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Ken S
Dodge Dakota
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9/20/2010
19:45:15

Subject: Vacuum leak problem.
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V6 99' 4x4 149k mi

I have/think I have a vacuum leak somewhere. Whenever I go up hills the vents redirect the air and then starts blowing back out after I've topped the hill. The blower is still blowing. I have performance loss too.
Does anyone know if this is definitely a vacuum problem, and what lines I might can replace pretty easily to fix this. I've looked in the hayes manual, but can't find anything about vacuum lines.



JasonB
Dodge Dakota
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9/20/2010
20:39:09

RE: Vacuum leak problem.
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Yes. Vacuum leak.
The vents redirect to the default position (defrost).
If your cruise control cuts out at the same time, check the vacuum lines from the cruise module in the engine compartment back to where it connects with a "T" to the hose that goes to the vacuum reservoir from the brake booster.
Unfortunately, Dodge put the vacuum reservoir under the cowling, which means removal of windshield wipers and some other stuff to lift the cowl off.
I've done it. It takes some time and patience, but it's not too involved a procedure. Some of the plastic clips unscrew (the ones that look like a torx driver would fit) and some of them snap into place.
Also. Inside the cab. The knob that changes the flow of air to the different vents is a vacuum switch, and one of the half dozen or so hard plastic vacuum lines could be cracked.
The vacuum lines in the engine compartment and under the cowl are the ones I would check first, because they're the ones constantly subjected to engine heat and effects of weather.




JasonB
Dodge Dakota
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9/20/2010
20:53:51

RE: Vacuum leak problem.
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Also check the hose between the brake booster and the vacuum port on the engine side of the throttle body or intake manifold.
Another thing: the hose connector on the brake booster is a check valve, so if you have a vacuum leak between booster and vacuum reservoir, you won't hear air getting sucked in when you pull the hose (not the one from the engine) loose from the booster.
If you have a vacuum leak, you may be able to find it by running the engine for a bit, then shutting it off and listening for the leak. A helper with good ears is a definite benifit when using this method.

Good luck.





Bob Lincoln
Dodge Dakota
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9/21/2010
08:25:52

RE: Vacuum leak problem.
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Has it always done this, or is it recent? There was a check valve re-design on some Chrysler products, a larger valve solved this issue on many of the cars and trucks. There was a TSB on this issue.



Ken S
Dodge Dakota
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3/05/2018
08:56:53

RE: Vacuum leak problem.
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Wow, this thread is old. I'm gonna bring it
back from the dead.
So, I never have tried to fix the vacuum leak.
I am driving my truck more now, and it's really
bothering me how the vents keep messing up
while I'm driving, so I've decided to
investigate again. The problem is getting worse
too.
So I've taken it to a couple of places, and
they say there's no vacuum leak. I have
inspected the lines in the truck under the dash
the best I could without taking out the dash.
The mode switch seems to be working fine. I'm
getting vacuum pressure on the line that comes
through the firewall. I can unplug it at that
point and feel it.
I have replaced 2 check valves, one on the line
coming out of the booster, and the other on the
line that is split off to go to the air
controls. (I really figured it was this one)
BUT both old ones seemed to work fine, I
replaced them anyway.
The local autocrats store couldn't find the
correct valve that goes into the brake booster.
The next thing on my list is the vacuum
reservoir. I'm not sure how this would directly
connect to having the issue with the air
controls, but maybe it does. My cruise control
doesn't seem to have any issue. And it seems
that the reservoir is more for the cruise
control. But still the next cheapest thing to
check.



Ken S
Dodge Dakota
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3/05/2018
12:49:32

RE: Vacuum leak problem.
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Ordered a vacuum reservoir.
And no, I didn't check it first to see if it's
bad. Heck with it, I just ordered it.
Post what happens when I get it replaced.



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