Small Yanmar with a leak… how to fix, if even temporary?

[PetePetePete]

Originally Posted by Wotname

I'm 99.9% sure that is the high pressure injector fuel pipe rather than a return line.

Also... if it was a supply line, wouldn't performance have been impacted?

[skipperpete]

Originally Posted by PetePetePete

Also... if it was a supply line, wouldn't performance have been impacted?

A perfect vacuum is minus 14.7 psi, vac testing an hp injection line with a weep so small that it’s not affecting the performance much (or yet) is unlikely to provide any useful information, this is a miniscule leak that LOOKS like it might be the injector pipe because in your photo’s that’s the area wet with fuel.... the return line is on the other side of the engine and shows no obvious signs of leakage BUT because it’s an air cooled engine the leak could be anywhere and simply blown to another area because of the cooling airflow...... it could also be a fire hazard, the first part of the mixer elbow is un cooled and not insulated, fuel getting on the hot section is quite risky.

[PetePetePete]

Originally Posted by skipperpete

A perfect vacuum is minus 14.7 psi, vac testing an hp injection line with a weep so small that it’s not affecting the performance much (or yet) is unlikely to provide any useful information, this is a miniscule leak that LOOKS like it might be the injector pipe because in your photo’s that’s the area wet with fuel.... the return line is on the other side of the engine and shows no obvious signs of leakage BUT because it’s an air cooled engine the leak could be anywhere and simply blown to another area because of the cooling airflow...... it could also be a fire hazard, the first part of the mixer elbow is un cooled and not insulated, fuel getting on the hot section is quite risky.

Thanks.
I'm well aware of the danger of the fuel on the mixer elbow.

The focus here is to determine where the leak(s) is located from.

I understand that the vac is very limited, however, a leak is a leak, if there's a leak with such a small volume in that tube -- I'd have to guess you'd see it.

[skipperpete]

Better to hook it up to an air supply , maybe 120-140 psi , block the open end and put er into a tray of water, logically you should see bubbles if there’s a crack in that hp pipe. I’m not clear about how you would “see” a vacuum leak, how would you conduct that test?

[PetePetePete]

Originally Posted by skipperpete

Better to hook it up to an air supply , maybe 120-140 psi , block the open end and put er into a tray of water, logically you should see bubbles if there’s a crack in that hp pipe. I’m not clear about how you would “see” a vacuum leak, how would you conduct that test?

The mighty vac has a gauge where you can see if there's a drop.

[Wotname]

It is really difficult to be precise and accurate when trouble shooting remotely with limited information and with only a couple of pictures to aid you.

Recapping - small diesel leak with accumulating over time apparently from a steel (injector?) pipe. I have attached the best picture which was provided by the OP in the first post. Accumulated fuel is visible in the surrounding area.

Going back to first principles - that is a heavy walled injector pipe which operates at 2,500 psi and pulses fuel at half the the engine rpm.

1. Any significant crack in the pipe would drop the pressure below the injector pop pressure and cause engine to stop.

2. Any extremely small failure in the pipe would not leak liquid fuel, it would be atomised diesel vapour and would most likely cause a drop in engine performance.

I have never seen fault #2 but I suppose it is possible. I would expect such a fault would deteriorate rather rapidly to become #1.

My best guess is there a very small fuel leak elsewhere and as suggested by Skippepete upthread, the air cooling is blowing the fuel around and collecting in the blue circled area.

If the engine is running and if the injector pipe is leaking (#2), then it is only leaking once the pressure is exceeding the pop pressure i.e >2000psi. In order to test this, you will need a source of pressure around this figure. However you could clean the pipe, start the engine and spray a soapy water mixture along the pipe. Any leak will be vapour and cause bubbles to form.

This remains my best guess, it isn't gospel

[PetePetePete]

Originally Posted by Wotname

It is really difficult to be precise and accurate when trouble shooting remotely with limited information and with only a couple of pictures to aid you.

