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Old 12-11-2020, 08:17 PM   #1
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ISC350 Startup Sounds

Something I have asked my Freightliner guys about, only to be told, “That’s normal, don’t worry”. When my coach starts up, there is a “quiet” period, of from 7 or 8 to 20 or so seconds, then there is a new noise that starts up, which I think of as a “clattering” sound.
I tried to capture a recording of it. The sound changes right at 12 seconds into this short .wav file. It’s the added noise that begins at that point that has me puzzled. Is this actually “Normal”? Is it an air pump sound? Is something knocking somewhere? Is my rig about to self destruct?

I would love to hear what more knowledgeable folks figure is going on here.
Attached Files
File Type: wav Cummins_ISC350_Startup.wav (895.9 KB, 11 views)
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Old 12-11-2020, 09:45 PM   #2
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Well, BUMMER! Thought I succeeded in uploading that, but now I cannot get it to ‘play’. Will try again tomorrow from another computer.
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Old 12-11-2020, 09:49 PM   #3
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I could play it, Sounds normal to me
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Old 12-11-2020, 11:24 PM   #4
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That is the air compressor starting and running. Mine sounds like that too, like it's gonna throw a rod. Observe, when air pressure reaches set point the air dryer will purge and the compressor goes into bypass mode the sound quiets.
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Old 12-12-2020, 10:26 AM   #5
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If it’s a Caps pump engine it normal. It changes the timing a few second after startup.
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Old 12-12-2020, 10:43 AM   #6
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Its your air compressor, it received a signal from the computer, low air turn on pump.
Watch your air gauge, if its under the set amount, it turns on, it should pump up to ~ 120.
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Old 12-12-2020, 10:44 AM   #7
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Quote:
Originally Posted by Ray,IN View Post
That is the air compressor starting and running. Mine sounds like that too, like it's gonna throw a rod. Observe, when air pressure reaches set point the air dryer will purge and the compressor goes into bypass mode the sound quiets.
Yes^^, the compressor kicking in. Normal.

However, after listening again, it could very well be the valve timing. I went with compressor because of your mention of "clanking" though I did not hear that element of the sound. If the sound disappears after the compressor purges, you will know.

Regardless, either cause is normal and that's really all you need to know.
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Old 12-12-2020, 10:50 AM   #8
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If it’s a Caps pump engine it normal. It changes the timing a few second after startup.
There was a thread on the subject a while back. As I recall, the consensus was timing and not the air compressor. My engine makes the same sound even when the air tanks are full.

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Old 12-12-2020, 11:12 AM   #9
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There was a thread on the subject a while back. As I recall, the consensus was timing and not the air compressor. My engine makes the same sound even when the air tanks are full.

Bill


Retarded timing for easier starting, then advance to control emissions once ECM sees oil pressure for set pre-detirmined time.

Just drive it.
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Old 12-12-2020, 12:31 PM   #10
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Its your air compressor, it received a signal from the computer, low air turn on pump.
Watch your air gauge, if its under the set amount, it turns on, it should pump up to ~ 120.
Air compressors receive a air signal from a tank, to a air controlled governor. No electronics or computers involved.
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Old 12-13-2020, 12:17 AM   #11
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Thanks all around, you’ve both reassured me — this is not a sign of imminent engine failure — and given me some valuable tips for better understanding it.
It’s great to get so many quick replies.

Mike
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Old 12-15-2020, 10:54 AM   #12
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Completely normal sound. Agreed, it is noticeable and alarming when you first hear it. As others have said, it's the timing advancing after start up, about 10 seconds after a cold start.
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Old 12-15-2020, 12:19 PM   #13
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Completely normal sound. Agreed, it is noticeable and alarming when you first hear it. As others have said, it's the timing advancing after start up, about 10 seconds after a cold start.
Interesting, I always thought that noise was the compressor. Never thought much more about it.
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Old 12-15-2020, 12:40 PM   #14
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Air compressors receive a air signal from a tank, to a air controlled governor. No electronics or computers involved.
^This^

Also, if your air tank's were below about 90psi when you start the engine, the compressor will be loaded immediately. Not 7-20sec later.
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