Engine noise

[Tom and Pat Fudale]

My Cat C9 will start and idle fine for about 15 or twenty seconds, then it will make a clattering noise, somewhat like a spark knock on a gas engine. When it clatters it seems to stumble also but then it will to idle smoothly. I received two different answers from two service managers. One said it was probably a  leaking injector and the other said it was probably air leaking into the fuel system. I might add that only happens on a cold start-up or after the engine has'nt been run fur a few days.I never happens when the engine is hot. Other than that the engine runs fine.

[Gerald Farris]

Tom,
The noise could be caused by either problem. From my experience, the most likely cause is a leaking injector.

Gerald

[Tom and Pat Fudale]

But explain why it would idle for sometimes for even a half a minute for it starts to clatter.  I would think that if the injector was leaking onto the piston, that it would clatter immediately on start-up.

[Gerald Farris]

Tom,
The operating temperature of an injector increases as an engine warms up. Therefore there is a possibility that an injector is malfunctioning at a specific temperature and/or pressure that can only be achieved as the engine warms up from a cold start.

Gerald