Suck Squeeze Bang Stall
June 6, 2012 5:48 AM Subscribe
Why is my diesel engine stalling every time I put a load on it?
I have a sailboat with a Westerbeke 12C-Two engine (circa year 2000). The thing has been bulletproof for the past 6 or 7 years until this weekend. I know just enough about diesels to be dangerous, so you can give me the 200-level talk.
It runs fine in neutral, at any RPM. When I put it into gear, I can manage to keep the shaft spinning at idle or just above, but if I go any higher than that, it gracefully powers down and stalls. Sometimes I can manage a minute or two at a midrange RPM, but the result is always the same- power down and stall. When it is running in gear, it's kind of quavery, rather than a steady thrum. I can get the engine restarted after one of the stalls, but it chokes for awhile and I have to kind of flutter the throttle until it's happy in neutral again.
I've changed both the primary and secondary (coarse/fine) fuel filters and removed all the lines on the fuel system to ensure they're free of any blockages (blew through them). There's fuel in the tank. The propeller shaft spins free by hand, there's fluid in the transmission, and there's nothing fouling the prop. There is no air filter on this particular model, but the intake is clear and free of any blockages as far as I can tell.
It sounds to me like it's not getting fuel, but only while under load, since it's quite happy in neutral. I was on a cruise when this happened, so the boat isn't in my home port with my regular mechanic, so I'd like to be as knowledgeable as possible when dealing with a new guy in a weird place, since I've run out of everything I know how to fix.
Many thanks!
I have a sailboat with a Westerbeke 12C-Two engine (circa year 2000). The thing has been bulletproof for the past 6 or 7 years until this weekend. I know just enough about diesels to be dangerous, so you can give me the 200-level talk.
It runs fine in neutral, at any RPM. When I put it into gear, I can manage to keep the shaft spinning at idle or just above, but if I go any higher than that, it gracefully powers down and stalls. Sometimes I can manage a minute or two at a midrange RPM, but the result is always the same- power down and stall. When it is running in gear, it's kind of quavery, rather than a steady thrum. I can get the engine restarted after one of the stalls, but it chokes for awhile and I have to kind of flutter the throttle until it's happy in neutral again.
I've changed both the primary and secondary (coarse/fine) fuel filters and removed all the lines on the fuel system to ensure they're free of any blockages (blew through them). There's fuel in the tank. The propeller shaft spins free by hand, there's fluid in the transmission, and there's nothing fouling the prop. There is no air filter on this particular model, but the intake is clear and free of any blockages as far as I can tell.
It sounds to me like it's not getting fuel, but only while under load, since it's quite happy in neutral. I was on a cruise when this happened, so the boat isn't in my home port with my regular mechanic, so I'd like to be as knowledgeable as possible when dealing with a new guy in a weird place, since I've run out of everything I know how to fix.
Many thanks!
Response by poster: The fuel pump reprimes automatically, so I'm reasonably sure that they're reprimed. The exhaust is invisible like normal.
Notsnot: the fuel pump was my guess as well, but can a fuel pump only sort-of fail?
posted by zap rowsdower at 6:11 AM on June 6, 2012
Notsnot: the fuel pump was my guess as well, but can a fuel pump only sort-of fail?
posted by zap rowsdower at 6:11 AM on June 6, 2012
What you describes sounds like it's not getting proper fuel pressure. Either the pump isn't produce a large enough flow rate at the right pressure or you have lines that are collapsing under the suction. The amount of fuel needed is much greater when under load.
Think about it, you can spin the pedals on your bike very fast when it's upside down and you're working on it. But get on the bike and head up a hill and you'll have to work a lot harder. The same basic logic applies with an engine freely spinning in neutral versus when in gear trying to push the prop through water.
The fuel's got to get out of the tank and to the engine. There are plenty of points along the way that can affect the process. Like gunk in the tank that only gets picked up when the suction pulls hard enough to lift it. Or that same suction pressure collapsing the hose from the inside. You've already replaced filters and if they didn't show any gunk then it's probably not something inside the tank.
Since it's 12 years old, I'd replace the fuel lines. Fuel is a solvent and will eventually degrade the hoses. Most aren't rated for more than 5 years, but often last longer. They can look fine from the outside but be weak and spongy on the inside.
