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Old 07-10-2020, 09:02 AM   #1
Bus Nut
 
Join Date: Jan 2020
Location: Wild Wild West
Posts: 691
Year: 1999
Coachwork: Blue Bird
Chassis: TC RE
Engine: 8.3 Cummins MD3060
Rated Cap: 84
Engine noise on start up

This start up video is after sitting for over 2 weeks. One little puff off black smoke on initial start which isn’t a problem. My question is about the change in tone at the 15 second mark. It’s much more noticeable in person. I don’t know how to describe it. It’s not a change in RPM, or a change in pitch, Moore like a change in the harshness of the diesel sound. I haven’t noticed that it ever goes back to the initial tone until the next start up. Also haven’t shut it off and restarted it immediately to know if it only does it on cold start up. Any ideas?


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Old 07-10-2020, 09:21 AM   #2
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Location: Southern Maine
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Year: 1988
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Chassis: Phantom 40'
Engine: DDECII 6V92T Allison MT647
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Is that the sound of the EGR valve being open? It does have a more 'hollow' sound after 0:15, doesn't it?
Just my guess...
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Old 07-13-2020, 09:39 AM   #3
Bus Nut
 
Join Date: Jan 2020
Location: Wild Wild West
Posts: 691
Year: 1999
Coachwork: Blue Bird
Chassis: TC RE
Engine: 8.3 Cummins MD3060
Rated Cap: 84
I don't know enough about these to know if it even has an EGR system. I looked the engine over and didn't see anything that resembles an EGR valve that I'm familiar with.

Anybody else have any ideas?
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Old 07-13-2020, 10:08 AM   #4
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Join Date: Sep 2014
Location: Eustis FLORIDA
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Year: 1999
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Chassis: Freighliner FS65
Engine: Cat 3126
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No egr on a 99.
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Old 07-13-2020, 10:15 AM   #5
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Year: 1984
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Engine: 6.9 International
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Sounds like a load of some sort is being applied to the engine. Like the alternator being turned on or some other load. You can remove the valve cover and do a valve lash inspection/adjustment.
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Old 07-13-2020, 11:28 AM   #6
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Join Date: Apr 2020
Location: New Mexico
Posts: 43
Year: 1999
Coachwork: Thomas
Engine: Cummins 8.3 ISC
I don't have any ideas, but I wanted to chime in with a "me too."
Mine is also a '99, and it does this noise change on every cold start. I haven't noticed whether it does it on warm starts, but I will look for it now.
It doesn't seem to have any effect on how well my engine runs.
I had also been guessing that it was some accessory kicking in, like maybe the air pump.
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