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KStepman · 27-06-2013, 09:55

I am having an unusual problem with my Yanmar 3YM30 Diesel.

The Engine developed an unusual roughness on a cold start.

It was time for service, so I changed both the primary (Raycor) and secondary fuel filters, and the engine air filter. This helped, but did not fully eliminate the problem.

Currently, when I cold start the engine it initially starts up smoothly, but within 15 seconds it begins to shudder, as if missing in one cylinder; 15 seconds later the shudder settles down to alternating between smoothness and roughness once per second.

The belts are new, and properly tensioned. The impeller was changed based on time, not wear. The oil and filter was recently changed. The coolant is correct. There was no water in the fuel. I have allowed the engine to idle for some time, with no change. I have slowly brought the engine up to full speed while in neutral, with no change.
The engine tach reads 850 rpm at idle.

Any suggestions.

MARINE ENGINNER · 27-06-2013, 10:18

dear kstepman most common is air in the fuel system check your connections , and if you have any copper washer seal in your system change it but don't overtighten

if the problem remains try to bypass your tank with an external canister in order to check if you have any problem at the tank suction line

how old is the engine ?

KStepman · 27-06-2013, 10:46

Good ideas. Thanks.

scoobert · 27-06-2013, 10:46

yes. what are the hours?
air in fuel sounds correct. but if the hours are over 3000-5000 then i can tell you other issues.

KStepman · 27-06-2013, 11:31

Quote:

Originally Posted by scoobert

yes. what are the hours?
air in fuel sounds correct. but if the hours are over 3000-5000 then i can tell you other issues.

The engine is 8 years old. The hour gauge on the tach does not work, I estimate it has under 300 hours.

Sailmonkey · 27-06-2013, 11:59

I had a similar shudder on my 3 cyl kubota. Worse at idle, barely detectable at speed. I finally tightened the packing nut on the fuel shut off valve. Its harder to operate now, but the shuddering is gone.

KStepman · 27-06-2013, 12:32

Quote:

Originally Posted by Sailmonkey

I had a similar shudder on my 3 cyl kubota. Worse at idle, barely detectable at speed. I finally tightened the packing nut on the fuel shut off valve. Its harder to operate now, but the shuddering is gone.

Interesting. Hmmm.

DeborahLee · 27-06-2013, 12:41

If you think its missing on one cylinder try lifting the compression release levers one at a time. If you don't get a change on one maybe a bad injector.