Yanmar 3GM30 Runaway

[dmksails]

Attempted to start my 3GM30F today and on startup, it max'ed out the the RPMS and would not shut down - neither the throttle or the shutdown had any affect. The engine was last started about 3 weeks ago with no issues. All control cables are moving with no issues or binding. Oil, fuel and coolant all look normal. I has to stop the engine by using the compression levers.

I'm told that this could be from the control rack sticking. Can anyone tell me how to check this?

[AA3JY]

Procedure to check your fuel control rack is in the Service Manual p3-22. The Yanmar Owners group where you first asked this question has the pdf Work Shop manual in their ref. library if you don’t carry one on board

[grantmc]

Wow dmksails that must have been very frightening. Lucky you had the sense and composure to use the compression levers and that it worked.

I've only ever seen a runaway diesel once. It was a very small truck in our big work yard and the engine had been overfilled with oil. (So we assumed oil was being forced in to the combustion chambers.) And it all happened so quickly once switched on, and so loud and alarming, the driver just jumped out and ran yelling a warning. A couple of us in the vicinity didn't need to be told twice. The engine only ran for perhaps 30 seconds blowing white smoke before it blew. It was quite amazing.

Later that day people suggested someone should have flipped the bonnet and put a rag over the air intake, yeah right. The engine was screaming.

I can't imagine that scenario on a boat. I hope I never share your experience and you find a workable solution to the issue. Please dmksails do let us have a follow up.