Any diesel guru's out there? Have a question

[kito]

Decided to fire up the diesel on my project boat (Yanmar ysm12). I drained all the old fuel, changed oil, installed a new fuel filter, rebuilt the water pump and put new belts on. After bleeding the fuel lines it finally cranked up. This is great news since the PO couldn't get it started (this was his project boat that he gave up on). Anyway, it ran ok with no smoke. The problem I was seeing is erractic rpm's. At half throttle it would slowly build up rpm and then slow back down and back up again. When I finally got it up to full throttle it ran nice and smooth for quite a while. When I backed off the throttle it would be erratic again. It seems like I have to baby the throttle to get it up to full rpm's. It's probably the injector pump, which I rather not mess with if possible. Would something as simple as a can of Seafoam be of any help?

 

[kloudie1]

Fuel delivery or governor are the lead possibles, with fuel delivery being the most probable case.. Banjo fittings or any hose clamps on the suction side of the "lift pump" leaking minute amounts of air, or the little mechanical diaphragm pump that feeds the high pressure injection pump. Try bleeding again by cracking the delivery side of the injector and pumping with the finger lever on the lift pump until there are no bubbles after you've checked/tightened the banjos and made sure the o-ring on the fuel filter at the engine is OK.. Make sure there are no small cracks in the fuel hose from the tank to the primary filter... Sometimes you have to turn the engine a half turn or so to get enough "throw" on the finger lever to get a useful pump stroke.
I don't know how long she sat idle or what condition the oil was in, but if neglected with a really dirty oil, you could have a sticky governor. Good clean oil and running it under load can cure that after 3-4 hours, if you are lucky.
What engine speed are you looking at when it becomes steady? Is it loaded or unloaded?

EDIT: Not a guru, but above was written after careful consultations with tea leaves and wooly booger coat thickness..

 

[Benny17441]

It does sound like fuel delivery problem. When dealing with old diesel fuel it is recommended to wear rubber gloves to avoid bacterial infections. Just removing the old fuel may have left behind some globs of residue. Remove the fuel hose to the tank and blow back some compressed air to clear any obstructions in the tank pick up tube. Make sure that the flow of fuel by gravity from the tank is adequate and continuous. I'm not familiar with your particular engine but in some of the Yanmars it can be hard to properly bleed the fuel lines. Bleed not only at the secondary filter but also go to the bleed screw at the high pressure pump to remove any trapped air.

 

[kito]

Thanks guys. I will mess with it again today. I found out I was bleeding the wrong connection on the filter. I was only bleeding at the injector pump. I will do the Seafoam too. Apparently the injector pump is built to very close tolerances with some lap fitting. Hoping the Seafoam will eventually clean things up. I have no tach but the governor needs some adjusting too. I am guessing at full slow idle I was seeing maybe 100 rpm...very slow. I believe the spec says 700 rpm. All was ran yesterday with no load. Boat is on the hard so didn't want to turn the shaft much. I did shortly just to see if the transmission worked though.

 

[Sailm8]

I had a similar problem with my 1gm10 years ago. Turned out to be gunk in the pick up tube in the fuel tank. It has a small screen over the inlet which I removed and blew out the crap in the tube. Ran great after that.

 

[kito]

I had a similar problem with my 1gm10 years ago. Turned out to be gunk in the pick up tube in the fuel tank. It has a small screen over the inlet which I removed and blew out the crap in the tube. Ran great after that.

Thanks for the tip. I will do that too. Just wish it was more accessible to get to.

 

[Manureva]

On the high pressure pump where the linkage gets hooked up, make sure that the fitting on the bottom is tight. The linkage could have slipped to, unscrew the linkage at the pump, tight up the pin with a flat screw driver, pull the linkage tight and refasten it. If this don't work, you most likely have some thing caught under the pin in the pump where the linkage is, just unscrew and take the needle out check to make sure it is still in good shape. These fuel pump are different than the other, the needle blocks a hole in the wall of the pump to regulate how much fuel goes to the injector. The tighter it is the more fuel goes.

 

[capta]

It is called hunting when a diesel engine runs, but the rpms will not stay steady. It is most often caused by air intrusion, especially if you can reach full no load rpms. If you had a fuel delivery problem, you would not be able to reach full no load rpms. Check all your fuel line connections. If you have used thread tape, a fuel line connection is not a proper place for it and I would suggest buying a bottle of Indian Head shellac (though specifically made for gas engines, it works equally well on diesel) and redoing the threaded connections. As you have already found, bleeding is also very important, but air intrusion into your fuel lines can be a difficult, though usually not expensive, thing to remedy.

 

[kito]

I messed with the diesel today again and re-bled the fuel lines and poured some Seafoam in the tank. After some cranking and some white smoke coming from the mixing elbow area, she finally started and ran like a champ. I could throttle up and down smoothly and held it's rpm at mid throttle. Now for the bad news....my water pump is leaking after my rebuild. I rigged up a hose to pull from a tub of water on the ground and it couldn't do it even after I primed it. I then hooked a garden hose to the intake (low volume) and got leakage around the impeller plate. I will pull it off and flip the plate and see if that helps.

 

[Ian McGain]

While you are at it, it might do you a lot of good to change out the mixing elbow. Good idea on the water pump. That was the answer to my loss of prime on my YSM12. I ended up buying a new back plate and several gaskets.

 

[kito]

Thanks Ian. Yeah, the paper gasket just ain't enough for a worn impeller plate. Have you changed out a mixing elbow before? The smoke from that area did concern me. Didn't smoke after it cranked up though. I found one online for $138....just wondering how much a p.i.t.a. it is to change out. I am not exactly a small guy and have a bad back

 

[rardiH36]

Something outside of the box here, although previous suggestions are more likely to be of use:

Be sure that the throttle itself isn't self-relaxing. For my 1979-80 Yanmar 2QM20 throttle, inside the binnacle housing I installed an adjustable set screw to provide friction against the throttle shaft to prevent the spring tension on the engine side of the cable from self reducing the rpm setting. The rpms might otherwise fluctuate between 2200 and 1500. I have to re-tension this screw every six months or so. When it isn't tight enough, my engine won't hold the expected rpm's even though a visible change in the throttle position isn't really evident.

 

[Ian McGain]

On the mixing elbow. Was not tough to do. The hardest part was taking the cabinet apart to get to the elbow. I purchased all three parts as the whole thing was frozen together and would not come apart. While I was in there, I also replaced the sink raw water pump facet, which was broken and would not work. The reason I changed mine was that it snapped at the all-thread, filled the cabin with smoke and resulted in my first tow.

 

[kito]

Dang, I just redid my galley. I hate to think I need to rip it out again. After further inspection, there seems to be more water leaking than just from the water pump. Since there was light gray smoke coming from the elbow area I hope that is the source for the other leak. I hate to think I have a cracked block from water freezing. This thing has sat for a few years. Anyone know if the ysm12 has freeze plugs and if so about where are they located?

 

[kito]

Well, messed with the boat again tonight. Thought I would take off the mixing elbow and see why I was getting exhaust from it. It was easier than I though.......since the connecting nipple was totally rusted out. It was just sitting on top . I was able to remove the vertical riser fairly easy by reaching over the top of the engine. Didn't have to tear out my galley anyway. Looks like TOAD has all 4 parts I need for around $290. I am replacing all water line hoses too. Can someone tell me if 1/2" and 5/8" hose work on the engine nipples? I know it's probably metric nipple sizes on the engine but should work. The 2" exhaust hose from the elbow to the muffler is toast too. good thing is that the long length from muffler outlet to the thru hull looks newer and seems ok.