Yanmar diesel lift pump problems?

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ostell

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Helping someone restore a Kingfisher 26 boat. The boat, as bought, had a hand pump in the fuel line. Lots of problems with air in the lines but that's another tale. The engine runs, quite sweetly for an old 2 cylinder Yanmar, but if the engine is stopped for more than, say, 10 minutes it refuses to start because of lack of fuel.

I know that a lot of the fuel line joints need to be checked but the main query is how well will the fuel lift pump in the engine raise fuel? Basically over what sort of height is it able to raise fuel? The fuel tanks in this boat are in the twin keels so there can be quite a height to pull the fuel if the tanks are low.

I have suggested, for test purposes, running the fuel line to a temporary tank on the cabin floor next to the engine and see if that resolves the problem.

Would it be feasible to install a car type fuel pump to resolve any height problems?
 
My generator is a similar engine to yours and the mech fuel pump lifts the fuel by 1metre with no problems. The previous owner had installed a small Facet solid state fuel pump in line to aid bleeding of the system. The pump works well for this purpose. The mech pump is still capable of lifting the fuel through the extra resistance of the electric pump. It might be worth installing the Facet pump as it is a useful feature and it may help you to find the air leak if you can pressurise the system. The main causes I have found in the past have been CAV lucas type filters nipping seals, jubilee clips instead of fuel clips, CAV Lucas filters with missing seals, perished fuel hose.
 
I've just had a look through thge Yanmar GM series manual and it makes no mention of the pump let alone it's capabilities! Indeed there are pages on supplying the engine with water and oil or adjusting the remote cables but very little about how to give some juice... My own gut feeling is that the pump should manage something approaching a 2m head (when new) . The present installation suggests that it used to work OK, but you must make good every joint as failing to start after ten minutes suggests that you're leaking air at a rate that is close to stopping the engine anyway. If the hoses were airtight, I'd personally prefer not to have a hand pump in the system as that is another set of joints which might leak! Others with less than robust systems swear by their outboard style hand pumps. Incidentally, how long have you had the engine run for? It would run for a minute on the fuel you habd pump for starting, but after that it shows that the lift pump is working.

Rob.
 
Lifting by 1 metre should be more than ample for this application.

The engine runs quite happily for 10-15 minutes until stopped. As I said I think the previous owner must have had problems after finding the hand pump in the line. That pump is no longer in the line. I recollect I've seen similar used to drain the oil out of the sump through the dipstick hole.

I've let the new owner look for the problems (It's his first boat, bought of ebay!!) but he seems to be blaming things on the engine itself. Probably a renew of the fuel line right back to the tank(s) would probably be a good place to start. See what happens with the test from a local temporary tank.
 
rob2 said:
If the hoses were airtight, I'd personally prefer not to have a hand pump in the system as that is another set of joints which might leak! Others with less than robust systems swear by their outboard style hand pumps.
Click to expand...

My fuel system is now very robust, but I still like my squeeze-bulb pump. It makes changing the filters an absolute doddle - fit them empty, then pump the fuel in.

Pete
 
I've been experimenting with a Yanmar 4JH 2BE, a cheap Chinese vacuum gauge fitted between lift pump and primary filter and blocked fuel lines. Not through choice I hasten to add.

Anyway, the Yanmar lift pump has to pump fuel through about 6m of pipe and a CAV primary filter. The best vacuum at normal revs is about 3 to 4 ins Hg (about 1.5 to 2 lbs/sq in. The engine stops at 12 ins Hg and there's a noticeable effect at 10 ins Hg.

So if your lift pump is as good as my 23 years old Yanmar lift pump you should be able to lift fuel up the equivalent of about 6 ins Hg over and above the vacuum created by a goodish filter/pipework before you have a noticeable impact on engine running. Not sure of the density of diesel, but it is lighter than water, so if I assume the same as water to give a worst case figure, 8 ins Hg would be equivalent to about 2.5 to 3m (rough mental arithmetic).
 
No short cuts. You need to renew or anneal the copy washers on the pump, watch you don't strip the thread when tightening the unions. Check all the joins and lines between the tank and the pump. There may be debris in the tank.
 
prv said:
My fuel system is now very robust, but I still like my squeeze-bulb pump. It makes changing the filters an absolute doddle - fit them empty, then pump the fuel in.
Click to expand...

Yeah - all shades of grey in beyween. Please excuse my oversimplification, but the outboard style "squeeze the balloon" type of pump is both the best, most effective and reliable type for priming but also has the most annoying failure mode as they tend to soften and the valves stick, blocking the whole fuel line. I guess it means you need to carry a spare...

You can, if the boat design allows, get the best of both worlds by using a gravity feed as far as possible. That way, you bleed everything simply by opening the bleed valve and waiting. The layout I have puts the highest point of the system level with the half-full tank, so if the tank is kept full, I have no fears, but to be offshore with less than half a tank would require a lot of wiggling of the lift pump lever!

Rob.
 
+1 This is a common problem in bigger american boats with Yanmar engines . There are many electric fuel pumps on Ebay, Facet etc which when fitted close to the fuel tank will sort this.
 
The guy is down on the boat today but I couldn't get there first thing. He was convinced that the Injector pump was defective so stripped that down and put it back together again. Still problems and still lots of bubbles when you break the fuel line at the injector pump.

Put a temporary tank on the cabin sole and put the fuel line into that. VOILA !! Engine started, stopped and let rest (bottle of non alcoholic beer) then started again without hesitation and no bubbles when you break the line.

Now we have the problem of the almost runaway engine! because of the meddling with the injector pump.

He now knows that it was not an engine problem but a fuel line problem. The fuel line, probably the original from when the boat was built, is cotton covered rubber.

Plan is to replace the fuel lines to both keel tanks and send that injector pump off for repair at a specialist. Find out within a week or two,
 
The Owners manual is very basic and poorly laid out. The Workshop Manual on the other hand has copious information on the lift pump and evrything else and gives the maximum lift head to be 0.8 M.
You will find the Workshop Manual as a free download and it's pretty essential if you intend to maintain your own Yanmar or understand what the prfofesssionals are telling you.
 
I run a charter boat, I do lots of hours every day. 99 percent of any problems I get with rough running has been air getting in to the fuel lines somewhere. I changed all my copper washers on the filters/ banjos to dowty which seal very well, also rubber fuel lines can be replaced at not much expense, they can split or small tiny pin prick holes letting air in, any damp spot should be treated as a leak. It's an ongoing task, put it on your preventive maintenance schedule.
 
Found out there was a workshop manual yesterday, trying to understand the injector pump.

I'll look for the lift pump specs when I get back there. 0.8m should be OK, unless scraping the bottom of the tank.

I had been trying to convince him that air getting in was a problem, and not the engine. I think that the temp tank and cracking a joint and diesel with no bubbles eventually persuaded him but by this time it was too late and he had taken the injector pump apart.

Just looking at the original fuel pipe suggested that it could be a problem, just had to prove it. I did.

I like those Dowty seals. Will keep that in mind.
 
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