Fuel uptake problem

[Jwhy]

After cruising against the wind and long shore off the California coast for several hours, my M25 diesel lost rpm and eventually stalled. I wasn't able to get it going for a significant period period of time without a repeat of the problem.
We turned around and sailed back to port and had a mechanic check the engine. The filters are new, the fuel pump is two years old, the fuel line from tank to filter is new and the tank is clean. The mechanic suspected a problem with the uptake tube and hose, took it out, cleaned it and checked for leaks.
We topped off the tank and found that everything was fine the next day until the tank got down to the two thirds full mark. The stall happened again. We added fuel to the tank which cured the problem. When the tank level dropped to that point again, the stall recurred and was fixed by topping off the tank.

The pick up assembly is a simple copper tube with a rubber tube extension. What can go wrong?

 

[Don S/V ILLusion]

My guess - bad fuel pump. New ones can go bad just like old ones.

 

[SG]

Beyond Don's suggestion, the tank can have crud in it which blocks the pick-up tube (for a bit, then releases, then gets suck-up again?). Your mechanic looked in the tank and it's "clean"?

 

[Jongleur]

Pin hole air leak at that point?

 

[Jwhy]

Yes the tank is clean with no debris or discoloration of the fuel. He removed the intake blew it out and blew into it with the other end capped to see if there was a leak.

 

[SG]

Good. Then it's downstream bad connection, or pump ( as others have suggestd).

Do you have two filters? Initial (maybe Racor with. 30 micron) followed by final finer filter before engine?

 

[Jwhy]

Yes the Racor is the first stop. I drained the bowl and found a tiny amount of water and some cloudy fuel.

 

[Stu Jackson]

Pump. Check the pump.

Just coincidentally:
http://c34.org/bbs/index.php/topic,9526.msg71641.html#msg71641

Our tank is above our M25 engine.

 

[Jwhy]

The mechanic advised a longer pick up tube but that doesn't make sense to me since the tube hasn't gotten shorter in the years I've had the boat and run without a problem.

Stu's link was helpful and explains something I observed. When the engine shut down I opened the bleed valve to release air. I saw the fuel flow vary with the roll of the boat, plenty in one direction and none in the other. It also seemed like the tapping sound the pump makes was less intense.

 

[Charles Erwin]

Rubber extension too long. Insert in tank, something interferes, rubber curls upward. Measure tank depth. Make overall pick up length to 1/2 inch above tank bottom. Consider also new rubber extension so as to eliminate possible leak in rubber material or leak at rubber/tube joint

Charles

 

[SG]

All the fuel "pick-up" tubes I've ever seen are copper or some other metal?

 

[Capt jgw]

I would suspect a weak fuel pump too. With the tank full the weight of the fuel helps the pump pull the fuel out. As the level drops and that weight reduces, the pump can't do it anymore.

 

[seadaddler]

I would think easy to make pickup tube longer a little or even better a new rubber tube a few inches longer and if still doing it try a new pump.
Nick

 

[Jwhy]

It's the fuel pump. I tested it today in the quiet of the marina and the pump didn't put out any fuel.

Thanks to all for the input.