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Topic: Air exhausting at firewall valve (Read 496 times) previous topic - next topic

Air exhausting at firewall valve

I'm not sure if the link will work to the video but I've attached a picture of the small valve (below the black cannister/accumulator). Whenever driving this small valve exhaust every 10 seconds or so, I don't recall this happening before. Anyone have this happen before?


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Len Barron
1988 GV36 U280 3208T(250hp)/MT643
1972 Jeep Commando LS2/4L65e
2000 Chevy Express Hightop Campervan
LBZ Duramax /6sp Allison

Re: Air exhausting at firewall valve

Reply #1 –
obsolete vacuum generator

1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Air exhausting at firewall valve

Reply #2 –
Like craneman posted it is a vacuum generator utilizing air pressure through a venturi to generator a vacuum.  Diesel engines don't have vacuum from the manifold like a gas engine does so they used a vacuum generator.
Forest & Cindy Olivier
1987 log cabin
2011 Roadtrek C210P
no longer 1999 36' U320 build #5522
2013 Rzr 570 & 2018 Ranger XP1000
2006 Lexus GX470
2011 Tahoe LT 4x4
Previous 1998 45' 2 slide Newell, 1993 39' Newell

Re: Air exhausting at firewall valve

Reply #3 –
is it normal for it to vent like that (every 10 secs or so)? or does that mean there's a vacuum leak downstream causing it to work more than normal?
Len Barron
1988 GV36 U280 3208T(250hp)/MT643
1972 Jeep Commando LS2/4L65e
2000 Chevy Express Hightop Campervan
LBZ Duramax /6sp Allison

Re: Air exhausting at firewall valve

Reply #4 –
Quote from: len.barron –
...does that mean there's a vacuum leak downstream causing it to work more than normal?
Since this is "new" behavior, I would say your guess is a good possibility.  Check all the vacuum lines you can see or reach for cracks or loose connections.  There are some vacuum lines under the lift-up dash cover - attached to the heater/air conditioner controls.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air exhausting at firewall valve

Reply #5 –
I was pretty sure it was new, so, after reading through a bunch of the related threads I saw that heater controls position (setting static in one spot) might be the cause, sure enough after I cycled it through the different positions it cleared right up, now it only cycles after a couple of vent position  changes (from "off" to "vent" to "heat") then it will cycle a single time to recharge the canister with vacuum.
Thanks to all for the help! That vacuum generator isn't in the air system drawing..
Len Barron
1988 GV36 U280 3208T(250hp)/MT643
1972 Jeep Commando LS2/4L65e
2000 Chevy Express Hightop Campervan
LBZ Duramax /6sp Allison

Re: Air exhausting at firewall valve

Reply #6 –
There are also a number of 12 VDC vacuum pumps-- for example on Ford trucks with diesel engines.  Just another option if the air/vacuum generator is $$$ to repair/replace.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air exhausting at firewall valve

Reply #7 –
Quote from: wolfe10 –
There are also a number of 12 VDC vacuum pumps-- for example on Ford trucks with diesel engines.  Just another option if the air/vacuum generator is $$$ to repair/replace.
My Duramax Express Van uses one for the heater controls...of course GM saw fit to install it directly below the battery so if you have any acid leak it eats it up..  ::)
Len Barron
1988 GV36 U280 3208T(250hp)/MT643
1972 Jeep Commando LS2/4L65e
2000 Chevy Express Hightop Campervan
LBZ Duramax /6sp Allison

Re: Air exhausting at firewall valve

Reply #8 –
Speaking of vacuum generator--is that what is under the entry step on my coach and what does it control?  Also, has anyone moved it some other place to better utilize space under step?
Thanks
Chris
1999 U 320 DGFE
Build Number 5523
Chris & Elka Lang
In the field, Lonoke AR

Re: Air exhausting at firewall valve

Reply #9 –
It controls the HVAC registers. I moved mine to the back side so I could have the step conversion.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Air exhausting at firewall valve

Reply #10 –
Our 91 GV has a vacuum pump up front next to the AC cooler.  Have a great day  ----  Fritz
Fritz & Kathy Johnson
1991 36'