Help w/ Yanmar 3JH3 Power Drop-Off Mystery

[Britishsea]

I went down to the boat tonight to try to run a jerry connected directly to the fuel filter on the engine, but realized when i got down there that when bypassing the lift pump, there is no way to bleed and prime the hose coming from the jerry can.

Is there a trick here? Will turning the engine over ( with the raw water sea cock off) cause suction on the line with the lift pump bypassed?

Just as an FYI: attached are pics of air in the return line with engine at idle (might be hard to spot the air).

Also a pic of the high pressure fuel pump housing.




Fuel Pump.jpg Views: 63 Size: 410.4 KB ID: 246861" style="margin: 2px" />

[donradcliffe]

You must have missed post #5.

[Wotname]

Originally Posted by Britishsea

I went down to the boat tonight to try to run a jerry connected directly to the fuel filter on the engine, but realized when i got down there that when bypassing the lift pump, there is no way to bleed and prime the hose coming from the jerry can.

Is there a trick here? Will turning the engine over ( with the raw water sea cock off) cause suction on the line with the lift pump bypassed?

Just as an FYI: attached are pics of air in the return line with engine at idle (might be hard to spot the air).

Also a pic of the high pressure fuel pump housing.


Attachment 246860

Attachment 246861

No trick, attach hose to inlet of fuel filter.
Put Jerry can in cockpit a lot or so above the filter.
Fill hose with fuel using a funnel.
Jam the hose into the jerry can.
Loosen the outlet banjo bolt of the fuel filter.
Gravity will siphon fuel though the hose and filter.
Tighten the outlet of the fuel filter once all is expelled in the hose and filter.
Repeat at the inlet to the injection pump. The injection pump may have a bleed screw at it's inlet but if not, just open the banjo bolt.

The new fuel supply (jerry can and hose) is now bleed though to the inlet of the injection pump.

[Wotname]

Originally Posted by donradcliffe

You must have missed post #5.

Yep, the squeeze bulb makes it easier, faster and cleaner but if no squeeze bulb, then Britishsea can use gravity to do the job.

[Britishsea]

Originally Posted by donradcliffe

You must have missed post #5.

Good point - a squeeze bulb will work perfectly for this. In my defence, post #5 was about testing for obstructions/restrictions in the fuel line....

I used to have a squeeze bulb permanently attached in front of my Racor filter in my first boat (C&C30). It never failed and was very handy for changing out filters.....

[donradcliffe]

Post #5 was about using the squeeze bulb to check for restrictions AND the clear plastic tubing to determine the source of air bubbles. The last time I used it, the racor filter had a corroded sealing surface that was the source of the bubbles.

[LittleWing77]

Originally Posted by donradcliffe

The last time I used it, the racor filter had a corroded sealing surface that was the source of the bubbles.

I'm learning a lot from this thread - Thanks everyone!

Related to Donrad's comment above:
There was another thread this past year where the air in the fuel system was caused by an almost-invisible crack in the fuel filter housing where the bleed screw tightened. Not the cause of BritishSea's problem, of course, which seems to be heat-triggered.

Just thought I'd toss in that aside, as sometimes it's a weird, unfathomable contributor that ends up being the culprit.

Good luck, BritishSea and Fair Winds All,
LittleWing77

[Britishsea]

Originally Posted by donradcliffe

Post #5 was about using the squeeze bulb to check for restrictions AND the clear plastic tubing to determine the source of air bubbles. The last time I used it, the racor filter had a corroded sealing surface that was the source of the bubbles.

Thxs Donradcliffe for this. I have a bulb on the way and will do some testing with it. Seems like a good diagnostic tool. Thxs for the tip.

[Britishsea]

Originally Posted by LittleWing77

I'm learning a lot from this thread - Thanks everyone!

Related to Donrad's comment above:
There was another thread this past year where the air in the fuel system was caused by an almost-invisible crack in the fuel filter housing where the bleed screw tightened. Not the cause of BritishSea's problem, of course, which seems to be heat-triggered.

Just thought I'd toss in that aside, as sometimes it's a weird, unfathomable contributor that ends up being the culprit.

Good luck, BritishSea and Fair Winds All,
LittleWing77

Thxs Littlewing for the tip on checking the engine's fuel filter housing. I did inspect the matting surface for the fuel filter and that looked pristine. I was not focused on the fuel filter housing as I had assumed that anything after the lift-pump would under positive pressure, so not likely to permit air to enter the system. Maybe I need to revisit this assumption....

[Britishsea]

Some time has passed and I wanted to circle back on this thread to close the loop.

Thanks to each of you for helping me troubleshoot this engine issue.

I think I found the culprit. I discovered with the assistance of a mechanic that one of the cylinders was occasionally not firing. It tuns out that when I removed the cylinder #2 high pressure fuel line, the female injector nut that it seats into must have also partly backed out - about a 1/8th of a turn. My engine compartment is tiny, so I was undoing these fittings more by feel more than sight. The high pressure fuel pump has a serrated plate secured by a bolt to stop this nut from backing out, but the bolt must have become loose over time or some other factor allowed it not to do its job. This presumably messed up the timing and/or caused cylinder 2 not to always have enough pressure to pop the injector.

I took the boat out today for 40 min sea trial and it seems to be back to normal.

Thank you again to each of you that contributed.

Britsea

[Searles]

Firstly will the engine reach full revs out of gear ,I/E to the governor limit,if so it’s a load problem ,how hot does the gearbox get ,is it water cooled ,check g/box oil level and grade ,something else to check .⚓️⛵️👍