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JP3 Fuel Air Leak?


steve.sharratt
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Hi all,

 

This is a continuation of my previous thread.  I thought I would start afresh as the last issue was technically solved.  I went for a 10-day run along the Wey to Guildford and she started fine every time and ran well except the occasional cough. This included a few 36 hour stops.  Got home on Saturday afternoon after good run up the Thames and tried to start her on Tuesday - she wasn’t having it. I have learned to listen for a ‘distinct sound she makes when trying to fire and I just wasn’t hearing it.  This is the same as the previous thread.  Long story short - I disconnected the fuel lines at the injector and hand cranked but didn’t get the eventual squirt of fuel I did last time.  I then (following the JP manual guide for priming) removed each delivery valve holder on the fuel injection pump.  No 1 hesitated and then blew a swag of bubbles before flowing freely. Nos 2 and 3 were less interesting - just slowing began to flow with fuel.  Reconnected and after a few coughs and splutters she fired up.  I did get a large puff of black smoke out of No3 valve cover but she quickly settled.  

 

That’s the story. My question/enquiry is… is it likely an air leak and is there a clever way of tracking to the source?  Also, would the occasional splutter I get be related?  I have a short video but only in MOV and MP4 and neither are accepted.  

 

 

 

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Statement of the bleeding obvious:  You have an air leak before the injection pump.

It must be somewhere that is under suction when the engine is stopped. Air in is a lot more annoying than diesel out, as at least you can see the latter.☹

  Have you tried bleeding the injection pump through the two bleed screws at the top of the pump (about a 5/8 in hexagon, one either end on the side with  the dip stick)?  That should be quicker than taking the delivery valve holders out.

 

Can you pressurise the fuel system,   even temporarily so as to show where the leak is?  A small header tank and a bit of pipe would do, if it can be connected in.

 

N

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If you have the original fuel filter, that is probably the source of the leak - particularly if it is the duplex (double) type.

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6 hours ago, BEngo said:

Statement of the bleeding obvious:  You have an air leak before the injection pump.

It must be somewhere that is under suction when the engine is stopped. Air in is a lot more annoying than diesel out, as at least you can see the latter.☹

  Have you tried bleeding the injection pump through the two bleed screws at the top of the pump (about a 5/8 in hexagon, one either end on the side with  the dip stick)?  That should be quicker than taking the delivery valve holders out.

 

Can you pressurise the fuel system,   even temporarily so as to show where the leak is?  A small header tank and a bit of pipe would do, if it can be connected in.

 

N

I haven’t tried the bleed screw as I followed the manual for Priming the System.  I did see that it mentioned bleeding from (what they call) the closing plug in the trouble shooting section.  I will have a look tomorrow. I do have a large syringe which could work for pressurising the system. I will give it a try and let you know.  

 

Cheers

 

Steve

3 hours ago, BWM said:

If you have the original fuel filter, that is probably the source of the leak - particularly if it is the duplex (double) type.

I don’t have the original filters but it will be worth checking my filter system to make sure all of the bungs and plugs are properly sealed.  Haven’t noticed any leaking from there but then I wasn’t looking!

 

Cheers

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15 hours ago, steve.sharratt said:

I haven’t tried the bleed screw as I followed the manual for Priming the System.  I did see that it mentioned bleeding from (what they call) the closing plug in the trouble shooting section.  I will have a look tomorrow. I do have a large syringe which could work for pressurising the system. I will give it a try and let you know.  

 

Cheers

 

Steve

I don’t have the original filters but it will be worth checking my filter system to make sure all of the bungs and plugs are properly sealed.  Haven’t noticed any leaking from there but then I wasn’t looking!

 

Cheers

The banjo that connects to the end of the pump is also worth a look as they can leak, especially if knocked. It's well worth drying everything off and then running your finger over the underside of the pipework, ect., to pin down the source. 

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22 hours ago, BEngo said:

Can you pressurise the fuel system,   even temporarily so as to show where the leak is?  A small header tank and a bit of pipe would do, if it can be connected in.

 

Does a JP not need a day tank and gravity feed? 

 

If it does, I wonder if the OP has a valve in the feed which is partially (or fully) turned off causing a slight vacuum but only when the engine is running.

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21 minutes ago, MtB said:

 

Does a JP not need a day tank and gravity feed? 

 

If it does, I wonder if the OP has a valve in the feed which is partially (or fully) turned off causing a slight vacuum but only when the engine is running.

Ideally yes but I do know of a couple that have electric fuel pumps fitted….wouldn’t be my choice I must admit. 

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29 minutes ago, BWM said:

The banjo that connects to the end of the pump is also worth a look as they can leak, especially if knocked. It's well worth drying everything off and then running your finger over the underside of the pipework, ect., to pin down the source. 

Interesting as I was just looking at that and I noticed that the flex fuel line coming from the filter to the banjo was very wet (it is U shaped so could be leaking from either end). I have dried it off and will check later but I have some new fuel line so will probably replace it regardless.

27 minutes ago, MtB said:

 

Does a JP not need a day tank and gravity feed? 

 

If it does, I wonder if the OP has a valve in the feed which is partially (or fully) turned off causing a slight vacuum but only when the engine is running.

 

5 minutes ago, frangar said:

Ideally yes but I do know of a couple that have electric fuel pumps fitted….wouldn’t be my choice I must admit. 

I have a gravity-fed day tank (no electric pump). I am paranoid about opening the fuel valve prior to starting and have checked that.  I did wonder whether as the day tank empties the pressure becomes insufficient.  I don’t think that is the problem though as when I bleed the system it has no problems with fuel flow.

