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Old 08-09-2014, 11:12   #1
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Diesel Struggles Under Load

Howdy everyone, I'm having a problem I haven't been able to find an answer to yet. A few weeks ago I was out when suddenly my engine lost most of it's power. I made it back to the dock ok and haven't moved her since.

The engine starts and runs at idle just fine, but when I put her in gear, forward or reverse, my revs drop instantly the second she shifts, pulling about half of what she just was. The motors a westerbeke, I believe a 35b, it was repowered before I bought it. I've seen this problem in a few places, but never found a definitive answer.

I'm getting fuel flow throughout the whole system, I replaced my primary fuel filter and cleaned my secondary, and tightened my v belt. My next stop is going to be removing the fuel tank pickup, which I've blown through backwards already, then check the pressure up the line. I've also seen something about the exhaust manifold and elbow getting clogged, but I don't think it would be quite so instantaneous if it was an exhaust issue. Any help guys?
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Old 08-09-2014, 11:17   #2
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re: Diesel Struggles Under Load

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Originally Posted by strqaightv8 View Post
Howdy everyone, I'm having a problem I haven't been able to find an answer to yet. A few weeks ago I was out when suddenly my engine lost most of it's power. I made it back to the dock ok and haven't moved her since.

The engine starts and runs at idle just fine, but when I put her in gear, forward or reverse, my revs drop instantly the second she shifts, pulling about half of what she just was. The motors a westerbeke, I believe a 35b, it was repowered before I bought it. I've seen this problem in a few places, but never found a definitive answer.

I'm getting fuel flow throughout the whole system, I replaced my primary fuel filter and cleaned my secondary, and tightened my v belt. My next stop is going to be removing the fuel tank pickup, which I've blown through backwards already, then check the pressure up the line. I've also seen something about the exhaust manifold and elbow getting clogged, but I don't think it would be quite so instantaneous if it was an exhaust issue. Any help guys?
What color is your exhaust? Is it different than before you had your power reduction?
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Old 08-09-2014, 11:20   #3
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re: Diesel Struggles Under Load

hmmm... one possibility is a clogged up exhaust elbow. also, have you tried cracking off each injector nut? do they all make a difference or does cracking one off not make a difference?
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Old 08-09-2014, 12:01   #4
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re: Diesel Struggles Under Load

Exhaust is white on start up then fades away, just like it always has. It might take a little longer than usual, or it might just be because I'm actually paying attention to it for once.

All three injectors squirt fuel and bog down the motor when cracked, I talked to a diesel mechanic at my work who said to crack them again and see if one of them needs to spin off further than the others to produce fuel( I.e. Half turn vs quarter turn.)

I suspected the exhaust elbow, but took off the exhaust outlet hose and jammed my fingers up in it, they came out black but I didn't notice any large deposits. That's not to say they aren't further in, or possibly inside the exhaust manifold. I'm trying to reach all of my "easy" solutions before I drop $600 in parts and gaskets
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Old 08-09-2014, 12:21   #5
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re: Diesel Struggles Under Load

The most likely cause and easiest to diagnose is a fouled prop. Check to see if something's caught on it or if there is growth. It doesn't take much to create resistance.

We went through the same stuff two years ago, hauled the boat, re-pitched the prop and gave it a good cleaning... problem solved. Now I clean and scrape it once a month.

More recently, I noticed a vibration under load and slight change of rpms. Looked for answers everywhere. Then when I happened to dive under the boat, 'noticed a piece of rope caught on the shaft. The rope cutter had done it's job, but a small piece of line was still caught.
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Old 08-09-2014, 13:58   #6
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re: Diesel Struggles Under Load

I was about to suggest the exhaust/mixing elbow too. I just read recently someone else who was having similar issue. Once they changed it out, they took the old one and cut it in half to show the clog was farther into the elbow.

That other guys response after he cut the elbow:
"The injected sea water passage was very clean, however the exhaust gas passage was completely blocked by solid carbon deposit. Approx. 40mm dia original passage was filled with the deposit only leaving less than 10mm opening. This is after 5 years and 1500 hours enigne"
(His engine is a Yanmar 3YM-20)
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Old 08-09-2014, 14:14   #7
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re: Diesel Struggles Under Load

I would start with the simple! A sudden power loss to me means a fuel problem. Even though you changed the filters you have not really ruled out that it isn't a fuel problem.

Get a nice clean pail of fuel and stick the fuel suction line in and see if the the problem goes away.
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Old 08-09-2014, 16:26   #8
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re: Diesel Struggles Under Load

Dove under and cleaned the prop, no change, I had thought about this already but I just cleaned the shaft about a month ago

Checked it with a clean jug of fuel, no change

I guess the next step is tear into the exhaust elbow and order a new one
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Old 09-09-2014, 19:11   #9
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re: Diesel Struggles Under Load

I had a similar problem that turned out to be a clogged air filter, have you checked this first? everything was normal until I put the diesel under load and that was when it blew smoke and would not deliver any thrust.
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Old 09-09-2014, 21:58   #10
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re: Diesel Struggles Under Load

Sort of sounds like the governor may not be working right. As it starts easy compression is probably good. So just going into gear without a speed increase causes it to die. I assume that more throttle does nothing. My guess is a spring is broke on the injector limiter part of the governor. Cheap but a small pain to get too.