You'd probably want to put a fuel pressure gauge on the line to monitor how the system is performing. You'd have to refer to Westerbeke service info to find out the idea pressures, and where to attach them to the fuel system. Be careful, some systems can deliver fuel at high enough pressures as to cause injuries.
That would leave the fuel pump. It's entirely possible that can no longer able to deliver proper flow and pressure.
posted by wkearney99 at 6:58 AM on June 6, 2012
Think about it, you can spin the pedals on your bike very fast when it's upside down and you're working on it. But get on the bike and head up a hill and you'll have to work a lot harder. The same basic logic applies with an engine freely spinning in neutral versus when in gear trying to push the prop through water.
The fuel's got to get out of the tank and to the engine. There are plenty of points along the way that can affect the process. Like gunk in the tank that only gets picked up when the suction pulls hard enough to lift it. Or that same suction pressure collapsing the hose from the inside. You've already replaced filters and if they didn't show any gunk then it's probably not something inside the tank.
Since it's 12 years old, I'd replace the fuel lines. Fuel is a solvent and will eventually degrade the hoses. Most aren't rated for more than 5 years, but often last longer. They can look fine from the outside but be weak and spongy on the inside.
You'd probably want to put a fuel pressure gauge on the line to monitor how the system is performing. You'd have to refer to Westerbeke service info to find out the idea pressures, and where to attach them to the fuel system. Be careful, some systems can deliver fuel at high enough pressures as to cause injuries.
That would leave the fuel pump. It's entirely possible that can no longer able to deliver proper flow and pressure.
posted by wkearney99 at 6:58 AM on June 6, 2012
Notsnot: the fuel pump was my guess as well, but can a fuel pump only sort-of fail?
Yes, they can sort of fail and only deliver a fraction of the pressure required. The simplest test is to look up the required pressure, and measure it as close to the injectors as you can. Normally, you'd then work down to the tank, and if you see a big jump in pressure, whatever part of the line you skipped is where the pressure is being lost -- or where a constriction exists.
However, if you are certain that the filters and lines are clear, then I'd start at the fuel pump output and see if it's up to spec. Assuming that all you said is correct (you checked all of the lines, the fuel filters you installed aren't faulty, etc.) then I'd check pressure at the pump, if in spec, I'd check just before the injectors, if that's in spec, we're now looking at something with the injectors or further into the engine.
Hmm, something just hit me. How's the air filter and intake? Limiting the air would have exactly the same effect in terms of power. You'd run rich, rather than lean, but the result would be the same.
posted by eriko at 8:21 AM on June 6, 2012
Yes, they can sort of fail and only deliver a fraction of the pressure required. The simplest test is to look up the required pressure, and measure it as close to the injectors as you can. Normally, you'd then work down to the tank, and if you see a big jump in pressure, whatever part of the line you skipped is where the pressure is being lost -- or where a constriction exists.
However, if you are certain that the filters and lines are clear, then I'd start at the fuel pump output and see if it's up to spec. Assuming that all you said is correct (you checked all of the lines, the fuel filters you installed aren't faulty, etc.) then I'd check pressure at the pump, if in spec, I'd check just before the injectors, if that's in spec, we're now looking at something with the injectors or further into the engine.
Hmm, something just hit me. How's the air filter and intake? Limiting the air would have exactly the same effect in terms of power. You'd run rich, rather than lean, but the result would be the same.
posted by eriko at 8:21 AM on June 6, 2012
My first guess was also fuel, but I see others have covered that. My second thought was air ... but I think if you had an airflow problem, that you'd see blue smoke as the engine stalled (it would be getting a lot of fuel but not combusting completely, and would probably smoke in the exhaust manifold). If you are really sure there's no smoke or oily discharge coming from the exhaust as it stalls, then I'm not sure about the air theory.
The third possibility that comes to mind is compression. But I think you'd also have hard starting and rough idle, not just problems at power, if you had a serious compression issue. (Given that you have a naturally aspirated engine without a turbo.) It's not terribly hard to put a compression gauge on though, just to rule it out. Depending on the layout of the engine and fuel tank, this might be easier to do than replacing lines so it might make sense to do it first.
posted by Kadin2048 at 8:41 AM on June 6, 2012
The third possibility that comes to mind is compression. But I think you'd also have hard starting and rough idle, not just problems at power, if you had a serious compression issue. (Given that you have a naturally aspirated engine without a turbo.) It's not terribly hard to put a compression gauge on though, just to rule it out. Depending on the layout of the engine and fuel tank, this might be easier to do than replacing lines so it might make sense to do it first.
posted by Kadin2048 at 8:41 AM on June 6, 2012
Wkearney99's got a good metaphor for how it can idle but not power up.
