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04-19-2023, 02:18 PM
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#1
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Junior Member
Join Date: Apr 2023
Posts: 5
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Pacbrake problems
I have a '96 Mountainaire with an 8.3 Cummins. The exhaust brake works when it's supposed to, actually too good for my liking. However, on really long downhills and with no throttle input the engine will stall. I pulled the air cylinder off and it appears to be ok. The exhaust brake mechanism works freely as well.
There is a small "Humphrey" brand air valve on the air intake end of the cylinder. It may be some type of dump valve and I thought that may be the problem. Has anyone encountered this problem? I'm hoping it's not electrical.
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04-19-2023, 06:10 PM
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#2
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Senior Member
Join Date: Jul 2018
Location: Southeast Texas
Posts: 1,721
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Pacbrake problems
Does it also stall if going downhill without the exhaust brake on?
When my coach is on exhaust brake or foot off pedal, there is zero fuel flow to the injectors so motor is “dead” until i press on throttle again. Not sure if they’re all that way. Im wondering if it is more of an injection pump /fuel issue than exhaust brake issue.
__________________
1998 HR Endeavor Cummins ISB 275 / Banks Allison 3060
20014Jeep Wrangler JKUR with M&G air brake with breakaway
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04-19-2023, 09:13 PM
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#3
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Senior Member
Join Date: Jan 2020
Posts: 236
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Quote:
Originally Posted by Jon_C
Does it also stall if going downhill without the exhaust brake on?
When my coach is on exhaust brake or foot off pedal, there is zero fuel flow to the injectors so motor is “dead” until i press on throttle again. Not sure if they’re all that way. Im wondering if it is more of an injection pump /fuel issue than exhaust brake issue.
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The Humphrey valve is simply a quick release valve that helps the exhaust brake to close rapidly. Mine developed a leak in the rubber and the exhaust brake was noisy and inefficient.
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04-19-2023, 09:41 PM
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#4
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Junior Member
Join Date: Apr 2023
Posts: 5
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Coach runs great. Doesn't stall any other time. If I use the exhaust brake for short bursts its ok. Only on really long hills that it stalls. I was also wondering if the idle is too low. It idles at just over 500 rpm.
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04-19-2023, 10:04 PM
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#5
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Senior Member
Join Date: Oct 2017
Location: Courtenay BC
Posts: 151
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Turn the idle up to 650 and see if that helps 500 is pretty low
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04-19-2023, 10:59 PM
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#6
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Senior Member
Join Date: Jul 2018
Location: Southeast Texas
Posts: 1,721
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Pacbrake problems
500 is low as mentioned set to 650.
When you reach bottom of hill and step on pedal it should give enough fuel for it to run and accelerate, does it do this or not?
If not maybe exhaust brake is sticking on long grades when closed for longer period for some reason. When was the last time you lubed the brake? It’s recommended to lube with pacbrake lube every time you change engine oil.
And what does it take to recover from the stall?
__________________
1998 HR Endeavor Cummins ISB 275 / Banks Allison 3060
20014Jeep Wrangler JKUR with M&G air brake with breakaway
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04-20-2023, 12:45 PM
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#7
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Junior Member
Join Date: Apr 2023
Posts: 5
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The engine fires right away. I think you may be right. The idle is too low and when the exhaust brake is on it goes lower and runs out of fuel. Now I have to find the idle screw. Not much room in there! I definitely need to lube the system as it hasn't been done by me. 160K on unit. I've put about 30K.
The exhaust flap doesn't appear to be binding at all. Moves freely.
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04-20-2023, 01:42 PM
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#8
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Junior Member
Join Date: Apr 2023
Posts: 5
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Does anyone know where the idle adjustment is located?
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04-20-2023, 06:58 PM
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#9
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Senior Member
Join Date: Aug 2001
Location: North America somewhere
Posts: 30,903
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Quote:
Originally Posted by KamKid
Does anyone know where the idle adjustment is located?
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Found online: "Do you have the Bosch inline injection pump or the CAPS fuel system? The caps is non adjustable and set through the ECM programming and the Bosch pump has a low idle stop screw on the throttle control lever but is preset by the injection shop when the pump is set up on the test and calibration bench. Any adjustments now will be compensation for wear in the injection pump."
__________________
2000 Winnebago Ultimate Freedom USQ40JD , ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA. " My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
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04-22-2023, 02:49 PM
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#10
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Junior Member
Join Date: Apr 2023
Posts: 5
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Found the adjustment....finally! Set idle at 650 and have yet to try it. Will update after trial. Thanks to all for the feedback, it was helpful.
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Linear Mode
