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Yanmar fuel injection question

Aug 18, 2018
Tartaan Tartan 30 Cormorant Plymouth
I've been trying to get my 2gm going after letting it sit all winter.
When I turn it over, its sounds like it wants to start, but just can't get there. Kind of like only one cylinder is firing.
I had the injectors tested last summer, and both were good.
So, I am wondering if it could be the injector pump. I've loosened all the bleed screws and even some banjo fittings, one at a time, of course, right up to the injector pump. When I turned the engine over, I could see fuel pulsing out of those fittings before tightening them.
So, next I loosened the fuel lines running to the injectors. When I turned the engine over, I could see fuel pulsing out, but it came out in very small spurts.
Is that normal? One internet diagnostic site suggested that I should see a good, healthy pulsating gush of fuel.
So, next I'm thinking about removing the injector pump and having it tested.
Anyone have any ideas before I go that route?
I'm still new at diesels, so thanks very much for any advice any of you might have.


Mar 23, 2017
Hunter 30 Snug Harbor, Lake Champlain
I don't know your 2GM but in general all diesels have a bleed sequence that needs to be followed. It does not include opening banjo fittings. My first guess is that you have not correctly bled the system.

Nov 6, 2006
Hunter 34 Mandeville Louisiana
Decompression levers fully disengaged?
Valve clearance OK?


Jan 20, 2005
Nauticat 321 pilothouse 32 Erie PA
go onto boatdiesel.com and search for the yanmar board 2 GM20F specs. pull off how to bleed instructions. i had one of these engines for 20 years and it sat all winter in -10 degrees w/ no problems whatsoever at startups in the spring after storage. i'd follow the excellent suggestions above, put your injector system back together, forget hauling the i-m pump off to the shop. get your fuel system properly bled , check your voltage on yr starting battery. note that on the 2 gm s the manual bleed lever takes a long time and requires very firm pressure to operate. if you only depress it 1/2 way you're not really bleeding the system.


Jan 6, 2006
Beneteau 423 Mt. Sinai, NY
I would not immediately assume major issue if the engine was running fine last year. Make sure to bleed properly. And also know that once you loosen and then retighten a banjo fitting, the copper washer may not seal properly and leak...... my experience. Have to replace or heat till red.

Good luck
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May 29, 2018
Canel 25 foot Jonathan Shoigama, japan
Hi Tartan.
Think this one through.
It started.
It was laid up and now it doesn't start.
What has changed?
1, Air has leaked into the fuel system.
2. the fuel is old and contaminated.
3. the battery is run down.
other than that nothing has changed , so deal with the obvious first.
1. bleed system slowly and carefully.
2. if possible decant fuel and start with new stuff.
3. Charge batteries to full capacity.

When I turned the engine over, I could see fuel pulsing out, but it came out in very small spurts.
When the fuel is delivered to the injectors from the fuel pump, the pressure and timing are what count.
In general with a small engine like yours the amount is minimal, so I don't see the small spurts as a problem.
However the fuel must be totally free of air.



Jul 24, 2005
Beneteau 323 Manistee, MI
How old is your fuel?
Did you have stabilizer in the tank?
Fuel pickup in the tank clogged?
Evidence of water in the fuel?
When did you change primary and secondary fuel filters last?
Any nearly invisible perforations in the fuel lines letting air into the system?

I guess I have been pretty fortunate over the 14 years I have owned my boat. It has always been stored outdoors over northern Michigan winters, and never had a problem starting up in the spring (knock on wood). The guys at the yard tell me that my boat is on of the few in the marina that consistently starts on the first try after the spring launch.
Jul 1, 1998
Hunter Legend 35 Poulsbo/Semiahmoo WA
Would really not touch the injector pump.
Other possible places for an air leak problem:

1. The bleed screw on the top of the engine filter. The engine filter top is made of pot metal and by tightening the screw too tight, or with numerous tightenings, the threads can become worn.

