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I have the wild vent syndrome.. help on vacuum leak!!
11-02-2010, 07:31 PM
Post: #1
Exclamation I have the wild vent syndrome.. help on vacuum leak!!
I've seen a few threads in here about the vents that switch back and forth from the setting its on to the defrost mode upon acceleration. I am having that problem too, but havent found the answer to it. I too think its a vacuum leak however im not sure if i have a bad heater core as well. My heater blows very mildly warm air for about 10 sec at a time and then go cold. I'm assuming there is a vacuum that opens and closes the doors to the heater core and all the vents. I was also told to install a check valve in the line that runs into the fire wall to the HVAC unit.. however previous threads stated that solution only worked for a day or 2 and then the problem persisted. HELP or any tips will be appreciated .. THANKS A BUNCH






1996 Dodge Ram 1500 reg cab 4in clayton lift 3/4 ton durability and 33 Grabber AT2s.
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11-02-2010, 07:39 PM
Post: #2
RE: I have the wild vent syndrome.. help on vacuum leak!!
I would agree on the vacuum leak for the vents. The default setting is the defrost position, does it switch rhythmically or when you put a load on the engine or when you do a specific thing?

Use a can of carb cleaner, run it at idle, and spray around the vacuum lines, when you find the leak, the RPMs will increase due to the spray. Most leaks are on the 4x4 actuator since the lines are brittle and subjected to more of the elements and movement than those in the engine compartment.




Ooh Rah Devils!
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1998 Dodge Ram 2500 Quad 4x4 V10-White DT Trac bar, Borg box & shaft, DOR steering brace, headers, FIPK, Road Armor Front/Rear bumpers...so far
1998 Dodge Ram 2500 Quad 4x4 Sport V8-Black
2.5" Skyjacker, 2" BL, Alum Radiator, EMS hub conversion, dual ARBs, 35 spline alloys FR/R, 4.88s, Magnaflow, Borgeson shaft, 37" BFG Bajas on 24 bolt H1s, custom bumpers , bedlined rockers & bed
1999 Jeep TJ, Project "Recycled Ram"
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11-03-2010, 07:38 AM
Post: #3
RE: I have the wild vent syndrome.. help on vacuum leak!!
So the vacuum leak could be anywhere? It changes from vents to defrost when I bring up rpms or go up
hills. When the throttle is let off it switches back to
vents. say if the leak is close to the hvac unit how would that make the idle go up with the vacuum direction headed toward the cab?
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11-03-2010, 08:29 AM
Post: #4
RE: I have the wild vent syndrome.. help on vacuum leak!!
vacuum sucks air towards the vacuum source (the motor), so if you put a flammable spray near the leak it will go to the motor and burn. You could have a bad plenum leak (pull your air hat and check you TB for oil), your 4x4 lines could be bad(see if your 4x4 works for starters), your brake booster could be bad, your brake check valve could be bad. There's too many vacuum sources to pick one. The are all interconnected, so you just need 1 leak...Dunno




Ooh Rah Devils!
Dueling Dodges Rams
1998 Dodge Ram 2500 Quad 4x4 V10-White DT Trac bar, Borg box & shaft, DOR steering brace, headers, FIPK, Road Armor Front/Rear bumpers...so far
1998 Dodge Ram 2500 Quad 4x4 Sport V8-Black
2.5" Skyjacker, 2" BL, Alum Radiator, EMS hub conversion, dual ARBs, 35 spline alloys FR/R, 4.88s, Magnaflow, Borgeson shaft, 37" BFG Bajas on 24 bolt H1s, custom bumpers , bedlined rockers & bed
1999 Jeep TJ, Project "Recycled Ram"
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11-03-2010, 11:14 AM (This post was last modified: 11-03-2010 06:22 PM by mopardriver12345.)
Post: #5
RE: I have the wild vent syndrome.. help on vacuum leak!!
Yeah I've realized its a tuffy. Now I know a good amount on steering and suspension but still learning engines. I'm assuming the plenum is under the tb.. if I have blow by in the valves that could also create too much vacuum?or am I wrong. My brakes are fine would I notice something funny with the brake booster or cv going bad? the 4wd works great i use it often. Again thanks for all the help
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11-03-2010, 06:21 PM
Post: #6
RE: I have the wild vent syndrome.. help on vacuum leak!!
New news that might be able to help everyone with suggestions. When I'm on the road and at cruising rpms or higher, and the heat is on any vent setting and fan is on,.. i hear a slight, very high pitched whistle seems to be coming from under the dash but cant really tell for sure. When the heat selector is in the off position it does not whistle, and when its on any selection, and the blower is off, it doesnt make the noise either. .. if that makes sence. ... Could that be a vacuum line whistling from under the dash? or is that the sound of the blower motor pushing air through? it doesnt make the noise at an idle, thats why i figured its a vacuum line. any help is welcome. Thanks!!
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11-16-2010, 08:38 AM
Post: #7
RE: I have the wild vent syndrome.. help on vacuum leak!!
(11-02-2010 07:31 PM)mopardriver12345 Wrote:  I've seen a few threads in here about the vents that switch back and forth from the setting its on to the defrost mode upon acceleration. I am having that problem too, but havent found the answer to it. I too think its a vacuum leak however im not sure if i have a bad heater core as well. My heater blows very mildly warm air for about 10 sec at a time and then go cold. I'm assuming there is a vacuum that opens and closes the doors to the heater core and all the vents. I was also told to install a check valve in the line that runs into the fire wall to the HVAC unit.. however previous threads stated that solution only worked for a day or 2 and then the problem persisted. HELP or any tips will be appreciated .. THANKS A BUNCH






1996 Dodge Ram 1500 reg cab 4in clayton lift 3/4 ton durability and 33 Grabber AT2s.
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11-16-2010, 08:42 AM
Post: #8
RE: I have the wild vent syndrome.. help on vacuum leak!!
i had the same problem.put in new check valve helped for one day i found there is a second check valve a little closer to the engine changed that one and its been fixed all summer good luck
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