I have been noticing a valve train noise coming from my engine, It seemed to start when i put on the CAI and exhaust, or at least thats when i noticed it. Im not to concerned about that because I do plan on doing a cam swap next spring with all new lifters and valve springs.

The issue thats bugging me is when im running my AC I have noticed that when I hit a hill or put the engine under load, my AC moves from the dash vents to the defroster. My first thought was check valve so today i pulled out the check valve by the heater lines. I could only blow through it one way. Must be good right. Is there another check valve that would be in this system somewhere or am i way off base here? I really hate chasing vacuum leaks. Can a bad plenum cause this? Im almost to the point of pulling out the carb clean and spraying the vacuum lines.

 

You've probably got a minor leak somewhere downstream of the check valve -- there's just nowhere near enough reservoir there to hold everything in place for long with even a tiny leak, and there are five (if memory serves) vacuum lines leaving the control in the dash to the various motors so there's lots of surface area on those old, dry lines to create hassles.

If it's really annoying you, there's another check valve that can be obtained from the Dodge dealership that'll add another cubic inch or so of reservoir capacity, but you'll have to mickey-mouse it into place because the nipples are smaller than the hoses on our trucks. The doors will still flap, but not as quickly. Alternatively, you could ****** a smallish vacuum reservoir from a junkyard vehicle and tee it into your system, downstream of the check valve. I'd go so far as to add another cheap generic check valve right up next to that reservoir so it can't cause you any running problems when the factory valve pukes. I've done this in the past on other of my trucks, mainly to keep the heat coming into the cab when it's bitter cold in the wintertime.

 

when u say downstream u mean toward the HVAC right, I just wanna make sure im going the right direction, I did find a second check valve just off the intake manifold on the pass. side. Its actually in one of lines feeding the second check valve up by the heater hoses. I havent had a chance to get under the hood far enough today to check that one. I also saw a funny looking thing on a vacuum line just behind the manifold by the distributer. Kinda looked like a broken check valve or something. I want to look under the hood of another 5.2 to see if it has the same thing. Ill try to get a pic tomorrow of it.

 

Yep -- by "downstream" I actually do mean closer to the vent control than to the intake manifold. I suppose that technically it's upstream...

Is this the widget that looks like it might be broken?



It shouldn't look broken.

 

that one is the one i checked, the one that looks broken is on the other side of the intake manifold beside the distributer, I had a tooth pulled yesterday and the meds are keeping me from looking farther into this, I dont want to mess anything up, I tend to be a little tipsy and absent minded. Im putting it on hold for a few more days. Ill be back under the hood this weekend.

 

Might want to visit the local junkyard, and check around for vacuum reservoirs. Plumb one in downstream from the check valve, with a T fitting. Might just be masking symptoms, but, would fix if for the foreseeable future.