - that should eliminate a short.

rjbathgate · 23 December 2009, 21:53

Tried and tried to blow a fuse yesteday, did it happen...

nope...

ADDITION...

Just found a dodgy connection in my console between battery and gps receiver unit... resulting in gps receiver not responding on the odd occasion... which now works again

completely unrelated to engine expect for it's all on the same main battery....

Wonder if that could cause fuse pop...