Yanmar YSE12, need help with fuel injector pump

[rewind]

My engine was running fine, at last shutdown, and then would not start at all.

It turns out the injector is not pumping fuel.

Fuel is delivered under gravity feed to the pump, no problem, and when I remove the delivery valve, it drains through the pump without hindrance.

I have taken apart and inspected everything, and cannot see any of the signs of wear described in the original service manual, nor can I see any sign of blockage, however it refuses to pump any fuel at all, when re-assembled.

It was necessary to replace the gasket between the pump body and the piston sleeve that goes inside the engine, and I worry that my hand made gasket is too thick, and might be affecting the stroke.

My engine has two thin metal sheets - shims - between the piston sleeve and the engine block. I presume this is to adjust the fuel pressure.

Before I take it all apart again, is there anyone out there who knows these pumps who could suggest what else I might look for, or how I could set about bench testing the pump, in order to try and work out what the problem is?

 

[rotrax]

My engine was running fine, at last shutdown, and then would not start at all.

It turns out the injector is not pumping fuel.

Fuel is delivered under gravity feed to the pump, no problem, and when I remove the delivery valve, it drains through the pump without hindrance.

I have taken apart and inspected everything, and cannot see any of the signs of wear described in the original service manual, nor can I see any sign of blockage, however it refuses to pump any fuel at all, when re-assembled.

It was necessary to replace the gasket between the pump body and the piston sleeve that goes inside the engine, and I worry that my hand made gasket is too thick, and might be affecting the stroke.

My engine has two thin metal sheets - shims - between the piston sleeve and the engine block. I presume this is to adjust the fuel pressure.

Before I take it all apart again, is there anyone out there who knows these pumps who could suggest what else I might look for, or how I could set about bench testing the pump, in order to try and work out what the problem is?

I was 2nd I/C of the largest Lucas Service depot in the UK for a couple of years back in the early 80's. Our 40 foot narrow boat had a YSE12 in it. Very reliable and economical.

I had Takis our Greek diesel guy overhaul the pump and injector. He was unfamiliar with the specific items, but did a great job.

I suspect you have hit the nail on the head-a thicker gasket might well be the problem.

 

[Spyro]

I think the shims may be to adjust injection timing. A thicker gasket wouldn't be a good idea. From memory I think the throttle needs to be open to get fuel through as having it closed is how those engines are stopped. Is the throttle opening ok and allowing fuel through?
Have you got the manual?
https://www.sailingthanksdad.com/documentation/Yanmar-YSE-YSBServiceManual.pdf
page 17

 

[rewind]

have since rebuilt the pump with a thinner gasket that i am fairly confident matches the original.

yes, i do have the manual (thanks very much to this forum, and that link) and as far as i can see, everything is in good condition, there are no obvious signs of wear, and everything seems to be working.

i have checked the regulator needle valve spacer, and am fairly confident that it is not sticking.

i have "bench tested" the pump by connecting it to the supply, and working the plunger in and out by hand, without the spring. the only way i can persuade it to pump fuel is by unscrewing the delivery valve holder a couple of turns. this slackens the spring, and it will then push fuel through the delivery valve.

to double check this, i put pipe tape on the delivery valve holder threads, and put the pump back into the engine. i was then able to bleed the system ok, but the pump does not appear to be producing enough pressure to get fuel through the injector.

my general diagnosis is that the plunger and barrel are worn out, and i am now in the process of ordering a new set.

what bothers me is that the engine was running fine, about a week before, when i last shut it down - no sign of loss of power or any of the gradual effects i think i should expect from a pump that is slowly wearing out. it just stopped, dead, and refused to pump fuel the next time i tried to start.

as far as i can tell i have re-assembled the pump correctly, using both the service manual diagrams and the exploded views in the parts catalog, and i cannot think what else might be the problem. perhaps i will try without the replacement gasket at all, just in case it helps, but given my manual tests, i am not confident this will make any difference.

the only other thing i can think of is perhaps i should not have added diesel fuel "cleaner" to my tank? the fuel i am running on is probably three to five years old now, although i did add 5 gallons of new fuel to about 12 of old, about a year ago. again, there have been no problems, and everything was running fine, until now.

i think perhaps, for the next test, i will borrow a tank of new clean fuel, and see what difference that makes.

thank you both for your prompt replies, very much appreciated - i am very glad you are here, i would be clueless without this forum - thank you for being here.

 

[blan321]

Very similar to YSE8 in my previous yacht. Dismantled and rebuilt engine. The gasket does control injection timing.
Pump itself is very simple. I wonder if your injector is the issue - if you had a spare or could borrow one, could test for spray in a jar - remember skin penetration of the jet can be lethal!

 

[rewind]

thank you for the warning, i did not know an injector could be dangerous. i pulled mine late last year and had it professionally checked, and it was fine then. of course, that means nothing, as it could have become blocked since. however the pump is definitely not working right - even when i relax the spring in the delivery valve, the fuel it produces is not under any significant pressure. am going to try with new fuel next, as soon as i can get some (takes a while, where i live) and if that does not work, i think i must replace the pump plunger and barrel.

 

[Spyro]

The OP says the injector pump isn't working. If he opened the joint at the injector. Opened the throttle and turned the engine he should be able to prove the pump workin or not. If he got a good flow of diesel I'd then suspect the injector.

 

[Topcat47]

I know it's a different model, but my 1GM10 has no gaskets between the pump body and the engine casing, only the shims. I've had the pump and injector serviced three times over the years, replacing the correct shims, and there's never been a leak between the pump body and the casing

 

[black mercury]

Hi, you seem to have checked everything. Very unusual for pump to stop working like that, they usually go down hill slowly as plunger and barrel wear, except if they seize, which is not your case. Only thing i would try is to test the delivery valve. If it is faulty it could draw air in down through the valve instead of diesel. Mount the pump with delivery valve pointing upwards and put a few drops of diesel down inside the valve until its level with top of threads. Then operate the pump carefully by hand. The diesel should stay level at the top when you pull the plunger on its downward stroke. If the diesel is sucked through the delivery valve it isn't sealing. I also assume that when you are testing the pump by hand you are moving the rack back one way and then the other. One way will be fuel off and the other will be maximum fuel.

 

[rewind]

yes, i can confirm that my YSE12 also has only shims between the complete pump and the engine casing. however, between the pump and the engine is a separate part called the plunger barrel, which serves as a guide for the roller bearing, which rides on the cam, and drives the plunger. between the pump body and the plunger barrel is a gasket, described as "packing" in the original service manual, and the parts catalog.

 

[rewind]

thank you, i will try this, as soon as i get some clean fuel to test with, and i presume by rack you mean the thing yanmar calls a regulator spindle? if so, yes, i have been testing with the valve wide open, and also with the spindle removed completely.

 

[rewind]

to close this thread, i thought is should say what happened.

bought a new injector, installed, same problem.

and then i read the service manual again, and i had missed a step.

in the first bleeding step, it is IMPORTANT to slacken off the outlet ball valve spring holder as far as possible, to first prime the pump properly. tighten again when fully bled, and proceed with the remaining bleeding steps.

this seems to be the step i missed, in the first place.

 

[LittleSister]

Glad you got it sorted in the end.