Lift pump problem diagnosis?

[dgadee]

On a vetus m3.10 I have a mechanical fuel lift pump (with a filter inside it). Image attached.

I have problems with getting high revs and there is some hunting at medium revs. My conclusion (which may be wrong) is fuel starvation. I have looked at all the connections and think everything is air tight and the tank vent is free etc. How would I know if the mechanical fuel pump was working but not able to produce enough fuel? I don't want to replace something which is working.

My thought is temporarily replace the mechanical lift pump with an electric one (which I think I have in the garage somewhere). Or sort out a temporary gravity feed. Both seem to involve work. Is there any other way?

 

[pvb]

Have you taken it apart and checked inside it? You need to check the filter and examine the diaphragm and valves. You could try an electric pump.

 

[dgadee]

Just looked at the internal filter. No blockage. Not keen on taking it apart until I know it's bust (and doing a trip over the next couple of days). I have the electric pump so will take it on board and give that a try.

 

[yoda]

Check there is no blockage in any of the supply pipework, blowing back through with an air pump should do the trick. I had similar issues a few weeks ago and found the pickup pipe in the tank was blocked (despite an annual clean of the tank).

Yoda

 

[dgadee]

Check there is no blockage in any of the supply pipework, blowing back through with an air pump should do the trick. I had similar issues a few weeks ago and found the pickup pipe in the tank was blocked (despite an annual clean of the tank).

Yoda

Yes, blown through all the pipes included the return to the tank.

 

[david_bagshaw]

If fitted under and behind the seawater pump, they have a nasty habit of corroding where the lid goes around the filter, along with the diaphragm going baggy, and not delivering the required flow. If the engine is on a generator, later models were fitted with an electric pump, due to ozone causing the diaphragm to fail. I doubt a gravity feed would be sufficient, along with not producing a cooling flow through the pump,

 

[lw395]

Temporarily fit a pressure gauge?
One way to do this is to swap a bleed screw for a nipple.

This does beg the question of what constitutes an acceptable pressure....

 

[dgadee]

If fitted under and behind the seawater pump, they have a nasty habit of corroding where the lid goes around the filter, along with the diaphragm going baggy, and not delivering the required flow. If the engine is on a generator, later models were fitted with an electric pump, due to ozone causing the diaphragm to fail. I doubt a gravity feed would be sufficient, along with not producing a cooling flow through the pump,

Yes - there was a leak and seawater dropped right onto the pump. I don't think, though, that corrosion has let air in. I'll have another look.

 

[dgadee]

Problem seems to have sorted itself without having to look at pump, so presume the pump is ok and that there was a blockage I must have been able to clear. Tank probably needs a good clean out - a few years since it was last done.

 

[pvb]

Problem seems to have sorted itself without having to look at pump, so presume the pump is ok and that there was a blockage I must have been able to clear. Tank probably needs a good clean out - a few years since it was last done.

Don't go out in bumpy seas until you've cleaned it out!

 

[yoda]

Don't go out in bumpy seas until you've cleaned it out!

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