Engine fuel mystery

[Caer Urfa]

Last year removed ALL the existing microbore copper tubing and existing filter and removed tanks to clean.
Fitted a complete new Diesel fuel system, 'ALL' new valves, 8mm & 6.5 mm approved rubber pipework, Pre-filters, none return valve etc everything, also cleaned out tanks.
Each Tek Tank now has it's own filter system
I can run off either tank, or both tanks, but usualy run off one tank at a time
Engine 27hp Isuzu
Problem: After say 8 hrs running at 2000rpm engine just shuts down.
Bleed engine and it will run another 8hrs!
We suspect somehow 'engine is slowly sucking in air' and builds up BUT FROM WHERE?.
Have checked most things three times, everything is tight, diesel is clean and from reliable source.
Any suggestions to next move appreciated ????

 

[dukes4monny]

I'm no expert, and I don't know that engine, but the questions that spring to mind are:

Does the problem occur when using either tank?
Are both of the tanks vented to atmosphere?
Once the engine has stopped, have you tried opening the fuel filler cap and is there an inrush of air?

 

[Caer Urfa]

I'm no expert, and I don't know that engine, but the questions that spring to mind are:

Does the problem occur when using either tank? YES
Are both of the tanks vented to atmosphere? YES
Once the engine has stopped, have you tried opening the fuel filler cap and is there an inrush of air? NO not opened fuel caps

Answer as above if it gives any clues

 

[Cliveshep]

Your air leak is in the "common" section of pipework/fittings, i.e. from changeover valve to filters/pump/injector pump. I personally would question the use of rubber hose with worm-drive clips as shown in your photograph, perhaps copper tube/fittings might be more serviceable. You should check all connections, filter '0' rings, and the things most people ignore, those little fibre washers on bleed screws.

 

[dukes4monny]

Do both of the tanks share a common vent and have you confirmed that this is definately clear?

Many years ago I worked on a small fishing boat which had two new diesels fitted and the tanks repositioned. The first sea trial went well until one engine gradually ground to a halt.......I bled this through and it ran fine again for some time.......then the same thing happened again.
When I opened the fuel filler it went with a 'woosh' of air drawn in........I subsequently found that when the boatyard refitted the tanks they had 'blocked' the common vent......

Does your setup have / require a return pipe? If it does, I assume that you have this switched so that it returns to the tank currently in use?

 

[saxonpirate]

Well, let me first congratulate you on a very neat installation, I like your attention to detail. I'm not sure I agree with Cliveshep on the use of rubber fuel hose/clips as I have used this setup on my own boats without any problems. Ok, a couple of questions...

1. When you bleed the system are you getting a substantial amount of air?
2. Is there a bleed screw on the actual injection pump and if so have you bled it?
3. Does the engine "hunt" at all at certain revs?
4. What sort of injector leak off system does your engine have, back to pump or tank?
5. Silliest question of all....has this problem only started since renewing your piping etc?

It's only a hunch, but I remember working on an John Deere engine many years ago that had exactly the same symptoms. The engine was working hard on a large earthmover and would die after a few hours. The problem in the end turned out to be a blocked leak off back to the tank. This was causing the low pressure side of the injection pump to pressurise and slowly restrict the flow in the pump. Whilst I think this is unlikely in your case it's something that can and does happen.

 

[Caer Urfa]

well, let me first congratulate you on a very neat installation, i like your attention to detail. I'm not sure i agree with cliveshep on the use of rubber fuel hose/clips as i have used this setup on my own boats without any problems. Ok, a couple of questions...

1. When you bleed the system are you getting a substantial amount of air?
I can bleed system in about 10 seconds,ie bubbles come out for say 6 pumps of the injector pump then back to normal.
2. Is there a bleed screw on the actual injection pump and if so have you bled it? No, on the side of the engine
3. Does the engine "hunt" at all at certain revs?no, engine runs fine until it just dies in about 30 seconds, if i bleed it as it is dying it just goes back to normal and will run for another 8 hours!
4. What sort of injector leak off system does your engine have, back to pump or tank?
The return system can be switched over so fuel retuirns back to the operating tank, i also fitted a none return valve.
5. Silliest question of all....has this problem only started since renewing your piping etc?
Problem has only been since renewing everything

it's only a hunch, but i remember working on an john deere engine many years ago that had exactly the same symptoms. The engine was working hard on a large earthmover and would die after a few hours. The problem in the end turned out to be a blocked leak off back to the tank. This was causing the low pressure side of the injection pump to pressurise and slowly restrict the flow in the pump. Whilst i think this is unlikely in your case it's something that can and does happen.

many thanks for your interest

 

[Caer Urfa]

Do both of the tanks share a common vent and have you confirmed that this is definately clear?

Many years ago I worked on a small fishing boat which had two new diesels fitted and the tanks repositioned. The first sea trial went well until one engine gradually ground to a halt.......I bled this through and it ran fine again for some time.......then the same thing happened again.
When I opened the fuel filler it went with a 'woosh' of air drawn in........I subsequently found that when the boatyard refitted the tanks they had 'blocked' the common vent......

Does your setup have / require a return pipe? If it does, I assume that you have this switched so that it returns to the tank currently in use?

Each tank has its own vent,Yes you are right,on the fuel return I can switch the return back to whichever tank I want, usualy the tank I am running off
many thanks for you help.

