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Old 13 March 2012, 15:11   #11
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if its any help, with the merc/mar/quicksilver anologue tacho when you switch off the obm, say it was running at a thousand rpm the needle will stay at a thousand untill you switch the ign back on then the needle will drop to zero
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Old 19 March 2012, 10:15   #12
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Thanks 9D280 and uncleal. There are no other Merc engines available to compare with.

After poring over the wiring diag and noting the tach signal comes from the regulator/rectifier this was bugging me enough to do the 130 mile round trip to take another look at it. I had that nagging doubt I was going to find a charging problem if I could run it in the shed.

Here's the actual tacho and the needle looks like this ignition off and on. It did give a tiny shiver to the needle on ignition on/off hinting the tacho may not be dead. Three buckets and a hose followed by a lot of mopping but got it running in the shed.

First attempt to turn it over suggested a low battery and then it wouldn't spin. Ominous sign of a dud battery or one that hadn't been getting charged when the engine was running. Jumped it with a fresh battery and metered no voltage rise with the engine revs. With the booster attached it just sat at 12.6, without the booster battery 11.6. In both cases same as battery voltage with ignition off.


Further inspection found the battery positive lug crimp defective - the wire simply pulled out of the lug. I reckon the positive could easily have disconnected the battery with the engine running. In my experience that's instant death for the reg/rectifier and worst case also the lighting coil side of the Stator.

Forgot to meter for AC on the sense wire but was fading fast due to exhaust fumes and pretty sure I wouldn't find any signal.

Next step is to test the reg/rectifier and the stator but pretty sure I'll be at least ordering Mercury 892115-001 or equivalent.
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Old 19 March 2012, 10:21   #13
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team tip Mercury/Marina products never use any p/n that you see on a componant because nine times out of ten that is just a production p/n sometimes they are the same, not very often though always use the OBM serial number to be on the safe side
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Old 01 April 2012, 22:20   #14
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Country: Ireland
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Boat name: Excalibur
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Latest on this I had a Mercury expert come run the proper diagnostics. The stator AC section is shorted to ground. He could test that statically but will need a good stator to test the rectifier/regulator but reckons it's likely gone too. Stator on the way so this rev counter issue is going to be a very expensive fix.

Interestingly he did find what probably caused the carnage - the postive battery terminal crimp had never crimped the conductor and the heavy cable could just pop clean out. It's certain death for the charging electronics of any modern engine in any vehicle if the battery disconnects while the engine is running.

It all took him about 15minutes so good value there except for a few hours travel time

Another interesting nugget/question. The engine had recently had a full service and checkover by a main dealer. IMHO he really should have spotted a basic issue like a poor battery connection. Thoughts?

So two lessons for us here:
1) when routinely checking battery terminals for security,corrosion etc, loss of contact can be very, very expensive and way beyond a failure to start at the quayside.

2) a dead tachometer on at least a Mercury/Mariner is a a real danger sign that you may not be charging your battery and may be unable to key start your engine after shutting down or accidentally kill-cording it

That said, many of us have fishfinders or GPSs at least some of which allow you set minimum voltage alarms. You should set them!
Also as a last resort many outboards have a manual pull-cord start facility. Make sure you know your's and have the cord and the tools to get at the flywheel.
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Old 01 April 2012, 22:28   #15
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So should a dealer service have picked this up?

Here's a picture of the offending terminal showing how the crimped cable had never been sound. When visually inspected it looked fine but a simple tug on the cable revealed the likely culprit for what will be a hefty repair bill.

The fact the red ancillary power leads shown to the left of the heavy lug ran direct from the battery clamp to the lights/instruments/radio etc meant there would be no indication when the engine was running that the engine battery feed had disconnected briefly/partially/etc.
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