Yanmar 3gm30f - Occasionally sputters and dies on start up

[MondayNever]

Hi all,

My Yanmar 3gm30f is acting up. I've only owned the boat for a few months and the diesel ran tip top until very recently. Always started within a second or two of cranking her over and never more than a couple seconds of smoke at start up and then none visible afterwards. In the last couple of weeks some changes have come over her. Symptoms:

- On 4 occasions she has taken 4-5 seconds to start and then has idled really roughly with lots of vibration at low RPMs (500ish) and then died. When I turn her over again she has caught, coughed, and then run smoothly after puffing out a bit of smoke. This has only happened first thing in the morning after at least 12 hours since the last run. She always starts and runs smoothly for the rest of the day.

- She is putting out a bit of white smoke on some occasions. Not a lot, but more than she ever did before. Yesterday it was everywhere from idle to 2500 rpm. Today, hardly a hint of smoke however.

- If I reverse under load, primarily when setting the anchor, she is hard pressed to go over 1500 RPMs and puts out black smoke in the process. When I throttle back down to idle she kicks out a bit of black crap in the cooling water. This is not a new problem, however, and has been the case as long as I've had her. The boat has a 3-blade feathering prop, if perhaps that has any relevance to the difference in reverse versus forward.

One theory about the starting problem:

The batteries are not isolated properly (previous owner) and on occasion I forget to set the selector switch to the right position for starting and then charging. Sometimes I accidently partially drain the engine battery while using house electronics. I a,m guessing the engine batt has suffered due to this. Perhaps if it has been sitting idle overnight and is not in a full state of charge, it's cranking amps are low and cannot spin the diesel quickly enough, hence the 4-5 seconds to start. During that process, unburned fuel is gathering in the cylinder, causing the sputtering when it finally catches. Once the cylinder has been cleared of fuel, she restarts properly. Any merit to this theory?

I don't think it's bad fuel, as we've got brand new filters in place that are clean and I would imagine this problem would continue beyond start up. I haven't checked the air filter yet, though. Is that a possibility?

All ideas are welcome. I'm currently in St. Kitts and will sail to Guadeloupe over the weekend in hopes of finding a Yanmar technician in Pointe a Pitre. I'd rather avoid him if it's something simple though!

Thanks!

[sailorchic34]

Check your banjo bolts between the lift pump and the fuel filter. Seems yanmar used bolts about 1/8" too long and they will loosen over time. A tiny vacuum leak there will cause your symptoms. I tighten mine about every 50-100 hours.

[the_alpine]

I too was going to suggest some sort of small vacuum leak. Likely places: fuel filter lines, bleed screw(s).

[MondayNever]

I'll give them a check in the morning. Thanks!

I'm surprised that a vacuum leak would only manifest at start up, rather than continuously, though.

[captstu]

A vacuum leak is the likely cause. Before starting the engine, operate the mechanical fuel pump level for a few strokes - if there is initially no pressure and it builds after a few strokes, find the leak - it may be in the diaphragm of the pump or the bango bolts, or the fuel filter.

[foxfire]

Almost certainly fuel related. Don't forget to check the small secondary filter on the engine in a metal housing, it's easy to overlook and mine was the cause of similar fuel problems

[Liam Wald]

Be careful tightening the bleeder on the secondary filter as the treads are very easy to strip. I think that the threads are tapped into cast aluminum or some kind of pot metal.

[MondayNever]

Wouldn't start at all this morning, even after tightening banjo bolts and bleed screws. None were loose, but a couple were able to be snugged a quarter turn or so. Decided to start from scratch and replace both filters and bleed system. The racor filter was pretty dingy looking though it was fine when I checked ~20 hours ago. Engine filter looked fine but replaced anyway. Bled the low pressure side and then tried to start. Caught in a couple of seconds, sputtered a bit, then started humming along as normal.

Hard to tell whether this fixed the issue or not. We'll see how she starts up tomorrow. Thanks for the tips!

[hamburking]

Originally Posted by Liam Wald

Be careful tightening the bleeder on the secondary filter as the treads are very easy to strip. I think that the threads are tapped into cast aluminum or some kind of pot metal.

This happened on my 3gm and I had a very small annoying fuel drip forever after.