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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 05-06-2012
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Runaway Yanmar 2qm15 HELP!

A few month back bringing Kare Knot down the intercoastal a slow oil leak caused my oil level to run low. Since it was coming from the back of the engine I decided to pull the engine and change all the seals and gaskets. I boomed the diesel into my tender and lugged it tom my garage. In the process of cleaning I broke a ring and decided to change the rings. Ordered one of those $15 dollar honing tools and commenced to destroy the inside of my cylinder walls (don't try to do this yourself!) Thinking that I had done a good enough job I reinstalled the engine (not fun!). Any way after a few days of trying to get the fuel lines to bleed the 2 banger came to life. Like 3500 rpm of life!!! Anyway if you've never had this happen it will scare the crap outta you! Finally covered the intake and the engine reluctantly sputtered to a stop. Decided to drink a beer and give it a once over. Nerves calmed I tried again with the same results. My first intuition was it was the injector pump which I took apart as part of rebuild (allso not a good idea!). So took it to an injection specailist and forked over $200 for my precision tuned pump. Installed the pump and holy crap it ran away again. Now my worst fear set in... my crappy honing job! I winched out the engine again and brought it for a professional honing. The checked the wall diameter, ring gaps mating surfaces and put a nice cross-hatch on the walls. Meanwhile smeone stole my $2000 dingy and engine! Anyway winched the motor in for the second time. Checked ever detail while reassembling. Started her up and it fricken ran away again. I'm out of ideas... Pulled the injectors and will have them tested this week. If this doesn't fix it I'm all out of ideas. Anyone with any other ideas I sure would appreciate it! Here's a list of what I chaged so far:

New rings
Front & rear main bearings
Rod bearings
Front & rear seals
Injector mating seals
New head gasket (well all new gaskets)
Replaced the soft fuel lines.
Rebuilt injector pump
2 quarts of oil
Valve stem seats

Professionally rehoned and certified valve steams, seat ok, ring gap and mating warp ok

Now just some notes, blowing blue smoke. Disconnected fuel supply and the engine stopped. The spring between the injector pump and the throttel inhibitor seems looser that it should. Moving the throttle while running does not impact speed.

Any ideas would be greatly appreciated!!!!!!!!!!

Thanks EZ
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Old 05-06-2012
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Re: Runaway Yanmar 2qm15 HELP!

Is the throttle connected properly to the engine? Is idle really idle?
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Old 05-06-2012
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Re: Runaway Yanmar 2qm15 HELP!

Plugged crankcase breather? excessive blow-by? Lift pump diaphram, it it has one, torn, allowing fuel to mix with crankcase oil? Excessive injector pump pressure? "weak" injector
springs? Injector pump not really fixed? Did it run Ok before you worked on it?

Paul T
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Old 05-07-2012
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Re: Runaway Yanmar 2qm15 HELP!

Thanks for your replies. First the throttle cable is not connected at this time but I've turned it while the engine is running and it will rev faster but not slower (strange). I have had the breather cover completely off while the engine was running an it made the engine run faster because I could no longer control the air supply by way of the air intake. Not sure what you are talking about when you say lift pump diaphram? The oil pump on the 2qm is external on the flywheel side and driven by the cam shaft. Yes the engine ran very well before.
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Re: Runaway Yanmar 2qm15 HELP!

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Originally Posted by miamiz View Post
Thanks for your replies. First the throttle cable is not connected at this time but I've turned it while the engine is running and it will rev faster but not slower (strange). I have had the breather cover completely off while the engine was running an it made the engine run faster because I could no longer control the air supply by way of the air intake. Not sure what you are talking about when you say lift pump diaphram? The oil pump on the 2qm is external on the flywheel side and driven by the cam shaft. Yes the engine ran very well before.
Not sure what kind of lift pump you have. Some older ones had a diaphram activated by a lobe on the cam. A torn diaphram might leak fuel into the crankcase diluting the engine oil, "over filling" the crankcase, but that is probably a stretch? You said you took the injector (high pressure) pump apart
which could be risky business. As the engine ran fine before you took the pump apart I would think the pump is your prime suspect as the injectors are pretty stable, "going bad" very gradually, if at all. Perhaps if you go to a well respected shop and bought a re-built pump, giving your old one as a "core", might do the trick?

