Yanmar 2GM20 Fuel problem

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croz

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Need a bit of support I guess as Ive spent 2 days working through a problem which have not solved yet as follows:

Boat been in refit for 2.5 years unknown before then
Fuel tank moved from gravity fed to needing fuel lift pump - engine lift pump only
Pump pulls through a CAV Type water separator and CAV fuel filter/separator in line Water separator first and higher than the fuel filter
I have mounted a new push type priming pump on the outlet of the CAV fuel filter before fuel goes down to the engine lift pump
Engine starts really well and runs sweet as you like for around 10 mins under load then dies.
All fuel between hp pump and bottom of CAV fuel filter (ie top of bowl) is used and air now in system
System from fuel filter to hp pump needs re bleeding at this point
I have now pressure tested whole system for 15mins with minimum air drop from 2bar and no indication of air leaks from leak testing spray

Im suspecting the fuel lift pump as it seems relatively ineffective as a system priming pump - ie useless!
Also I think a pinhole or leak in the diaphragm/ fuel lift pump would allow air in from the crankcase and logic seems to suggest it would gather in the fuel filter as this is the first high point.

Am I missing something or just quietly going insane in my own little world!!
 
croz said:
Need a bit of support I guess as Ive spent 2 days working through a problem which have not solved yet as follows:

Boat been in refit for 2.5 years unknown before then
Fuel tank moved from gravity fed to needing fuel lift pump - engine lift pump only
Pump pulls through a CAV Type water separator and CAV fuel filter/separator in line Water separator first and higher than the fuel filter
I have mounted a new push type priming pump on the outlet of the CAV fuel filter before fuel goes down to the engine lift pump
Engine starts really well and runs sweet as you like for around 10 mins under load then dies.
All fuel between hp pump and bottom of CAV fuel filter (ie top of bowl) is used and air now in system
System from fuel filter to hp pump needs re bleeding at this point
I have now pressure tested whole system for 15mins with minimum air drop from 2bar and no indication of air leaks from leak testing spray

Im suspecting the fuel lift pump as it seems relatively ineffective as a system priming pump - ie useless!
Also I think a pinhole or leak in the diaphragm/ fuel lift pump would allow air in from the crankcase and logic seems to suggest it would gather in the fuel filter as this is the first high point.

Am I missing something or just quietly going insane in my own little world!!
Click to expand...
I know a chap with a She 36 with the same problems ;)
 
Effectively yes - fed through the same separator and filter arrangement. Fuel lift pump didnt really have to do any work before I moved the tank. Thats why I suspect that replacing it might solve the problem but there be better brains than I on here... and I need some comfort that chucking £110 or so at it will be the answer
 
croz said:
Effectively yes - fed through the same separator and filter arrangement. Fuel lift pump didnt really have to do any work before I moved the tank. Thats why I suspect that replacing it might solve the problem but there be better brains than I on here... and I need some comfort that chucking £110 or so at it will be the answer
Click to expand...
is the lift pump serviceable ie is a spares kit available
 
Georgio said:
Not really serviceable, had to replace my lift pump on a 2gm earlier this year as it failed. There was a chap on eBay selling yanmar boxed pumps for about £70 delivered which was as cheap as I could find.
Click to expand...

Great Steer Georgio - Thanks :) I think replacement seems the right option
 
croz said:
Need a bit of support I guess as Ive spent 2 days working through a problem which have not solved yet as follows:

Boat been in refit for 2.5 years unknown before then
Fuel tank moved from gravity fed to needing fuel lift pump - engine lift pump only
Pump pulls through a CAV Type water separator and CAV fuel filter/separator in line Water separator first and higher than the fuel filter
I have mounted a new push type priming pump on the outlet of the CAV fuel filter before fuel goes down to the engine lift pump
Engine starts really well and runs sweet as you like for around 10 mins under load then dies.
All fuel between hp pump and bottom of CAV fuel filter (ie top of bowl) is used and air now in system
System from fuel filter to hp pump needs re bleeding at this point
I have now pressure tested whole system for 15mins with minimum air drop from 2bar and no indication of air leaks from leak testing spray

Im suspecting the fuel lift pump as it seems relatively ineffective as a system priming pump - ie useless!
Also I think a pinhole or leak in the diaphragm/ fuel lift pump would allow air in from the crankcase and logic seems to suggest it would gather in the fuel filter as this is the first high point.

Am I missing something or just quietly going insane in my own little world!!
Click to expand...



You have found the classic problem of placing the CAV between the lift pump and a low mounted fuel pump . This has been done to death here and the best solution is to install a small electric/electronic diesel fuel pump close to the tank.

To effectively prime your system you need either to pressurise the fuel tank. I use a length of garden hose and lung power though some here have installed a bulb type pump in the fuel line near the tank.


The CAV needs pressure bleeding to ensure it is filled and there is no air which you cannot see within the filter.
 
Well thank you everyone for the advice. CAV prime pump is fitted on the outlet of the CAV filter and works brilliantly. Fuel lift pump change did nothing other than help me bleed the engine side better - there must have been something wrong with it but not air related. I can prime and bleed the whole system really easily. Takes about 3 mins from dry so no issues there but it seems the CAV prime pump easily overcame the air leak!!

Have progressively isolated the systems today and discovered that all my work has been fine and all joints between tank and engine are sound HOWEVER....... I trusted a tank manufacturer to pressure test the tank (and I would assume the thru tank fittings.....) and it appears that the only place I can be drawing in air is the surface joint as the pick up pipe comes through the top of the tank - either above or below the tank top Im not sure which. I can't check this bit with a pressure test so the tank is now out and I will "have a chat with the manufacturer" in the morning. Brings in the ASSUME bit is to make and Ass of U and Me to mind.....

Im not a fan of the electric lift pump idea as its more to go wrong and shouldn't really be necessary in a well sorted system for a small engine but I guess its horses for courses.

Meantime thank you all for you pointers and between us all I think Ive now isolated the issue so fingers crossed can sort asap
 
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