2. Engine fuel filter O-Ring could be damaged, not seating properly, or tight enough.

3. Engine fuel filter may be clogged as old fuel could have set up a microbe residence there. Has it been replaced recently?

4. When the engine filter is bled, is there a reasonable quantity of fuel coming out of the bleed screw?
Personally, I do not like the engine filter bleed screw setup and whenever there is a problem that is my go-to suspect. Not sayin’ that is the cause but it’s easy to over crank the bleed screw, but not tightening it enough is also a problem. Can’t remember if the washer under the screw is copper or a nylon/plastic type.

Another tell-tail sign of an air leak is if the engine seems to want to run initially but then not so much, it points to an air leak. Also, if you have a water lift muffler, don't crank the engine too long because water can be sucked back in. Open the vacuum break levers for long cranking or allow time between cranking for the water to flow back out.

Since you’re till new to diesels, then welcome to the club. One thing they’d don’t like is an air leak.
Aug 18, 2018
Tartaan Tartan 30 Cormorant Plymouth
Thank you all, for your comments.
The engine is still not running, but I have made some progress, and it ran briefly for about 40 seconds before quitting and refusing to start again.
To get to that point, I bled the system again, going consecutively through all the bleed screws from the secondary filter to the injectors and could see that fuel was definitely getting to the injectors.
When I turn it over, however, it almost starts, but never can get there.
So, here's what I'm thinking about doing next, but not necessarily in this order:
1. Remove all fuel in tank and filters. The fuel appears to be clean and free of water and bio sludge, but it is from the last few days of the last season. Can you tell from its appearance if it is bad, even though it looks OK and the filters are clean? I did replace both fuel filters before I bled the system.
2. Have the injectors tested.
3. Replace all of the copper washers in the fuel system, assuming that at least one could be failing to seal completely.
4. Wrap some 1/2 inch ACCO galvanized chain around it and use it as a mooring...
Thanks once again for your help. While I'm definitely on a pretty steep learning curve, I have to say, I love diesel engines even if they can be a little finicky.
Oct 22, 2014
CAL 35 Cruiser Portland OR, moored EVERETT WA
You could throw the fuel away. I did not. Just mixed some fresh diesel in with the old and started right up. I use the waste not want not theory.

Glad your enjoying your diesel. Engine. They really are simple engines. Need fuel, air and compression.
You say the fuel appears good. And you know the engine oil is at proper level. So how about the air filter?
Then are you able to turn the engine over with the starter?
Lastly, is the exhaust unrestricted.

That’s all I got.
Jul 1, 1998
Hunter Legend 35 Poulsbo/Semiahmoo WA
Here's one more thing to check: The mixing elbow. If it is significantly clogged it'll impact the running of the engine to the point like the problem you're having. It can be a real pain to rod it or check it but it might be worth it. If the raw water connection at the top of the elbow shows much in the way of buildup it'd almost guarantee the inside of the elbow if crudded up constricting the exhaust flow and impacting operation. Not a fun job checking this though.

And another thing: try to make changes in small steps, not all at once, like changing just a few banjo washers at a time. If you buy new washers, ask the Yanmar tech if there are any non-copper ones, like for the engine fuel filter bleed screw for example.


Mar 23, 2017
Hunter 30 Snug Harbor, Lake Champlain
I like the idea of small changes at a time, but when it comes to the fuel system banjo fittings, I would consider that one system. Change all copper seals in the system at once. Additionally, if there is one leaking, when you pump the system with the manual pump building up pressure, you may see it.

Once you are positive there are no air leaks in the fuel system and it is bled correctly, then I would check the injectors timing.

Let me see if I can upload the shop manual for the Yanmar GM series.... It will take several posts. There are 12 chapters in total.




Mar 23, 2017
Hunter 30 Snug Harbor, Lake Champlain
yeap - this will be slow...Darn, chapter 6 is too big. I'll have to break it in half...