Recapping - small diesel leak with accumulating over time apparently from a steel (injector?) pipe. I have attached the best picture which was provided by the OP in the first post. Accumulated fuel is visible in the surrounding area.

Going back to first principles - that is a heavy walled injector pipe which operates at 2,500 psi and pulses fuel at half the the engine rpm.

1. Any significant crack in the pipe would drop the pressure below the injector pop pressure and cause engine to stop.

2. Any extremely small failure in the pipe would not leak liquid fuel, it would be atomised diesel vapour and would most likely cause a drop in engine performance.

I have never seen fault #2 but I suppose it is possible. I would expect such a fault would deteriorate rather rapidly to become #1.

My best guess is there a very small fuel leak elsewhere and as suggested by Skippepete upthread, the air cooling is blowing the fuel around and collecting in the blue circled area.

If the engine is running and if the injector pipe is leaking (#2), then it is only leaking once the pressure is exceeding the pop pressure i.e >2000psi. In order to test this, you will need a source of pressure around this figure. However you could clean the pipe, start the engine and spray a soapy water mixture along the pipe. Any leak will be vapour and cause bubbles to form.

This remains my best guess, it isn't gospel

Wowza!!! That's a FANASTIC reply. Ok! First, much appreciated. I'm going to dig into this son of a gun and report back.

Thank you again!!
Pete

[GordMay]

Originally Posted by Wotname

...
2. Any extremely small failure in the pipe would not leak liquid fuel, it would be atomised diesel vapour and would most likely cause a drop in engine performance...

Won’t high pressure atomized fuel vapours condense back into a liquid state, when the pressure is relived, at the leak?

[Wotname]

Originally Posted by GordMay

Won’t high pressure atomized fuel vapours condense back into a liquid state, when the pressure is relived, at the leak?

It will certainly condense back to liquid somewhere but I could not speculate exactly where that would occur. It may not even be vaporised, rather it may just be atomised liquid. This is assuming it is even possible for such a fine leak to occur without affecting the engine operation.

Lots of interesting stuff about atomised fuel here - https://www.sciencedirect.com/topics...ition%2C%20and

A couple of extracts - In the diesel engine, the jet engine, and kerosene combustion, liquid fuel is sprayed into the combustion chamber with air, and the liquid is not totally vaporized before ignition. Therefore, in drop combustion there are flames around the liquid drops that shrink as the reaction proceeds. This and wood and coal combustion are examples of the shrinking sphere problem of Chapter 17.
We note finally that for most of these processes no one knows their kinetics.

and
The process of liquid fuel combustion is schematically shown in Fig. 4. First, the liquid fuel is atomized by a spray nozzle to generate fine droplets. Then, in the high temperature environment of the combustor, those droplets start to vaporize. Finally, once the temperature is sufficiently high, fuel vapor is autoignited and combusted.

[Compass790]

I'm with Wotname & skipperpete, it is the high pressure fuel injection line & it must be replaced asap. Pulses are hard on steel & if its leaking now it isnt going to fix itself.

I say its the injector fuel delivery pipe as I can see it in one of your pics. I'm actually surprised it can still run.


If you want a temp fix you COULD try welding a sleeve over the leak. I wouldnt rely on it to last as vibration & pulses would cause it to crack. I would try it as I like to experiment but only for emergency repair if no replacement available

[Compass790]

The best way to test it would be to use an injector pop tester, any diesel injection shop has them but if you can see its leaking or spraying from the pipe no need to test as you know its toast.
Are you sure its not leaking from the nut that secures that pipe to the injector?

[Compass790]

Need to clarify what I said:
The pictured pipe is definitely the high pressure fuel line to the injector. If thats the pipe thats leaking it must be replaced.

But its more likely the leak is coming from somewhere else as Wotname & skipperpete suggest.
I think Wotnames explanation about that high pressure fuel line is spot on.

I'll be interested to hear what you discover petepetepete