 

[willie4646]

By the look of your jubilee clips they are the wrong size (to big ) there is to much of a tail sticking out. I would suggest renewing with smaller ones or better still use "0'' crimps.
Willie

 

[Caer Urfa]

By the look of your jubilee clips they are the wrong size (to big ) there is to much of a tail sticking out. I would suggest renewing with smaller ones or better still use "0'' crimps.
Willie

The clips are the 'right size' for the piping, and all have been tightened and re-checked, thats why the post as I suspect something else is the cause as others are starting to suggest.
Thanks

 

[mikewade]

I had exactly the same problem bringing my boat back from the Canaries in June. It followed a complete service by a marine engineer in Las Palmas.
It turned out to be the copper washers on the fuel pipe to pump which were very old and had been reused. We heated them and quenched until we arrived in Azores at which point I replaced everyone of them on all junctions and hey presto, no further problems.

 

[scottie]

what has been added to the original fuel system
can you bypass the change over /filter system fo a test run
have you taken a heater fuel supply of the line it should come direct from the tank as it can cause the problem you are getting

 

[jason -and the arguenauts]

once found myself with a similar situation. tried the obvious of wrapping the outside of each join in that self amalgamating tape. didnt help with the problem but did prove that it wasnt the joints. turned out to be the lucas/cav filter which several engineers have pointed out wasnt designed to be on the suction side of the system but between pump and engine. that argumnent stikes me as an excuse for poor quality butstripping and re-assembling the filter with new washers did the trick.

 

[Caer Urfa]

what has been added to the original fuel system
can you bypass the change over /filter system fo a test run
have you taken a heater fuel supply of the line it should come direct from the tank as it can cause the problem you are getting

Hello Scottie
The original fuel system has been replaced with all new pipework etc and each tank now has its own pre-filter filter and 'all fuel returns' through a secondry filter, previously both tanks had only one filter for the whole system so if one tank went down I was dead in the water.
No my heating is a Taylors Paraffin system
Are you suggesting by 'By-Pasing' the change over valve (also new) it may be the valve??
Thanks for you interest any other suggestion greatfully recieved

 

[Caer Urfa]

once found myself with a similar situation. tried the obvious of wrapping the outside of each join in that self amalgamating tape. didnt help with the problem but did prove that it wasnt the joints. turned out to be the lucas/cav filter which several engineers have pointed out wasnt designed to be on the suction side of the system but between pump and engine. that argumnent stikes me as an excuse for poor quality butstripping and re-assembling the filter with new washers did the trick.

Hello Jason
Are you suggesting that both new filters may have a washer problem?? OR
are you suggesting that the filters are not in the right position?, surely I want to filter after the tanks and before the fuel goes into the pump??
Don't forget the system works fine for up to 8 hrs, hence we think we are sucking in air over a period of time, but from where??
Thanks for your interest

 

[ianat182]

You mention a non-return valve being installed;where exactly,and why. Could it have been installed wrongly and instead of venting, pressurising .
I cannot read the text clearly on one of the fuel cocks but it is in the 'off' position.
I agree it is a neat installation,but I too would prefer copper pipes for fuel.
After 8 hours running I suppose heat/cooling isn't the cause?

ianat182

 

[jason -and the arguenauts]

You're using the filters in the same way as the rest of us boaters. The issue about the design of the Lucas / CAV filter is that they were designed to be under pressure not suction and arent very good under suction. They were mass produced for truck engines.

It could be that both of them leak a little because you have assembled both in the same way. Unlikely but possible.

But as I indicated, first thing to do is to seal off the outside of every join between tank and pump. After the lift pump any leakage would be of diesel into the boat.

You could also have pin hole perforation of the copper pipe.

 

[Caer Urfa]

You mention a non-return valve being installed;where exactly,and why. Could it have been installed wrongly and instead of venting, pressurising .
I cannot read the text clearly on one of the fuel cocks but it is in the 'off' position.
I agree it is a neat installation,but I too would prefer copper pipes for fuel.
After 8 hours running I suppose heat/cooling isn't the cause?

ianat182

Hi Ian
The none return valve was fitted as another elimination possibility,incase we were having problems with backflow, it is fitted on the 'fuel return' from the engine to the secondry filter and we checked it is the right way round,we had the problem before we fitted it! we were just trying to eliminate another possibility.
I can shut everything 'OFF' for mainternance after the pre-filters, or I can select which tank I want the 'return fuel' to go to, but normaly the tank I am useing.
We do not appear to have overheating problems
Thanks

 

[Bilgediver]

We suspect somehow 'engine is slowly sucking in air' and builds up BUT FROM WHERE?.
Have checked most things three times, everything is tight, diesel is clean and from reliable source.
Any suggestions to next move appreciated ????

You got it in one.


suspect your problems are the jubilee clips which are not really the best thing . Take your hose assemblies to a diesel shop or hose specialist or preferably put back the copper pipe .

The only satisfactory fitings are the crimp ones as jubilee clips do not apply good all round compression on the small nipples.

The air is builing up in the primary filters out of sight.

There are correct clips available for fuel hoses which may require a special tool.

If you coud pressurise the system from th tank end you will soon fnd the leak.

 

[Caer Urfa]

You got it in one.
If you coud pressurise the system from th tank end you will soon fnd the leak.

Like most boats the tanks are a pain in the A--- to get at due to access.
How would you recommend pressuring the system to find a leak?
PS: There are no visable signs of any leaks.
Thanks for your interest