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12 Valve 2nd Gen Dodge Cummins 94-98 Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with P7100 Injection Pumps

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My 4x4 doesn't engage and all my heat/AC comes out of the defrost vents. I assume I have a vacuum leak somewhere. Is this a correct assumption and if so where should I start looking and does anybody have some good tips or tricks?... JOIN NOW TO REMOVE TRACER

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  #1  
Old 09-27-2012, 06:07 PM
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Smile vacuum leak or???

My 4x4 doesn't engage and all my heat/AC comes out of the defrost vents. I assume I have a vacuum leak somewhere. Is this a correct assumption and if so where should I start looking and does anybody have some good tips or tricks?

DieselObsession76's Sig:Project truck: 1st gen Cummins, 518 auto, PSD I/C, HX40, Boost/Pyro, intake and exhaust, Go fast screw maxed, smoke screw down and a fuel pin for now. Soon to be HX40/HT3B with enough fuel to break stuff
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  #2  
Old 09-27-2012, 09:10 PM
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I know the heat and ac coming out the defrost is a common dodge problem my truuck and all my buddys trucks do it im not sure why mine does blow thru the other ones sometimes but my 4x4 works great and so do my buddys trucks I wouldn't think that's connected. I think it would be a different problem with the 4x4 . Maybe the actuator on the front axle that's a common problem with them . Personally i thi.nk the heat and ac prob is one of dodges common electrical problems with the unnit on the dash BC mine works sometimes out of the other vents if i beat on it buive never tried to replace it. Hope that helps a little bit ..
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Old 09-27-2012, 09:13 PM
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There is a vacuum line that runs across the top of the fire wall to the passenger side and then enters the cab. Most of the time it is by the turbo where is pinches shut due to the high temp in that area. If not, check the lines going to and from the t-case. Use a vacuum gauge tool or inspect them yourself. In general it would be good to check all the vacuum lines and connections.

97DodgeJW's Sig:1997 Cummins QCLB 4x4, Stock 12v, KDP killed, 4" from turbo back, delete silencer ring, K&N intake elbow, Donaldson air filter, NV4500, 2.5" leveling kit, Bilstien 5100 shocks, longer trailing arms
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Old 09-27-2012, 09:27 PM
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Would start with the vacuum line at the top of the fire wall. I had the same issue

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  #5  
Old 09-27-2012, 10:06 PM
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So what you guys are saying that these 2 probs are one problem? I know of 4 trucks that have the same heat and ac issue but the 4x4 doesn't skip a beat could there be a dfrent prob with our trucks?
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Old 09-27-2012, 10:27 PM
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Its kinda one in the same, they both operate on vacuum. The "defrost only" problem is caused by a bad vacuum to the actuator that operates a flap door to direct the airflow, or the actuator itself is bad -which is the problem I currently have. I still have cruise and 4x4, just no vents.
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Old 09-28-2012, 01:57 AM
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Thanks for the replies fellas. I'll get on that as soon as the suns up and I'll let you know what I find
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Old 09-28-2012, 08:00 AM
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Ok 3 questions. 1: what hose am I looking for, 2: what the hell is the blocked off one, and 3 those hoses weren't put on by dodge were they?
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  #9  
Old 09-28-2012, 09:14 AM
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first pic with the plug looking thing on top is your axel breather.. second pic is of the coolant lines going in cab for heater core.. look for a thin hard black plastic line goes from end to end of the truck has a couple branch offs that lead down to the trans area and one inside

gyayo2012's Sig:96 auto, bhaf, 4" t-back, #6 plate, 3k gsk! Boost elbo, Boost,Egt,Transtemp guages, Bilstein5100's, 98 hd t style steering,rear dana 70 disk conversion!

95 dump 4x4 auto 410s pretty much stock... has a 160 pump put a 180 plate in and slid it ff. bhaf 3" strait piped
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Old 09-28-2012, 11:47 AM
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Originally Posted by gyayo2012 View Post
first pic with the plug looking thing on top is your axel breather.. second pic is of the coolant lines going in cab for heater core.. look for a thin hard black plastic line goes from end to end of the truck has a couple branch offs that lead down to the trans area and one inside

I'm sorry I'm probably being impossible but do you have a better description of this line? And a place I can find it and follow it? I know absolutely nothing about this whole vacuum system

---AutoMerged DoublePost---

Scratch that I found em all after some more research... they're pretty easy to find actually... but now I need to know how to test them all.

Last edited by DieselObsession76; 09-28-2012 at 11:47 AM.. Reason: Automerged Doublepost
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