Yanmar 2QM15 starts hard

[Mike8221]

Engine turns over nicely and has spark, but acts like it may be getting too much fuel. Some black soot/oil coming from exhaust but only at startup. I use about 75-80 pct throttle when starting. I have also experimented with less throttle with no improved results. Last year i had injectors rebuilt. New fuel /air filters. This year i cleaned the ground wire connection which helped a lot. Is it possible i may still have a weak ground connection?
I hate to leave an oil slick evertime i startup!

 

[bria46]

Diesel engines don't use spark plugs they use glow plugs!

 

[haggler]

2qm15

Diesel engines don't use spark plugs they use glow plugs!

And the 2QM15 doesn't have those either.

 

[Barnacle Bill]

Black smoke is the most common smoke emitted from diesel engines. It indicates poor and incomplete combustion of the diesel fuel. There are many causes, including…
Incorrect timing
Dirty or worn injectors
Over-fuelling
Faulty turbocharger (ie not enough air to match the fuel)
Incorrect valve clearance
Incorrect air/fuel ratio
Low cylinder compression (eg sticking piston rings or worn components)
Dirty air cleaner
Restricted induction system (eg system too small or kinked inlet piping)
Other engine tune factors
Poor quality fuel
Excessive carbon build up in combustion and exhaust spaces
Cool operating temperatures

 

[Mike8221]

Startup is easier with 90-100pct throttle. From there it is struggling for 30-45 seconds and then revs up and runs with no problem. I am beginning to think the mixing elbow is the real culprit. My next project. Suggestions?

 

[Bill Roosa]

mixing elbows and intake systems are not the problem if it runs OK at speed. The draw of the intake and amount of gas that goes out the exhaust at cranking speed is MUCH LESS than when running.
You say it runs badly for 30-45 seconds after starting then runs fine and you get black soot and oil during that time out the exhaust. I'm thinking some of the injectors are not misting the fuel well and the cylinders have to get heated up to get the fuel to burn
or
you have a sticking valve(s).
Does the engine start well when it is hot?
Does it start well after it has been run recently (day before) but is not warmed up?

 

[Mike8221]

mixing elbows and intake systems are not the problem if it runs OK at speed. The draw of the intake and amount of gas that goes out the exhaust at cranking speed is MUCH LESS than when running.
You say it runs badly for 30-45 seconds after starting then runs fine and you get black soot and oil during that time out the exhaust. I'm thinking some of the injectors are not misting the fuel well and the cylinders have to get heated up to get the fuel to burn
or
you have a sticking valve(s).
Does the engine start well when it is hot?
Does it start well after it has been run recently (day before) but is not warmed up?

The injectors were rebuilt last summer after having the same problem. It starts ok when hot. the soot/oil was much less on start-up the last 2 times from a cold start.
It is only started a handful of times each week. I live 2 hrs away. Are you suggesting some kind of fuel additive/cleaner ? Recommendation is appreciated.

 

[heritage]

Don't forget to check for an air leak around the fuel lift pump and the secondary fuel filter. There are several banjo connections with copper washers that you should check for leaks and carefully tighten if necessary. The bleed screw on top of the lift pump has a gasket that is prone to leaking. The filter may not be seated firmly. If air is leaking into the fuel line, after a few days there will be enough in the fuel line to cause slow starting. When it finally does start, the unburned fuel is spit out the back as oil and black smoke.

 

[Mike8221]

Don't forget to check for an air leak around the fuel lift pump and the secondary fuel filter. There are several banjo connections with copper washers that you should check for leaks and carefully tighten if necessary. The bleed screw on top of the lift pump has a gasket that is prone to leaking. The filter may not be seated firmly. If air is leaking into the fuel line, after a few days there will be enough in the fuel line to cause slow starting. When it finally does start, the unburned fuel is spit out the back as oil and black smoke.

I appreciate your suggestion. How do i check for an air leak?

 

[Mike8221]

Don't forget to check for an air leak around the fuel lift pump and the secondary fuel filter. There are several banjo connections with copper washers that you should check for leaks and carefully tighten if necessary. The bleed screw on top of the lift pump has a gasket that is prone to leaking. The filter may not be seated firmly. If air is leaking into the fuel line, after a few days there will be enough in the fuel line to cause slow starting. When it finally does start, the unburned fuel is spit out the back as oil and black smoke.

After a little thought it occurred to me the only way to check for an air leak will be to check each time i go back for a couple of times and actually bleed the system. Such is life, but at least i will know. Thanks again.

 

[David W]

Engine turns over nicely and has spark, but acts like it may be getting too much fuel. Some black soot/oil coming from exhaust but only at startup. I use about 75-80 pct throttle when starting. I have also experimented with less throttle with no improved results. Last year i had injectors rebuilt. New fuel /air filters. This year i cleaned the ground wire connection which helped a lot. Is it possible i may still have a weak ground connection?
I hate to leave an oil slick evertime i startup!