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11 minutes ago, steve.sharratt said:

I am paranoid about opening the fuel valve prior to starting and have checked that.

 

You may be opening the valve by turning the handle, but how do you check it really IS fully opening and fuel is flowing?

 

 

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On Bosch clone BPE type pumps the Bosch practice of fitting a very fine gauze filter inside the fuel line  banjo is followed.....and this tiny filter screen is often overlooked in fuel starvation troubleshooting.....and assuming the rubber rings in the fuel filter top havent been replaced since 1950 ,Id check that too,and maybe  replace the rubber rings next filter change instead of tossing them in the toolbox..................to find leaks ,disconnect the fuel pipe at the tank,let the fuel run out of pipe and pump,,paint the whole system with washing up detergent ,and pressurize the whole lot,including the pump,with compressed air ...should be a mass of bubbles at any leak......easily bled after test...bleed at the screws on the pump chamber,dont go loosening high pressure fittings.

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I have now pressure tested the line from the day-tank using a large syringe. I believe there was a good amount of pressure but I got no obvious indication of any leak and strong resistance from the syringe.  The banjos on each end seemed clean so I didn’t touch them. I replaced the fuel line between the filters and the fuel pump (it looked dodgy) and then bled the pump at the closing plug and almost immediately got a very strong flow of fuel (not bad as the pump did drain off a bit of fuel when I replaced the fuel line).  She then started on the first attempt. I am confident it not a starvation issue as she was run quite hard on the Thames for several hours with no problems and any bleeding shows good fuel flow.  

 

I will give the engine a good cleaning tomorrow and let it sit for a few days and then try to start again. 

 

I will keep you posted.

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19 hours ago, steve.sharratt said:

I have now pressure tested the line from the day-tank using a large syringe. I believe there was a good amount of pressure but I got no obvious indication of any leak and strong resistance from the syringe.  The banjos on each end seemed clean so I didn’t touch them. I replaced the fuel line between the filters and the fuel pump (it looked dodgy) and then bled the pump at the closing plug and almost immediately got a very strong flow of fuel (not bad as the pump did drain off a bit of fuel when I replaced the fuel line).  She then started on the first attempt. I am confident it not a starvation issue as she was run quite hard on the Thames for several hours with no problems and any bleeding shows good fuel flow.  

 

I will give the engine a good cleaning tomorrow and let it sit for a few days and then try to start again. 

 

I will keep you posted.

 

I tend to let the engine cool before shutting off the day tank as I found that as the engine cooled there was a vacuum created as the fuel cooled..which seemed to create air type issues....this too was with no visible leaks when the system was left with the valve on the day tank on. Now when boating everyday I dont bother turning the day tank valve off.....that only happens when moored up for longer periods...say 3-4 days.

 

If you have the engine mounted duplex filters then try using the changeover valve on them to see if its just one filter that causes issues.

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10 hours ago, frangar said:

 

I tend to let the engine cool before shutting off the day tank as I found that as the engine cooled there was a vacuum created as the fuel cooled..which seemed to create air type issues....this too was with no visible leaks when the system was left with the valve on the day tank on. Now when boating everyday I dont bother turning the day tank valve off.....that only happens when moored up for longer periods...say 3-4 days.

 

If you have the engine mounted duplex filters then try using the changeover valve on them to see if its just one filter that causes issues.

That’s interesting.  I do tend to turn off the fuel at shutdown - so I don’t forget.  I’ll give it a try!

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14 minutes ago, steve.sharratt said:

That’s interesting.  I do tend to turn off the fuel at shutdown - so I don’t forget.  I’ll give it a try!

 

 

Hmmmm why? 

 

Honestly, what do you think might happen if you left the day tank outlet turned ON? 

 

 

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Interesting fact:

 

When I fitted a chinese diesel heater, for simplicity I nicked the diesel supply from the day tank by tee-ing into the engine supply. Worked fine. One freezing cold day I arrived at the boat and turned the diesel heater ON. After about ten minutes' running it shut down. No fuel! I'd forgotten to turn ON the day tank outlet valve, duh. 

 

Engine would not start. Turned out the heater had sucked the whole of the diesel out of the fuel pump and all the pipes. An hour of fcuking about bleeding all the air out......

 

Point being, the injectors will leak air back in when subjected to negative pressure. 

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Thats an interesting point...... an injector pump will pull enough vacuum to collapse a sheet metal fuel tank if the vent blocks up...

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On 06/05/2022 at 12:04, frangar said:

 

I tend to let the engine cool before shutting off the day tank as I found that as the engine cooled there was a vacuum created as the fuel cooled..which seemed to create air type issues....this too was with no visible leaks when the system was left with the valve on the day tank on. Now when boating everyday I dont bother turning the day tank valve off.....that only happens when moored up for longer periods...say 3-4 days.

 

If you have the engine mounted duplex filters then try using the changeover valve on them to see if its just one filter that causes issues.

Mine is exactly the same. If I turn the fuel shut off  valve from the day tank too soon after a hard run, I have to bleed air from the pump next morning. After a gentle day's running there's no problem.

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19 hours ago, monkeyhanger said:

Mine is exactly the same. If I turn the fuel shut off  valve from the day tank too soon after a hard run, I have to bleed air from the pump next morning. After a gentle day's running there's no problem.

I think that could be the problem.  I will leave the valve alone from now on.

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