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weird sound happening after stopping engine

December 04, 2017, 10:41:53 am

This sound (sort of like an electrical motor with dry bushings??) has happend the last 2 days after our long day of driving. All systems are working fine and no issues show up on VMs, but once key is off this weird noise happens for about 2 seconds or so and occurs again about a minute or 2 later. It seems to be originating from the air dryer/ D2/ compressor/ fuel pump area and I have tried to listen using a metal bar while touching these items but it refuses to happen untill I move this  "stethescope"?? Once engine has cooled somewhat the noise goes away. It is quite loud. As mentioned before after hearing it 2 days ago it has not affected the engine or system while running.
Any ideas out there would be appreciated. I said to Ruth that maybe time to trade to a Prevost as it was telling us something.
JohnH

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Re: weird sound happening after stopping engine

Reply #1 – December 04, 2017, 10:50:38 am

Have you turned the key back on after the engine stops to eliminate an electrical issue? In other words does it still make the noise with the key back on. Not actually hearing the noise I can only guess that something is releasing pressure, either fuel or air.

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Reply #2 – December 04, 2017, 10:54:26 am

John this may sound goofy but have you tried to bleed some air off but opening the valve just for a couple of seconds?

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Reply #3 – December 04, 2017, 10:56:28 am

John my air dryer will make a noise after shutting  the motor off . It's unloading air pressure doesn't last long. Sounds kind of like a long purge. Original Haldex dryer , completely rebuilt last year.

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Reply #4 – December 04, 2017, 02:37:50 pm

I thought it may be the dryer (and I rebuild it every 2 yrs-totally) and put my hand under Purge valve but did not feel anything there. Other comments I will store in brain till we leave here in March and try.
This noise comes on as soon as engine shuts down and lasts about 20 seconds, goes away for a minute or 2 then back on, then repeats this scenario a few times then stops altogether. Must be a pressure related thing but air gauges do not go down at all !!!
Thanks for feedback
JohnH

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Reply #5 – December 04, 2017, 02:42:54 pm

If tank check valves are working, a leak at the dryer will only remove air "up to" the tank.

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Reply #6 – December 04, 2017, 02:47:04 pm

John,
Ours makes a sound that is definitely air related. It happens between 5 and 15 minutes after shutting the engine down. It doesn't affect the readings of the dash tank gauges, but I do see movement in the wet tank gauge, which is tapped off of a D2 port. It has confounded me for awhile... I speculate that it may have something to do with my rebuilt air dryer, or less desreably, the compressor unloader.
Don

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Reply #7 – December 04, 2017, 02:50:46 pm

Don,

Could also be (at least partly) related to heat soak raising air system temperature an therefore PSI in the engine room air system components.

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Reply #8 – December 04, 2017, 03:02:59 pm

Hmm... interesting thought. I still have some air tightness issues to track down, it will be interesting to see if the sound persists after I rebuild the six-packs etc.
Don

"Don,
Could also be (at least partly) related to heat soak raising air system temperature an therefore PSI in the engine room air system components."

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Reply #9 – December 04, 2017, 03:23:03 pm

John,

On your wet tank you have an air line (1/4") that comes off the tank with a brass 90 and goes to your air dryer. Seems like it is labeled #50 (I am away from my prints now so this is from memory) The brass 90 has a spring loaded check valve in it. I have seen this check valve squeal and make noise like you describe.  I have removed this 90 and cleaned it and this stopped the noise. You will be able to hear it better on the passengers side of the coach right at the rear tires as the fitting you are looking for is closer to this side. The OEM prints that I have don't show this check valve but I have found it on several coaches.

Pamela & Mike

After thinking about it this one of the air lines that goes to the isolation valve on your air dryer.

A third thought after some more time to think:  You may need to remove the isolation valve and check the O rings on the piston to make sure that they are good, clean, slightly greased, and the piston is moving free in the bore.

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Reply #10 – December 04, 2017, 06:36:33 pm

Just for thinking purposes ---- Are you sure it is not the turbo coasting down  ---- bearing problem??  Have a great day  ----  Fritz

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Reply #11 – December 04, 2017, 06:42:19 pm

Turbo would spool down before you could shut it down and RUN to the back of the coach.

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Reply #12 – December 04, 2017, 08:08:16 pm

Pam and Mike, no Isolation valve on our Dryer,but, I think you and the others that are thinking it is something to do with the Dryer may be right. The sound is definitly coming from that location. As I mentioned before I will wait till we get home so I can get under it easy and yank the Dryer lines off to check it out.
Thanks all
JohnH

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Reply #13 – December 05, 2017, 09:20:14 am

Update, last night at 10pm ( over 24 hrs after shutting off engine) and fast asleep till that noise happened again for 2 short instances then stopped. I could also hear a slight "chattering" so think it is a check valve that was fluttering.
Checked the wet tank drain and only had dry clean air come out this am. Both tanks reading 95lbs at this time, so maybe the check valves and line from dryer to wet tank!! Ah well worry about something more important if I can find one.
John H

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Reply #14 – December 06, 2017, 10:14:18 am

Update on Update. Last night at midnight in this ever so quiet location we again got woken up by this stupid irritating noise and this time it would not stop. I got out and released all the wet tank air and it still continued so I feathered the brake pedal and drained that down. Finally it stopped! I was still showing 90 lbs in tanks after sitting for 2 1/2 days. Neighbours may be getting a bit mad at us??
Hope this is the end of it till we start up again at end of Feb for trip home.
JohnH

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Reply #15 – December 06, 2017, 11:00:11 am

If the sound is coming from vicinity of dryer, and you drain wet tank down to zero and the sound continues, then that means both your inlet check valves at front and rear tanks are inoperative, as well as the inlet check valve on the wet tank.

If all your air tanks are empty, and the weird noise returns tonight...I'd be calling Ghostbusters!

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Reply #16 – December 06, 2017, 12:35:10 pm

Yes after emptying tanks I lay in bed thinking it all through and my ideas changed as to what could be problem(from original) I will look into the schematics some time and try and see what may be causing it, but again will leave it alone till I can get under it on pit. I did change all check valves a couple of years ago but still may be that- who knows?
Thanks.
JohnH

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