Hi Mike. I also have a 2QM15 from 1978. A couple of questions: does the starter crank the engine well? It will take a few seconds before there is enough heat built up to fire. Mine will crank for about 10-15 sec before it starts to fire, during that time fuel is being injected so when it does catch the exhaust is definitely black.

After clearing the initial fuel, I let it warm up at about 1000 or so rpm. There is no smoke at this point. I do get some white smoke when it's warmed up and underway but I know the compression is low-ish so there is unburned fuel in the exhaust.

We have a glow plug fitted but when I start the engine without it I get pretty much exactly the same result as you. When I use the glow plug, I energize the plug for 20 sec or so then crank with about 1/3 throttle and she fires almost immediately. The glow plug is essentially creating a hot environment for the atomized diesel, same thing that occurs after the engine cranks and builds heat through compression.

These older engines will never operate the same as their newer counterparts, so I just take comfort in the fact that she's 34 years old and will still cruise all day at 2200 rpm.

 

[Mike8221]

Hi Mike. I also have a 2QM15 from 1978. A couple of questions: does the starter crank the engine well? It will take a few seconds before there is enough heat built up to fire. Mine will crank for about 10-15 sec before it starts to fire, during that time fuel is being injected so when it does catch the exhaust is definitely black.

After clearing the initial fuel, I let it warm up at about 1000 or so rpm. There is no smoke at this point. I do get some white smoke when it's warmed up and underway but I know the compression is low-ish so there is unburned fuel in the exhaust.

We have a glow plug fitted but when I start the engine without it I get pretty much exactly the same result as you. When I use the glow plug, I energize the plug for 20 sec or so then crank with about 1/3 throttle and she fires almost immediately. The glow plug is essentially creating a hot environment for the atomized diesel, same thing that occurs after the engine cranks and builds heat through compression.

These older engines will never operate the same as their newer counterparts, so I just take comfort in the fact that she's 34 years old and will still cruise all day at 2200 rpm.

Where can i get more info on fitting a glow plug? I didn't think it was possible to install one on these older engines. I just bought a 1985 Kuboto diesel tractor with a 25hp engine that has a glow plug. When I use the glow plug it starts up after about 5 cranks every time.

 

[kloudie1]

Mike, these things are made to cold start Yanmar tractors that have the same engine .. It fits in that big boss in your intake manifold.. Might be what David is referencing.. Not a conventional glow plug..
http://www.hoyetractor.com/thermostart.htm
Ya need to verify if it actually fits in your engine..

 

[David W]

I actually don't know as the glow plug was in place when we bought the boat. I can take some pics if you're curious about the finished product. It's a prettily simple affair all told.

 

[David W]

Mike, these things are made to cold start Yanmar tractors that have the same engine .. It fits in that big boss in your intake manifold.. Might be what David is referencing..
http://www.hoyetractor.com/thermostart.htm
Ya need to verify if it actually fits in your engine..

I haven't seen the business end of the glow plug, but the top bits match what I have. Cool site find. Appreciate the reference!

 

[Mike8221]

I actually don't know as the glow plug was in place when we bought the boat. I can take some pics if you're curious about the finished product. It's a prettily simple affair all told.

David, pictures would be great. Thank you.

 

[Stu Jackson]

Consider KISS and maybe no problem. You most likely have a water lift-type muffler. If so, while you're away those mixed engine exhaust gases and cooling water are sitting in your muffler for two weeks. Even if you were on your boat daily, they'd be sitting overnight. You will always get some oily discharge from a muffler exhaust. Where'd you think it was coming from?

You maybe don't have any problems at all.

 

[Mike8221]

Consider KISS and maybe no problem. You most likely have a water lift-type muffler. If so, while you're away those mixed engine exhaust gases and cooling water are sitting in your muffler for two weeks. Even if you were on your boat daily, they'd be sitting overnight. You will always get some oily discharge from a muffler exhaust. Where'd you think it was coming from?

You maybe don't have any problems at all.

As should be obvious by now i am not a mechanic. Different opinions from different posts raise different questions.

I have no idea where it is coming from. That still doesnt answer my starting "question".

 

[Stu Jackson]

Mike, sorry, but that was my point. The "soot in the exhaust water" is coming from the muffler. I'm no mechanic either (but I've learned how my engine and its parts work), so the exhaust gases mix with the water injection right before and inside the muffler. All that "dirty" water is sitting there, waiting to get expelled. That's all I was trying to say. You don't have trouble starting the engine, you just notice the crud when it does start, right?

 

[Rob2435]

I have a 3GM30F and never put the throttle up to start the engine. It starts quickly, after a few cranks, maybe 3. Throwing the throttle up to 90% would inject fuel into the engine and it would be nearly impossible to burn it all when starting as the first couple of cranks don't burn everything. I would start the engine on idle and see how that goes...It's worked fine for me on all the different boats that I have sailed.