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KnuckleBuster76
Active Member

45 Posts

Posted - 05/10/2017 :  08:03:02 AM  Show Profile  Reply with Quote
Running into a head-scratcher with the air system. Another branch brought me a bus with an air-building issue. Air builds GREAT, until it purges at 145psi (WAY too high, I know, I'll get to that). Once it purges, the air pressure will not build unless you rev it up to 2400rpm. Once it starts to build, you can drop it to idle and it builds air like a champ. Can run it like a dream unless it purges. Once it purges, it won't build again unless you rev to 2400. I figured the governor or air dryer (purge valve). The other shop put a governor on it already. I swapped out the dryer with no luck. I highly doubt it's a compressor issue. In my experience, they're good or bad, never intermittent.

Thomasbus24
Administrator

USA
4544 Posts

Posted - 05/10/2017 :  08:47:10 AM  Show Profile  Reply with Quote
Unless it's a 6.7 Cummins with a...ummm...Wabco maybe? compressor with a reed valve in the head.

We've had 2 now (Blue Birds) that got gummed up and became intermittent problems. Dealer has seen it dozens if not more times. We bought a head and gasket set the first time, installed, cured. Soaked old head in solvent for a week and put on shelf. Next bus, used that head and a gasket set, soaked gummed up head, put on shelf. It's going to be a cycle I'm afraid.

Your results may vary.
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KnuckleBuster76
Active Member

45 Posts

Posted - 05/11/2017 :  09:41:29 AM  Show Profile  Reply with Quote
It IS the Cummins with a Wabco. Wasn't looking for a cyclic issue. Neverending, isn't it?

"Just... I dunno... Just fix it."
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Thomasbus24
Administrator

USA
4544 Posts

Posted - 05/11/2017 :  09:56:22 AM  Show Profile  Reply with Quote
A neighbor had some luck (for now) by pouring some type of solvent cleaner into the ports of the compressor. Don't know that I'd suggest this, but it worked for him.
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woodster
New Member

7 Posts

Posted - 05/12/2017 :  12:53:24 PM  Show Profile  Visit woodster's Homepage  Reply with Quote
we have had this problem,We fill the compressor with transmission fluid let it sit over night then run it and change drier.It works pretty good
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KnuckleBuster76
Active Member

45 Posts

Posted - 05/16/2017 :  05:10:17 AM  Show Profile  Reply with Quote
Was just informed by a guy that a sticking unloader valve is very likely the problem. He's sending the Cummins bulletin to me now. Supposedly I unhook the air dryer and dribble ATF into the compressor intake as it's running. Will let y'all know if it works!

"Just... I dunno... Just fix it."
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earl1412
Senior Member

101 Posts

Posted - 05/17/2017 :  2:48:29 PM  Show Profile  Reply with Quote
quote:
Originally posted by KnuckleBuster76

Was just informed by a guy that a sticking unloader valve is very likely the problem. He's sending the Cummins bulletin to me now. Supposedly I unhook the air dryer and dribble ATF into the compressor intake as it's running. Will let y'all know if it works!


How many miles are on these buses? I have ten of this type of setup, and would like to know when to expect this to start happening.
Also, could you post the Cummins bulletin number, so I can get a copy from my dealer? Thank you
earl
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Thomasbus24
Administrator

USA
4544 Posts

Posted - 05/18/2017 :  04:25:44 AM  Show Profile  Reply with Quote
Yeah, please get us the number for this. Taking the head off in a transit isn't our idea of a good time.

Mine have been in the neighborhood of 100,000 miles when it happens.
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tigger2
Advanced Member

USA
469 Posts

Posted - 05/31/2017 :  1:45:42 PM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
We fixed this issue on our units by moving the intake for the compressor to a point further from the EGR inlet to the intake manifold. On our HDX's we welded a bushing to the CAC pipe just past the charge air cooler and routed the hose to it there. on the conventional units we used the new pipe and new hose arrangement from the later units.





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LRed
Active Member

10 Posts

Posted - 06/06/2017 :  12:40:43 PM  Show Profile  Visit LRed's Homepage  Reply with Quote
Does anyone know the part number(s) for the CAC pipe on the newer buses?
Thank you in advance.
LRed
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earl1412
Senior Member

101 Posts

Posted - 06/08/2017 :  1:27:06 PM  Show Profile  Reply with Quote
quote:
Originally posted by LRed

Does anyone know the part number(s) for the CAC pipe on the newer buses?
Thank you in advance.
LRed


The BB P/N for my 2016 Vision with 6.7L ISB is 10033156 Described as 3.00 OD With 1.00 OD port.This is just the TEE, not the rest of the pipes and hoses
Best I can come up with.

Edited by - earl1412 on 06/08/2017 1:30:38 PM
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LRed
Active Member

10 Posts

Posted - 06/09/2017 :  04:24:56 AM  Show Profile  Visit LRed's Homepage  Reply with Quote
Thank you!
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KnuckleBuster76
Active Member

45 Posts

Posted - 06/16/2017 :  05:31:05 AM  Show Profile  Reply with Quote
Yeah... so an update. Using the ATF trick worked... for a bit. Got a call and it's happening again. Time to swap the compressor, I think.

"Just... I dunno... Just fix it."
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Thomasbus24
Administrator

USA
4544 Posts

Posted - 06/19/2017 :  05:32:58 AM  Show Profile  Reply with Quote
How much a nightmare is the entire compressor V just the head?
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