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Old 15-01-2018, 12:09   #16
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Re: Yanmar 20GM20 starts but wont run

Check flexible fuel lines for cracks by flexing them near the couplings. I found the lines on my boat from a lot made in 2002 were cracked in these areas, just from routine use. The lines were clearly marked with all the European and USCG approvals. The fittings in the engine compartment, near the fuel pump were worse, probably because of heat. On the suction side they were leaking air into the fuel. On the return side, dripping fuel into the engine bay.

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Old 15-01-2018, 12:41   #17
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Re: Yanmar 20GM20 starts but wont run

Is it possible that your alternator is kicking in and the load is stalling the engine?
Just a thought.
I have had this happen.

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Old 15-01-2018, 12:55   #18
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Re: Yanmar 20GM20 starts but wont run

Some excellent suggestions and guidance here. Thanks to each and everyone (and any yet to come) for your valuable feedback.

For what it is worth, she behaved a lot like this once before, but has run well for the last few weeks. That occasion was on the homeward delivery run where she did much the same thing - died a few times after starting. Managed to get it sorted that time by holding the starter button down while mate kicked her into gear (to apply some throttle), and as I mentioned, no issue since then until just the other day, when that approach didn't work.

Tank contents looks good, primary filter contents look good, haven't checked the engine filter yet but the output side of it (when cracked open) yielded plenty of fuel when cranked for a second.

I doubt it is a blocked tank breather as it dies too quickly to have built up a vacuum in the tank, but will certainly check.

I think I need to check the high pressure fuel delivery next, by cracking the injector feeds one by one and looking for pressure/flow. Maybe I should first bleed at the injector pump input, given I took that line off to look for flow earlier. There is a small PH screw on the injector pump input banjo, which I suspect is the bleed screw. If this gets her back running, even temporarily, I will go looking for potential air leaks into the fuel line

Will also check the exhaust system - the mixer elbow doesn't look like a potential culprit from the outside - a simple right angle with cooling flow input right adjacent to the head, all very clean externally (I know that doesn't mean a thing, but on my own boat that elbow actually looked like a problem from the outside when it choked up solid internally). The pong-box on the other hand (looks like an old plastic S-box off a Nanni-diesel) looks dirty and old and may well be full of gunk.

I don't think it is an alternator load issue, since the engine will start and run for a second or two even in forward gear, which I suspect applies far more load than an alternator could - good thought tho - cheers

Lots of good ideas to pursue!

Cheers all
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Old 15-01-2018, 14:09   #19
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Re: Yanmar 20GM20 starts but wont run

Check that engine filter. I have this same engine, and that little filter gets ignored because it can be a pain to get it off. A little trick if, and only if, you are having trouble. If you just can't unwind it, get the biggest standard screw driver in your kit, slant the tip into the crenulation on the side, and GENTLY tap the butt of the screwdriver. Yes, this might mar the paint, but that will turn the damn thing.
This filter can clog fast, even with a Racor upstream. And the symptoms of a clogged filter are exactly what you describe. If you haven't checked that little bas!ard, I would do that first thing.
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Old 15-01-2018, 15:18   #20
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Re: Yanmar 20GM20 starts but wont run

Originally Posted by Cheechako View Post
Good point. Does any water come out the exhaust? If so, I doubt it would die in a few seconds from partial clogging though.
Over the 35 or more years that I have dealt with the Yanmar 2GM series engines, a situation where the engine starts, fails to come up to power and then dies is usually a partially blocked exhaust riser for reasons that i stated earlier. Do not be fooled by SOME water coming out the exhaust pipe. The water side is not what is blocked but the exhaust passage above the mixing point. When the engine is shut off after running, water in the lift muffler evaporates and collects there as the engine cools. The pH of that water tends to be on the acidic side. Checking the elbow is among the easiest thing to check depending on engine access. Yanmar uses cast iron for these manifolds, and it is subject to severe corrosion. I have switched to an all stainless manifold and so far after 4 years have not had this problem problem.

If you have a cast iron manifold but have not inspected teh discharge for several years, there is a good chance that it is partially blocked. It can be removed and sandblasted clean at least once. Thereafter, replace it.

If the engine stop lever is accidentally left on, or if the control cable has failed, the engine will simply not start at all.

Clogged fuel filters will generally cause the engine to smoke and not reach full RPMs. But they will almost always allow it to start and at least idle.

The lift pump on the engine would be the next area to examine. This can be checked by opening the bleed on the engine mounted filter and operating the lift pump manual trip several times. If fuel comes out, it's okay.
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Old 15-01-2018, 15:20   #21
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Re: Yanmar 20GM20 starts but wont run

Fuel and air. Diesels are pretty simple that way.make sure there are no line breaks in the fuel line. Bleed it well. I've found adding an inline electric pump between the Racor and lift pump make priming easier. I shut it off once the system is primed. It. Also acts as a standby lift pump if you have a failure.
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Old 16-01-2018, 00:28   #22
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Re: Yanmar 20GM20 starts but wont run

Happened to me with a nanni. It was the fuel circuit. I took a canister with diesel, tied it in the cockpit, took a hose and connected it to the injection pump, took the air out of it and motored to the next harbour.
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Old 16-01-2018, 00:55   #23
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Re: Yanmar 20GM20 starts but wont run

When you bleed the fuel do it all the way including the injectors.
Turn off the raw water intake, you will hydrolock your motor, (not good) and turn on the raw water after it starts.
What's the boat history? New to you?
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
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Old 16-01-2018, 02:39   #24
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Re: Yanmar 20GM20 starts but wont run

Wcapman is right..... those elbows are prone to clogging. On my 3HM35f there were 4 bolts connection it to engine..... easy job to remove. Stick with simple things first.
Good luck
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Old 22-01-2018, 06:41   #25
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Re: Yanmar 20GM20 starts but wont run

As a bit of an aside concerning starter fluids - I used to work for a major piston supplier and our technical liaison engineers would regularly blame the customer for using starter fluids if there were broken or scuffed rings in the offing. We wanted to back this up with some hard evidence so we set about a series of engine start tests measuring the cylinder pressures at the same time. Much to our surprise we found it was impossible to get even normal maximum cylinder pressures with starter fluids. The highest cylinder pressures occur only under full load conditions when the engine is really working hard.

So please spray away as much as needed to help locate the fault with no worry about damaging the engine.

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