Westerbeke not holding full RPM under load.

[SVEquanimity]

Hello,

First time poster here. I've tried looking around at old posts, but haven't found a solution to my issue so far, so here it goes. I have a 28' sailboat with a 1989 Westerbeke 12b Two diesel engine in it.

Here are the symptoms I've been having for a few weeks:
1. Motor starts up and revs up to 3000 rpm fine while in neutral
2. While under load, the motor will get up to about 2500 rpm and hold it for anywhere from 5-30 seconds before dropping RPM in a way that sounds like it is being throttled back
3. The RPM will fall back to 1500, sometimes lower. It then will oscillate between 1500 and 2000 somewhat regularly if I leave the throttle down.
4. If I throttle back, it can motor along at 1500 RPM without a hiccup. Anything higher will bounce up and down between the higher RPM and 1500.

I have tried replacing 2 of the 3 fuel filters. I have used SeaFoam to try to clean the fuel system out. I checked the air intake and it seems clean.

I haven't checked the intake at the tank, maybe it could be gunked up?
I haven't checked the injectors, because I don't have any experience with those...

Any thoughts would be appreciated!

Cheers.

Erik
SV Equanimity
Islander 28

[DeepFrz]

Certainly sounds like fuel flow problem all right. Seems you are on the right track.

[mlydon]

Check your lift pump as well - if it’s failed, the motor will limp along under (weak) injection pump pumping.

Easiest method to check fuel delivery, shy of a vacuum gauge, is to remove the return line at the tank and stick it in a jar - you should have decent return flow - a steady trickle at the least.

What filer didn’t you change?

[SVEquanimity]

The filter I haven't changed is the 2nd in the line. It's the filter in the lift pump. It is in an extremely hard to access location... of course. I'll take another look down there this evening and see if I can pull the filter out.

I know the lift pump is working because I can hear the fuel returning to the tank when the engine is priming before start.

Cheers,

Erik
SV Equanimity
Islander 28

[Mike6040]

Heck air vent on fowl tank

[ferrailleur]

If you have an electric fuel pump, you hear it click when the ignition is on. There is a filter built in that small electric fuel pump. It seems that you didn't change that one.... It is the first in line from fuel tank-to water sepataror-to fuel filter before injector pump...

[SVEquanimity]

Originally Posted by Mike6040

Heck air vent on fowl tank

Could be... I haven't checked it yet. I'll take a look.

Originally Posted by ferrailleur

If you have an electric fuel pump, you hear it click when the ignition is on. There is a filter built in that small electric fuel pump. It seems that you didn't change that one.... It is the first in line from fuel tank-to water sepataror-to fuel filter before injector pump...

Yeah that is all correct. And the fuel riser pump works while ignition is on. I tried pulling the filter out, its just in a really tight spot. Here is the diagram:Screen Shot 2019-09-06 at 12.24.30 PM.png Views: 72 Size: 142.7 KB ID: 199292" style="margin: 2px" />
The filter I haven't changed is part 9. Upstream of this whole deal, there is a filter/water separator, which was totally nasty when I changed it, so it's possible to assume the 2nd filter in the line wouldn't be much better.

Cheers,

Erik

[River Cruiser]

Change the filter on the pump. After that if you’re still having problems it’s likely sucking air or has a restriction, the pickup tube in the fuel tank may have a fine screen on the end that can plug. Let us know what you find.

[clakiep]

I had a nerverecking similar problem some years ago. The Mercedes diesel would start an run on idle. Under load, after a while it would rev down and stop. It would restart with no problem. Worst, sometimes it would run for a longer period and than stop. After checking filters and lines, and have the injection pump serviced, I finally found the insignificant problem : a rubber fuel line from tank to pump had a tiny fillet inside loose. Depending on fuel flow and mood it would flap out and block the flow.

[SVEquanimity]

Originally Posted by clakiep

I had a nerverecking similar problem some years ago. The Mercedes diesel would start an run on idle. Under load, after a while it would rev down and stop. It would restart with no problem. Worst, sometimes it would run for a longer period and than stop. After checking filters and lines, and have the injection pump serviced, I finally found the insignificant problem : a rubber fuel line from tank to pump had a tiny fillet inside loose. Depending on fuel flow and mood it would flap out and block the flow.

Thanks for the insight. It's worth keeping an eye out for.

The weird thing about this issue is the relatively predictable behavior... under load, the motor makes it up to 2500 normally holds for a few seconds then drops down to 1500. It has never fully died on me. This causes me to believe that anything restricting the flow must be more stationary than a piece that may or may not get in the way... like floating debris in the fuel tank or a clogged hose.

[SVTatia]

Is the fuel tank vent clear?