Or discharge elbow, but at idle it should be fine. I would expect that to show up at higher rpm, not at idle.

Water in the fuel could cause that too, but it would be hard starting too.

So things it could be are:
Clogged discharge elbow, take it off and run a small chain (dog chain) back and forth through it. But not normally a problem at idle.

Bad fuel. I would replace the one filter you only cleaned.

Broken spring on injector limiter. Hum. Does it rev up in neutral??

Broken rings/low compression (remove oil fill cover when running), you would get lots O grey smoke out of the oil fill if it bad/broken rings. Generally low compression would first been seen as hard starting, even when warm.

Clogged air filter would do it too.
Clogged return line, low percentage failure there.
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Old 10-09-2014, 04:53   #11
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re: Diesel Struggles Under Load

No air filter on the boat, just the sound dampener or whatever it's called over the intake


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Sort of sounds like the governor may not be working right. As it starts easy compression is probably good. So just going into gear without a speed increase causes it to die. I assume that more throttle does nothing. My guess is a spring is broke on the injector limiter part of the governor. Cheap but a small pain to get too.

Or discharge elbow, but at idle it should be fine. I would expect that to show up at higher rpm, not at idle.

Water in the fuel could cause that too, but it would be hard starting too.

So things it could be are:
Clogged discharge elbow, take it off and run a small chain (dog chain) back and forth through it. But not normally a problem at idle.

--Dismantled my exhaust system yesterday, no buildup in any components, including inside the exhaust manifold

Bad fuel. I would replace the one filter you only cleaned.

--I'm not terribly worried about that filter, it's the secondary in between my primary and injector pumps, but if I can find a replacement easily I'll change it

Broken spring on injector limiter. Hum. Does it rev up in neutral??

--full range of revs in neutral, around 4k top end, when I put it into gear it bogs down slightly and limits revs to 2-2.5k. It reaches this level where it should, around halfway up my control lever's throw, but the last half of the throw sees no additional increase. And it's not the linkage either here, I've adjusted my screws and worked it manually, no change. I do remember reading about someone with a similar problem and it was the spring that caused it, it's worth looking into, I'll see what I can do with it later today

Broken rings/low compression (remove oil fill cover when running), you would get lots O grey smoke out of the oil fill if it bad/broken rings. Generally low compression would first been seen as hard starting, even when warm.

--ditto for checking this later

Clogged air filter would do it too.

Clogged return line, low percentage failure there.
--it's worth a shot, I can take it apart and blow through it

The way I'm thinking about it is either air or fuel is restricted somewhere. So it runs fine in neutral but when I put it under load the engine expects an increase in fuel/air throughput. After examining the air intake and exhaust system I'm fairly confident that's not the issue. So that leaves fuel

My next step was going to be start replacing all my fuel lines and my pumps



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Old 10-09-2014, 05:44   #12
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re: Diesel Struggles Under Load

'Just curious, did you go under and check the prop to see if it was fouled?
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Old 10-09-2014, 05:55   #13
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re: Diesel Struggles Under Load

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'Just curious, did you go under and check the prop to see if it was fouled?

Sorry, I thought I had mentioned it in a previous reply. Nothing was visibly tangled or caught, there was a good growth of barnacles on the prop I scraped down, but it didn't change anything. After thinking about it, it could definitely be something with the prop, shaft, or transmission, and that's why nothing goes wrong until all of those things engage


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Old 10-09-2014, 06:51   #14
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re: Diesel Struggles Under Load

On your clean jug O fuel operation, did you stick 2 new lines straight from the pump and return into the jug? Can you bypass all your filters?

As previously mentioned, I like IP gov spring, exhaust restriction ... Just for fun, is it too much trouble to unbolt your shaft?

You like fun don't you???
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Old 10-09-2014, 06:57   #15
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re: Diesel Struggles Under Load

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On your clean jug O fuel operation, did you stick 2 new lines straight from the pump and return into the jug? Can you bypass all your filters?

As previously mentioned, I like IP gov spring, exhaust restriction ... Just for fun, is it too much trouble to unbolt your shaft?

You like fun don't you???

I did not run two lines, I just put the suction line in and let the return run to the stock tank, didn't think it would make much difference. I can bypass the first filter but not the second, they have some specialty hoses and fittings from my primary pump all the way through the injector pump.

It's not a terrible job to unbolt the shaft, I've got pretty good access, and it shouldn't be too stuck, I just replaced the coupler about 7 months ago. I like the idea though, I hadn't thought of it. At the very least it would confirm it's nothing to do with prop.

And I bought a 30 year old boat, of course I like fun




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