Strange engine problem

[argalax]

Hi all.

My sailboat has a Westerbeke 42B4 diesel engine.
It starts normally, and can run for hours at cruising speed. Later, when I need to wait for as bridge opening, I would witch between neutral and idle speed for some time. Then, when bridge opens, I would press ahead, but the RPMs wild slowly drop and engine stops. Even at full throttle. Sometimes RPM would fluctuate without giving full power.
Restarting the engine sometime fixes the problem temporarily, until the next bridge...
Very frustrating.

More info:
- In neutral, the RPMs are holding fine, the problem is when engine is engaged.
- Fuel filters are freshly replaced and clean
- Tightened all fuel line clamps, etc. - fuel and air leaks are unlikely.
- Prop is clean

Any suggestions will be greatly appreciated.

Thanks.

[CptLawrence]

Check that plenty of fuel is reaching your nearest filter to the fuel tank. If the filter does not have a bowl on the bottom that you can shine a light through then add some clear fuel line near it to confirm you dont have a problem with the pick-up tube in the tank. Then confirm plenty is reaching the lift pump and/or injector pump. When filters are changed be sure there is not a problem with the o-rings, there shouldn't be any drips or runs. When was the last maintenance done? When was your fuel tank last cleaned? There might be old contaminated fuel giving you problems. Injectors may need to be pulled and tested.

[delmarrey]

It sure sounds like a fuel problem, but the first thing that came to mind was the shut off solenoid.
Check the wire that keeps the fuel solinoid open. It may be loose at one end or the other, or even about to break somewhere in between.
When your running hard it keeps enough current but a slowdown allows it to lose contact.

Another item maybe the freshly changed fuel filer is sucking air into the system and while running slow there's not enough fuel to get going again.

One more thing to check is the mixing elbow, it maybe getting plugged. All suggestions, it's a process of elimination.

[argalax]

Thanks for the replies - helpful.
Looks like I have to clean the fuel tank - primary filter seem to collect sludge quickly.

[Crow]

There's a thread on this over at YBW. A small airleak seems like a common problem, sucking in more air under load. Air intake blockage might be another thing to consider, should lead to black smoke though.

Good luck,
Crow

[dlockhart]

Once upon a time I had a similar problem, let off the fuel and the engine quit, neutral - restart fine - put into gear quit. Put into gear and accelerate fast and may or may not go. Had a rope wound around the prop on that sail drive so tight that it was real hard to remove. Had noticed an ever so slight but not usual vibration at cruise rpm.

[SkiprJohn]

Originally Posted by argalax

Thanks for the replies - helpful.
Looks like I have to clean the fuel tank - primary filter seem to collect sludge quickly.

That'll do it.

[argalax]

Just an update.

Originally Posted by SkiprJohn

That'll do it.

Yes, it did. Cleaned the tank (there was quite e bit of sludge), replaced fuel filters - didn't have problem since.

[Sailorman Ed]

Argalax - glad you found your problem.

I have twin 2 cyl Yanmars, 600 hours, . Brought the boat (new to me) from MD to NC, both engines ran perfectly. Been sittingin a marina fixing other issues, went to take the family out last WE, one starts right up while the second would not fire up. Switched batteries thinking maybe not enough juice - no difference. Used the compression release levers to get one cyl to fire and then would quit. Bleed the fuel lines to the injectors, still no good. Left with 1 engine. Next day moving to a different anchorage, wife says, try the engine, maybe it will work now. I said nothing changed but would give it a try - STARTED RIGHT UP!!!! Ran fine the way back. So what should I be looking for? Runs perfectly while running, has fuel to the injectors, has compression...what am I missing?
Ed

[CptLawrence]

Sounds like it was warmed up by the other engine's heat or maybe the day was warmer. Older diesels with less compression need that heat. Have you checked the glow plugs? They should get power when you turn on the key or turn it backwards or push a button.