We just had a forklift have the same problem. We cleaned out the fuel inlet (nasty), blew out all the fuel lines, tested the pump...turns out in this case there were two pumps - one out of the tank, and one that bolts up right next to the injector rail on the far side of the engine. Check and make sure it's not a case like that.
posted by notsnot at 10:29 AM on June 6, 2012
We just had a forklift have the same problem. We cleaned out the fuel inlet (nasty), blew out all the fuel lines, tested the pump...turns out in this case there were two pumps - one out of the tank, and one that bolts up right next to the injector rail on the far side of the engine. Check and make sure it's not a case like that.
posted by notsnot at 10:29 AM on June 6, 2012
Response by poster: Thanks, all. You're pretty much confirming what I suspected. As notsnot said, there is a secondary pump right next to the injectors. However, that one's driven by the engine itself and is connected to the crankcase, which is definitely beyond my scope. The first (lifting) pump is a 12V deal though, and I can pretty easily replace that. For $200 it seems like something reasonable I can try. All of the flexible lines have been replaced recently (by me), and everything after the lifting pump is a rigid line which again is beyond my scope.
Kadin- yep, no smoke or trouble starting, aside from sounding starved for fuel at start after a stall. I don't think its an airflow issue.
wkearney- thanks for that analogy. That's always how I've thought of it in my head but always felt silly talking to a mechanic like that.
Fuel pump ordered. Let's see what happens...
posted by zap rowsdower at 12:18 PM on June 6, 2012
Kadin- yep, no smoke or trouble starting, aside from sounding starved for fuel at start after a stall. I don't think its an airflow issue.
wkearney- thanks for that analogy. That's always how I've thought of it in my head but always felt silly talking to a mechanic like that.
Fuel pump ordered. Let's see what happens...
posted by zap rowsdower at 12:18 PM on June 6, 2012
A diesel engine will run on a wide range of fuel/air mixtures, unlike a gasoline engine. The way you control power delivery is by means of the amount of fuel delivered - the air intake into a diesel engine is essentially un-throttled.
Therefore, I suspect the governor. Page 65 of the Westerbeke manual shows inspection points for the governor and I will wager $4 that is where your problem lies.
posted by jet_silver at 7:13 PM on June 6, 2012
Therefore, I suspect the governor. Page 65 of the Westerbeke manual shows inspection points for the governor and I will wager $4 that is where your problem lies.
posted by jet_silver at 7:13 PM on June 6, 2012
Response by poster: Problem is fixed- yours (and my) thoughts about a bad fuel pump were essentially correct, though for the wrong reason. Engine had a bad fuel sender sensor, meaning that the lift pump wasn't turning on when it needed to. It would run at idle because the injection pump was strong enough to keep enough go juice in there on its own, but not strong enough to provide enough diesel to run under load.
(This explains why replacing the fuel pump didn't solve the problem)
posted by zap rowsdower at 8:17 AM on June 21, 2012 [1 favorite]
(This explains why replacing the fuel pump didn't solve the problem)
posted by zap rowsdower at 8:17 AM on June 21, 2012 [1 favorite]
I just bought an older sailboat (1996) with a Westerbeke 12C Two, and I am experiencing EXACTLY the same symptoms. I have been scratching my head on this one, and last night I came across your posts...EUREKA!!
Zap, I poured through the parts manual, and I can't find the part you described (fuel send sensor). Can you tell me the part number? Was it difficult to install? Do you suggest I go ahead and replace the fuel lift pump to due to the age the engine (120 hours).
Thank you in advance. I might be able to sail this weekend!
posted by keelz at 4:07 AM on June 28, 2012
Zap, I poured through the parts manual, and I can't find the part you described (fuel send sensor). Can you tell me the part number? Was it difficult to install? Do you suggest I go ahead and replace the fuel lift pump to due to the age the engine (120 hours).
Thank you in advance. I might be able to sail this weekend!
posted by keelz at 4:07 AM on June 28, 2012
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What does the exhaust look like?
posted by gjc at 5:59 AM on June 6, 2012