Yanmar 3TNA72UJ engine injector pump

[MinniMan]

Hi I hope this is the right place to put this question. I have a John Deere F935 mower and the tractor part has the engine mentioned in the heading of this post.
I replaced all three injectors with new ones as the old ones tested poorly. Engine has 3000 hrs on it. After putting the new injectors in it still runs very rough and sometimes misses on the cylinder nearest the flywheel. I'm calling it number 3.
I loosened the injector line at the injector and of course bubbles poured out. Left it loose for a while with the engine running but they didn't stop appearing. So I tightened up the nut on the injector and loosened the one on the injector pump and still had air bubbles pouring from there. They didn't stop coming even after running for probably 5-10 minutes. If I loosen the nut on either of the other injectors there are no bubbles at all.
I put a clear line on the fuel line from the filter to the injector pump to check for air getting in via the fuel inlet and no sign of bubbles once it was fully bled. So no air getting in that way.
So is it possible that one of the pumps in the injector pump can somehow leak and allow air into only one injector?
The injector pump make and model number is Yanmar 719621-51100 T606 61.
I would appreciate any advice or help I can get on this. Does it need to be rebuilt or replaced with a new injector pump or is there a seal leaking somewhere to allow air into only one injector line?
Thanks very much for any help.

 

[WTW]

Sounds just like my 332 JD with Yanmar diesel as it would always miss on #3 cylinder. I could of
swore it was a injector but was not, rather a fuel restriction in tank pick-up tube causing a low
charge supply pressure to injection pump. Check the supply from transfer pump to injection pump that
it will flow plenty of fuel to injection pump. If not check for restriction in fuel circuit between
transfer pump and tank. Mine was a swollen / restricted pick-up hose in tank DW

 

[504]

I can speak about the pickup lines in the fuel tank coming apart. I have had that problem with an F-932(gas)430 D,318 gas. The F-932 with two tanks takes 10 feet of line to replace all of them,and after doing it twice I only use the clear line from the dealer.

 

[MinniMan]

So if I understand you correctly if there is a restriction in the pickup line in the tank even though the fuel pump, pumps fuel it may not be enough volumn to meet the needs of the injector pump and could lead to it cavitating and somehow getting air into the delivery fitting and then to the injector. Remember I had a clear fuel line on the fuel pump line from the filter and no sign of any air bubbles coming from the pump through the filter to the injector pump. I had this fuel line off with the fuel pump running (electric pump which is new) and it appeared that there was a good flow of fuel out of the fuel line.
Does the body of the injector pump fill with fuel from the fuel pump and filter? I mean the part of the pump housing with the camshaft in it that moves the injector pistons up and down to pump fuel or is it empty and could that be where the air is being picked up by the injector pump piston if it is starving for fuel?

 

[MinniMan]

Just an update on the injector issue. Replaced all three injectors with import ones and its running fine so far. I do plan to replace all the fuel lines and clean and check the screens in the tank this winter. But it should be ok until we are finished with mowing this fall. Thanks to everyone for their help it is greatly appreciated.

 

[Dieseltech]

Make sure NONE of the three injection pump outlets are loose. Use TWO wrenches and remove the injector lines, now torque each outlet to 25 FT/LB and replace the lines. When ANY outlets are not tight the fuel to injector will bypass internally and cause a miss. Another redneck check I do to see if an injector is stuck OPEN, remove all injector lines at injectors and place aside. Now crank engine, there should be NO fuel/air blow backward out the injector inlet. If compression air DOES come out, then injector is stuck open and needs repair.

 

[MinniMan]

Well I ran the rest of the season after replacing the injectors and didn't have an issue so I suspect it was a bad injector. We have fired it up a couple time this winter in the shop to move it around and it fired up immediatly and ran smooth as a 3 cylinder ever does. But thank you everyone for the suggestions. It is always appreciated. Just thought I should give an update on how things turned out.