Author Topic: 350 cummins start up sounds  (Read 4366 times)

Robert Paisley

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350 cummins start up sounds
« on: June 30, 2015, 03:48:25 PM »
Two little things of interest:
1. I learned yesterday that I can tap the Accel button on my cruise control and control the idle speed.
A couple of bumps of the button and the idle speed can be brought up to 1000rpm. The air tanks fill within a few seconds.
Turn off the cruise control and the idle goes back down. Handy little function.

2. When I start the 350 Cummins (CAPS ISC), it sounds very smooth and quiet for the first few seconds of running.
Then something changes and it reverts to its normal throaty rattling diesel idle sound. Is there some kind of special fuel mode or something during the first few seconds of running that causes the sound change?

Thanks,
Robert
« Last Edit: June 30, 2015, 03:58:45 PM by Robert Paisley »

Fred Brooks

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Re: 350 cummins start up sounds
« Reply #1 on: June 30, 2015, 05:10:13 PM »
       Hi Robert,

   1- Not sure if your coach has a "smart wheel" but here is the way it was originally engineered: start the coach, turn the cruise control switch on, Hit the resume button once and the rpm should jump from 650 to approx 1000. Not only is it a good "fast Idle" to build air pressure but a great way to cool off your turbocharger after pulling into  a rest area off the interstate especially if you were just pulling a grade with a toad and the turbo is hot. Keep in mind that the turbo is "oil pressure dependent" . Just imagine you just pulled a 6 percent grade and pulled into a rest area and the turbo is 1100 degrees and spinning 10,000 rpm and you turned off the engine and cut off the oil pressure to the turbo ball bearings. Ouch is what that turbo is thinking!
   2- I think the sound change is the pressure change you hear in the aftercooler charge system. I would ask Dave Atherton for his wisdom because this more in his "wheel house"

              Regards Fred


Fred & Cindy Brooks
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Roy C Tyler

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Re: 350 cummins start up sounds
« Reply #2 on: June 30, 2015, 07:21:43 PM »
Robert
My 350 Cummins does the same thing when I first start it.  I thought maybe is was the Aladdin speaker coming on which is back by the engine compartment.  Actually never gave it much thought.

Dave Atherton

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Re: 350 cummins start up sounds
« Reply #3 on: June 30, 2015, 10:25:19 PM »
Robert, with your Cummins ISC engine your fuel injection system is called a CAPS System.
Looking in from the back of your motorhome and to the right side of engine about mid way
up on the engine you will see a square housing with looks like ( 2 ) spark plugs sticking out
of the square housing. These two thing is what sends fuel under high pressure to your injectors.
The first one in front will fuel cylinders 1, 2, 3 than the second spark plug looking thing, will
fuel cylinders 4, 5, and 6. In the base of these injector actuators the square block this is where
There is many poppets  and check valves. ( the square housing is a pressure accumulator).
There is a certain noise level you will hear just the way system is made and pretty much normal.
Note: do not remove the injector actuators from that square housing in any way. The injectors
actuators and housing come as one unit and is very pricy. That is where your noise is coming from.
Dave Atherton Retired Cat Mechanic