Loss then surging of rpms

[Steve s]

The diesel on my Beneteau 393 has been operating fine except for today. After about 20 mins of motoring the engine began to go thru this cycle of dramatically losing all rpms (almost stalling). Then surging back to the original rpm This would go on for 5 to 10 mins then it would run fine for about 5 mins, then go back into the wild swings.

We made it back to the mooring but this needs a fix.

Any ideas on what the cause is ?

Thanks

Steve S

 

[Don S/V ILLusion]

Only two common causes - air in the fuel line or a clogged filter/screen.

Assuming you are not about to run out of fuel as the cause of air, it could be a fitting which has loosened anywhere in the fuel train.

If not the above and you have good fuel flow through a clean filter, it could be a clogged pick-up tube screen in the tank.

There are other possibilities but those are the most common.

 

[Rick]

Concur. Most likely a clogged filter and the easiest thing to troubleshoot. All you need is a spare.

 

[Stu Jackson]

When was the last time you serviced your engine & its components?

 

[zeehag]

air leak or clog in diesel lines. every time. maintenance fixes that nicely.

 

[Terry in Naples]

loss of power then surge

sounds to me like a clogged fuel filter. I had a truck did the same thing.

 

[reworb]

My Beneteau 311 was doing the same thing. It was a clogged fuel filter. I would change both the Racor and the one on the engine.

Also how old is the fuel in the tank if it's old it could have a lot of "gunk" in it in which case you will clog your new filters. You may want to look inside your tank, if the fuel is pretty new and the tank looks good it was just time to change the filters. If not then you may want to invest in having the tank cleaned or one of the chemical fuel treatments.