Fuel lift pump Yanmar 3 GM30

[Rigger]

Hi. The lift pump on my engine doesn't seem up to priming the primary fuel filter (which unfortunately is fitted higher than the fuel tank) , and my only way round this is currently to suck the diesel through and end up with a mouthful ! I am planning to fit a more powerful bulb type pump (as per outboard motor tanks) between the primary filter and the lift pump. If I did this am I likely to damage the engine lift pump by blowing air and fuel through it? Also,does the lift pump actually function when the engine is running ,or is it for bleeding purposes only. Thanks for any replies,Jim

 

[Bat21]

The lift pump supplies fuel to the injector pump, ideally, the primary filter should be the highest point in the fuel system but at or below the height of the bottom of the tank.
The low pressure side relies upon the head of fuel, the lift pump pumps fuel to the injector pump.

The lift pump does work whilst the engine is running and is powered by the camshaft.

You may find that if you turn the engine over so that the cam lobe is not driving the pump you will get a better throw on the lever and consequently increased fuel flow whilst bleeding the system.

 

[Rigger]

Yes I've tried the lever with various positions of the cam shaft, it just doesn't seem to have the suction. Perhaps the diaphragm is knackered. I have heard of others with the same problem who have fitted the extra manual pump, hence the query.

 

[aztec8484]

I use the brass oil suction pump that you get with a volvo. it sucks the fuel through the primary filter easily.
I am having trouble with my pump as well. I just cleaned the primary filter and pulled through the fuel to the lift pump, but now cannot get the pump to deliver fuel through to the fine filter. I have even tried turning over engine on starter motor but now joy.
I am wondering if there is a prblem with the pump and what it could be. The engine was running fine before I started what I consider to be a routine task!

 

[srp]

I bought a priming pump from www.asap-supplies.com - cat number 302066. You may need a couple of banjo bolts and some copper washers to go with it. It bolts onto the primary fuel filter.

 

[Rigger]

That looks the business! Unfortunately ASAP dont have in stock. Do you just pump right through the existing lift pump?

 

[VicS]

Perhaps the diaphragm is knackered

if the diaphragm is knackered (holed) you will get diesel into the lub oil sump as like as not.

It is more likely that one of its valves is not seating properly.

If the lift pump is not pumping I think you will run into problems with the injector pump losing its prime.

A rubber bulb is fine to aid bleeding, my car has one, but it will not replace the lift pump when the engine is operating.

 

[mikehibb]

if the diaphragm is knackered (holed) you will get diesel into the lub oil sump as like as not.

It is more likely that one of its valves is not seating properly.

If the lift pump is not pumping I think you will run into problems with the injector pump losing its prime.

A rubber bulb is fine to aid bleeding, my car has one, but it will not replace the lift pump when the engine is operating.

What Vic said sound about right, we are having a simialr problem at the moment. HP pump losing its prime. If you have a bad valve on the LP system it can drain down.

Today we checked replaced the the HP bleed screw and seal etc, that now looks OK, so can only be the LP valve left to cause a problem. No fuel leaks anywhere so must be internal drain down.

 

[Leighb]

The lift pump supplies fuel to the injector pump, ideally, the primary filter should be the highest point in the fuel system but at or below the height of the bottom of the tank.
The low pressure side relies upon the head of fuel, the lift pump pumps fuel to the injector pump.

How can the primary filter be the highest point and also be at or below the bottom of the tank? The two requirements seem to be contradictory?

In my boat the fuel tank is below the cabin sole so the bottom of the tank is only a couple of inches above the bilge, it would be impossible to install a primary filter below that !

Can anyone clarify please?

 

[VicS]

The workshop manual describes the procedure for testing the lift pump.
Basically by cranking the engine with the bleed screw on the fuel filter open. If the pump is working fuel will flow from the bleed screw. If it does not then remove the pump discharge pipe and again crank the engine (being prepared to catch any fuel expelled)
If fuel still doe not flow from the pump replace it! There are no internal parts available !