Paul T
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Old 05-07-2012
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Re: Runaway Yanmar 2qm15 HELP!

I think the OP said in his original rundown that the runaway problem came up after replacing engine gaskets, honing, and rings, but before he messed with the high pressure pump. He opened that up while trying to fix the runaway.
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Re: Runaway Yanmar 2qm15 HELP!

Thanks Paul. Just got back from the injector shop. Had my injectors flow tested and they are fine. The injector pump was professionally rebuilt also. The lift pump on the 2QM is external. Now that kinda points me to two possible culpits... Either there is blow by on the pistons or something assembled wrong on the throttle internal linkage. Like I said the spring that goes from the throttle inhitor to the injector pump arm seems looser than is should. Thought I remember it being pretty tight to get off... God I miss my memory!
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Re: Runaway Yanmar 2qm15 HELP!

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Originally Posted by miamiz View Post
Thanks Paul. Just got back from the injector shop. Had my injectors flow tested and they are fine. The injector pump was professionally rebuilt also. The lift pump on the 2QM is external. Now that kinda points me to two possible culpits... Either there is blow by on the pistons or something assembled wrong on the throttle internal linkage. Like I said the spring that goes from the throttle inhitor to the injector pump arm seems looser than is should. Thought I remember it being pretty tight to get off... God I miss my memory!
Maybe the spring was stretched when removing it? I still suspect something wrong with the pump?

Arf, " My first intuition was it was the injector pump which I took apart as part of rebuild (allso not a good idea!). " Not sure when exactely he did the pump? If there was that much blow by it might be hard to start?

Paul T
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Re: Runaway Yanmar 2qm15 HELP!

After thinking, the injector pump is external but has a lifter arm into the crank case and actuated by the cam. However, having just rebuilt the engine and new oil, I don't think that on first start there would be dilution yet... The runaway was immediate. Good point on hard starting - in this case it starts easy which points us away from low compression. Could it be that the rings need time to seat? If I control the throttle by partially blocking the air intake and let it run for a while would that damage anything....would they eventually seat? there seems to be allot of vacume in the head (that may be normal) but after I shutoff the engine it takes a heavy 3-4 second breath thru the intake. But I thought if something were creating too much vacume that it could suck oil up or the reverse if there was too much crank case pressure...
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Re: Runaway Yanmar 2qm15 HELP!

Quote:
Originally Posted by miamiz View Post
After thinking, the injector pump is external but has a lifter arm into the crank case and actuated by the cam. However, having just rebuilt the engine and new oil, I don't think that on first start there would be dilution yet... The runaway was immediate. Good point on hard starting - in this case it starts easy which points us away from low compression. Could it be that the rings need time to seat? If I control the throttle by partially blocking the air intake and let it run for a while would that damage anything....would they eventually seat? there seems to be allot of vacume in the head (that may be normal) but after I shutoff the engine it takes a heavy 3-4 second breath thru the intake. But I thought if something were creating too much vacume that it could suck oil up or the reverse if there was too much crank case pressure...
Maybe when re-assembling the engine you reversed the manifold gasket or a flange somewhere and the engine is pulling air from within the crankcase bringing oil with it? The 3 to 4 second "breath" would indicate excessive pressure or vacuum in the crankcase. If it is breathing in the vacuum may be pulling oil along with the air. If breathing out oil may be being pushed up the breather tube into the intake manifold. If the inside of the manifold has a lot of oil in it that may be the cause. However, the fact that you can stop the engine with a rag in the intake may dispell that theory? A rebuilt pump out of the box would be an easy try.

Paul T
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