I have a Mustang 930 with 3 cyl Yanmar 3TN82 motor. It is very hard starting in any temp. Air preheat works but does not help the running or starting issue. Starts on one cyl and runs like a hit and miss motor for up to 2 min. Then it just clears up and runs and takes throttle normally. Leave it sit for 10 min and it stumbles a bit on startup. It has black smoke on startup when it is running rough; that clears right up once it runs normally. Takes throttle nicely and no smoke or stumbles when it has run 2 min. I have not checked compression. Only has 1900 hrs and seems to have lots of power otherwise. There is some fuel seepage at the fuel shutoff valve on the fuel filter cartridge housing. Not certain if it is introducing air in the lines there? When it is running rough on startup, it will like be a switch that all of a sudden it will start running normally. Any other ideas on the hard starting on how all of a sudden it clears out and runs fine. I have not changed the fuel to newer fuel; maybe 2yrs old, but it seems to runs fine otherwise when warm. I have not checked valve clearances or checked pump timing. I doubt that those would cause this issue. Any other ideas of air may get into the lines or system? Does it seem like I am on the right track? Thanks in advance for any advice/
Fuel could be draining back due to a bad check valve, or that leak you described
Check valve would be located where where
Injector pump or filter housing, I've never had to find one on a Yanmar, sorry.
Sounds like an air leak. So when you shut down, your fuel line sucks in some air (probably at that spot that you noted). The air then purges when you start it up - runs great when all the air is out. I would replace all your rubber lines and double clamp. See if that helps.
I have replaced the fuel hoses coming out of the tank, going to the fuel filter housing, to the injection pump and to the fuel pump and put on new clamps and tightened securely. I replaced the O rings in the filter housing and even siliconed the outside of the shutoff valve close. The problem is still there. I was going to check the top of the filter housing for an air bleed fitting. Also going to replace the outlet hose out of the fuel pump with a clear hose, so I could see if there were any air bubbles. Was also going to try and set up an external fuel tank supply and go directly to the fuel pump and bypass the filter housing. The stock fuel tank is totally over the engine and it feeds out the bottom of the tank; so that rules out an issue with the pickup tube. The tank is also full of fuel. If I try and restart within 2 min of it running; starts and runs ok. If I wait longer, it stumbles on startup till the air runs out of the lines. I have not seen any leaks of fuel that may indicate where air may also be leaking in. Any other clues where ait may be able to get in the system? Thanks
Black smoke indicates: 1) Too much fuel for the amount of available combustion air or, 2) Not enough combustion air for the amount of fuel delivered. Sounds to me like you have a fuel delivery issue, which could include a dribbling injector. Does your air filter check okay? Can you smell any diesel fuel in your lube oil?
When you say "stock fuel tank is totally over the engine", meaning, fuel tank is higher than engine?
Air filter checks out ok. The oil was pretty normal. Oil level was just a trace high. Since I just bought it, not certain if they may have slightly overfilled it at a oil change. Oil did not smell like extra fuel was dumped into the oil pan. Going to see how I can do an injector spray pattern; without any hi tech equipment.
The stock fuel tank is located higher than the engine or fuel filter.
Ok, then by simple physics, gravity, doesn't that negate the possibility of air entering the fuel delivery system causing your problem? And I don't have a clue at this point what is causing the problem, only trying to eliminate possibilities.
Lube oil can become diluted with fuel from dribbling injectors, though not enough to raise the oil level noticeably. Oil analysis is the only sure way to tell, but sometimes there is a faint odor of fuel that gives it away. (I didn't mean to imply there was fuel dumped into the oil pan). You can perform a crude pop test by removing the injectors and reattaching to the hard lines and crank the engine for one or two revolutions. Coffee filters give a good representation of the spray pattern but that's inconsequential at this point. What you will be listening and looking for is a pronounced "squeak" or "chirp" and no drips.
Good call on the injectors. If it was mine, I'd be finding some work, adding some fuel additives, burning up the old fuel and running a clean tank through it. On second thought, maybe use the old fuel to start a bonfire and just start over with some B20 with extra additives, just use it up right away and put clean dino oil back in before you let it sit. If it doesn't change after a tank of new fuel with juice, then pull the injectors...