Diesel Engine trouble-shooting

Is the oil pressure gauge electric or mechanical?  A sudden brief drop of pressure on a mechanical gauge is extremely serious and may indicate a blocked oil-way or oil pickup.  OTOH on the far more common electrical gauges, it is far more likely to be due to a loose connection somewhere or other electrical supply problem.

I suspect you may be having alternator issues - e.g. a diode in its rectifier shorted and it briefly presented a very high load to the engine until the regulator cut back the field.

Remove the belt, check the alternator turns freely by hand,  identify the charge indicator light on the panel and turn on the engine 'ignition' keyswitch but don't start the engine. 

Connect a digital voltmeter to the battery terminals.  It should read around 12 to 13V depending on the state of charge.  The charge indicator light should be on steady.

Spin the alternator at around 2400 RPM with a socket and an adaptor chucked in a drill.  You need a high power drill and it will tend to bog down so don't run it for long or you will burn the drill out and DON'T let the socket slip on the nut.   The charge indicator light should go out and stay out as long as the alternator is spinning fast enough. If it flickers rhyhmically, you have a failed diode or burnt up stator coil.  If it stays on, its probably bad brushes or a failed regulator and if it flickers erratically its bad brushes or a burnt up slip ring. 

If its good you should see the battery terminal voltage rise at least half a volt, and if it is well charged it should settle around 14V.   If you have a suitable ammeter you can also check the charging current. (i.e. with a DC clamp on one round the alternator output lead - usually a thick lead on a stud terminal, or round one of the battery leads.  Most cheap clamp on meters don't have DC current ranges)

You can follow similar procedures to check the alternator with the belt in place using the engine itself to spin it, but if I were you, I'd want to know if I had an engine problem or an alternator problem before running the engine again.

In all cases, if the alternator appears to be faulty, unless you are an electrical geek, isolate the battery, remove the alternator and take it to a specialist automotive alternator shop.   If you need to reconnect the battery while the alternator is off, you MUST securely insulate the bare end of the output lead.

If you are a real geek, brush and regulator replacement is fairly simple, or even fitting a replacement diode plate.   I'd leave slip-rings or bearings to the shop . . .

The charge indicator warning light connects between the main switched positive in the engine control panel and the junction of the auxiliary diodes in the alternator that provides the field supply to the internal (or external) regulator.  It usually provides the initial excitation current for the field.

In simple terms, if you trace it down the loom it should go to the alternator or just possibly to an external regulator if you have one.

If it goes to a sensor anywhere on the engine block its either oil pressure, temperature or water temperature, but those are not very likely to fail in a way that makes it flicker and even less likely to have coincidentally failed immediately after the engine has unexpectedly stalled.

Simplest test is pull the multiplug at the back of the alternator (if your alternator has one, if its wires on individual terminals you will have to trace it the hard way) and turn the switch on.  The light should then be out and stay out even if you start the engine.  Don't forget the battery wont be charging . . .

If I were you, I'd hope it *IS* an electrical fault as that is a cheap and easy DIY fix compared to the mechanical possibilities.

If it *IS* a failed alternator, check for loose connections and broken wires that are just hanging in place (tug each one) on the high current cabling between both battery terminals and the engine and also on the alternator output cable and inspect the battery switch carefully, testing its contacts for continuity while thumping the bulkhead next to it to simulate engine vibration as by FAR the commonest cause of alternator diode failure is the output circuit going open circuit, even momentarily under load while the engine is running.  IF there is a wiring problem you need to fix it before installing the repaired alternator.

One more possibility is that the alternator belt is badly worn or the belt tension adjustment has slipped, or some debris dropped into the belt as if the belt rode up onto the pulley edge it could have enough leverage to stall a slow running or idling engine, then drop  back into the pulley groove as the engine stopped. This can leave the belt loose enough for it to slip and cause the warning light to flicker.  However you would normally hear something, probably a thud as the belt tried to jump the groove and a lot of rattling (belt slap) or squealing when you ran the engine again.  It *might* be fairly quiet at low revs. BTDTGTTS

Well... the fuel in the filter cup seemed clear with the exception of half a teaspoon of water.  Which I emptied and replaced the filter.  I was having a hard time bleeding the fuel line though so I took off the fuel filter intake hose.

This is the part I hate...  I tried to syphon fuel from the tank and it turned out to be really difficult to pull the fuel and wouldn't continue the syphon once started.  Hmph.  I then blew as hard as I could and blew some bubbles in the fuel tank.  After that, no problem with the syphon.

I would say that implies the problem was a clogged fuel intake and further makes me think this problem will happen again.  *sigh*

Is there an easy way to clean a fuel tank??  The closest thing I have to an inspection hatch is the fuel filler hole and I can't see much in there, and it is impossible to reach in to clean.  Ideas?

We've been through some rough weather this spring;  In June, we pummelled through 8' waves to get out of Toronto harbour, but the remainder of the summer has been reasonably calm.  Exiting Port Dalhousie, when the problem occurred was very rough - 24 hours of north wind had caused a large swell that was working against the 2-4knot current leaving Port Dalhousie.  It was both choppy and reflecting off the breakwalls of the channel.  I can see how that would have stirred up any yuck in the tank and clocked the intake screen.

It was very evident that something was blocking the fuel intake / tank outlet as I was sucking on the hose quite hard to get any sort of flow.

As for the vent, yes, the thought crossed my mind, but while I was testing the syphon, I had the fuel filler hose removed from the tank as I had tried to peer inside.  That, alone, vented the tank with a 1.5"-ish (maybe 2"?) hole.

I have run the engine now for an hour.  The engine plugged away with no signs of problem.  However, the green charging light is still coming on at lower RPM.  I think I will have to trouble shoot that as a second issue.

We were discussing ways to clean out the tank.  I think it goes beyond just cleaning as I suspect that it may be a little rust in the tank... 35 year old steel tank + marine environment = likely rust, yes?  A friend suggested I swish a magnet to gather up any metallic junk as well. Instead of messing with that, I'm thinking of getting a magnet to put on the outside of the tank after I drain it.  I hope this will capture any loose metal particles that may be slopping around in there in the future.

I like your idea of using the oil sucker to empty the tank.  I'll have to see if I can pick one of those up.

I think it's sufficiently far away from the compass, and we're not talking a giant magnet here.  Just something to keep the metal flakes from floating around.

Speaking of which... I installed my new instruments the other day.  *sigh* The wind sense packs interfere with VHF operation.  The field is so strong that even at the very stern of the boat, my handheld radio is inoperable while the wind instrument is on.  I'll post that in another thread...