Baffling Yanmar 3GM30F Problem/Fault?

[BobnLesley]

We're in the boondocks as ever so in the absence of a local mechanic I'm once again consulting to the experts:
Our engine starts as promptly and sweetly as ever, with no exhaust smoke of any colour/description and no signs of any cooling water getting where it shouldn't be. All remains well when we first engage gear (forward or reverse) in tick-over, but immediately that we increase the revs/load on the engine it sounds and feels as if it's only running on two of the three cylinders. Once it reaches around 1500rpm if you ease the revs back just a touch and then increase them again, it works fine and the problem doesn't reoccur until you start it the next time. To be honest I think the engine's always been this way to a degree and I think the problem's worse when the engine's not been started for a week or two, but I do perceive that it's perhaps getting worse/more noticeable; anybody had the same or got any ideas?

 

[ctva]

Sticky valve or perhaps a blocked injector?

 

[Fr J Hackett]

Governor is sticking

 

[bikedaft]

You can feel the pulse/clikck on each the 3 diesel lines leading to the injectors. Or for the absence of same. Can use the deconpression levers individually (for a short while) to check which of the 3 cyl's is not working when under load.

Governer sounds a good bet tho.

 

[Bilgediver]

One check is with the engine running immediately after start slack off the injector pipe nut on each injector one at a time then retighten. Have kitchen roll handy to catch spillage. Report back if all cylinders responded the same and was fuel spilled from all loos connections. Repeat when under load.

Basically if no, no speed change then that cylinder is taking a holiday if all cylinders give a similar reduction of speed then all ok .

 

[Fr J Hackett]

Why is it fleetingly under certain conditions running on only 2, is it always the same one missing, perhaps, he only said it sounds like? It could be useful to determine if it is missing but the real question is what is causing it. Fuel pump / governor are the obvious culprits and neither likely to be resolved in the boondocks.

 

[bikedaft]

Ps where are you?

Someone has loosened the unions at injector ends on our 3gm30f, and twisted the fuel pipe, so be careful doing that.

(That was why i suggested using decompression levers first, one at a time)

 

[Bilgediver]

Ps where are you?

Someone has loosened the unions at injector ends on our 3gm30f, and twisted the fuel pipe, so be careful doing that.

(That was why i suggested using decompression levers first, one at a time)

Bad practice....... Never decompress when engine is running.... Easiest way to get carbon under valve and initiate leakage. If I undoing the injector nut twists the pipe then sort the problem as it should not.

This is the best way to check individual cylinder performance on a diesel and confirms that fuel is flowing and that cylinder is firing so has fuel and compression.

 

[BobnLesley]

Ps where are you?

Bora Bora, French Polynesia. The nearest Yanmar mechanic's 30M upwind/sea and we've plenty of both this week, or probably easier is 1300M downwind to Tonga.

 

[Fr J Hackett]

Bora Bora, French Polynesia. The nearest Yanmar mechanic's 30M upwind/sea and we've plenty of both this week, or probably easier is 1300M downwind to Tonga.

If it is the governor you need a fuel injection specialist rather than a Yanmar Mechanic.

 

[Biggles Wader]

Bora Bora, French Polynesia. The nearest Yanmar mechanic's 30M upwind/sea and we've plenty of both this week, or probably easier is 1300M downwind to Tonga.

I cant fix your problem but I can recommend a trip to Tonga. Nukualofa is nice and Vavau is quite idyllic. Enjoy!

 

[Bilgediver]

Why is it fleetingly under certain conditions running on only 2, is it always the same one missing, perhaps, he only said it sounds like? It could be useful to determine if it is missing but the real question is what is causing it. Fuel pump / governor are the obvious culprits and neither likely to be resolved in the boondocks.

Doubt if it is a governor problem however it could be a fuel pump delivery valve problem . Do the test I suggested next time the engine misbehaves and tell us the results then we can help isolate the problem. Confirm if there is fuel at all cylinders when the fuel nut is loosened. Confirm that when each nut is loosened the engine appears to loose the same amount of power. If one cylinder indicates no difference then tell us which one.

 

[BobnLesley]

Thanks for the input everyone, so what more do I know:

I tried to make Bilgedivers test of easing the injector-nuts, but didn't really learn much as the problem only lasts for 5-10 seconds, so it's running smoothly before I can get the nuts undone, looked at and then re-tightened.
If it is the governor I do have a spare (secondhand) fuel injector-pump, though I'm reluctant to exchange the one I have on currently as I don't know if it's better or worse than the one currently fitted and understand that it's not really just a bolt-off/bolt-on job and that these pumps need specialist 'tuning' as part of the installation process? I'd perhaps try it if the engine was stopped and wouldn't restart, but I'm reluctant to 'give it a try' on a motor that currently works fine for 99.9% of the time. The engine always picks-up and runs eventually, the misfire only going from 1-10 seconds, my big concern is that whether the engine shake during this short misfire period is screwing-up the transmission.
Some (possible?) light was that whilst trying to make Bilgedivers suggested test, I also as a matter of course bled the fuel supply and think; I stress only 'think', that there might've been the tiniest of air-bubbles come from the top of the mechanical lift pump - definitely none from the bleed bolts on either the secondary filter or injector-pump; could that have caused the problem? It's started/run fine since doing so, but having started/stopped it a dozen times over the last two days, that in itself might be what's giving me temporary respite; as I said originally, the problem's more pronounced when the engine's not been run for a few days/weeks.

 

[Fr J Hackett]

My money is still on the governor or fuel pump and as you say you need a fuel injection specialist so leave well alone until you can find one, he doesn't have to be a Yanmar engine specialist any diesel fuel injection workshop should sort you out best get the spare pump serviced as well whilst you are at it.