my defroster has a mind of its own...

So I'm cruisin down the highway at 75 mph and the Jeep is doing pretty good having one of its good days on power. Quick run down of the Jeep 97 XJ 4 dr 4.0L auto 4x4 3.5" lift 31" BFG muds on black rock crawlers roof rack etc. exhuast K&N FIPK 99 intake manifold, few other goodies. Anyway when I would get up to hills and have to put a little more into the skinny pedal to keep speed would get to that point right before it would down shift keep it from wastin too much gas. When I would do this I would all of a sudden feel air blowin out the windshield defroster vent but the climate control was completely off no fan blowin. The air comin through had the force of about the 2 fan setting. When I would let off the gas some again after gettin over the hill the air would stop comin through. I know there is the issue with the vaccum leak and the air only comin out the defroster vent when u turn the blower on but I have no problem like this just the one I described earlier. So anyone think they might know what my problem is?

Even with the fan 'off' you get air forced through the vents from outside, yes, you have a vac leak or low vac. Start checking lines, it can only get worse. At least the XJ defaults to the def mode, the TJ defaults to the floor mode and in the winter it's usually the defrosters you really need. I would much rather be a bit cold than blind.

you need to fix the vacuum leak. as rpms or load goes up, vacuum goes down. the loss of vacuum could be opening up a blend door and allowing air to come through the cowl.

So I checked every vaccum line and connection I could find and they all appear to be fine no visible cracks or holes. The two valves on the the vavles cover have a little wiggle room but they have always had that much room to move around since I have owned the Jeep which has been over 6 years. I know there is an issue with the vaccum canister thing in the front bumper and I had to remove the bumper to do some work recently and I had to unbolt it and move it around but I made sure to be careful and I didn't notice any cracks or holes while working with it. I will be honest and say I don't know if I put it back right side up (if there is one) but since there were no markings on which way was "up" I just remounted it and put the bumper back on. I have put the newer style 99+ intake manifold on and had to plug one hole on it with a rubber cap that was I got from autozone in the section where they had all the vaccum line stuff. I also had to extend a the vaccum line that comes out the fire wall and goes right into the top of the back corner of the original manifold. I put an L fitting onto the end of some vaccum hard plastic line and plugged that into the closest available hole that is located on the side of the manifold right under the throttle body. The L fitting fits pretty snug so I don't think its leaking but I just shoved the other end of the vaccum line that I cut for the extention into the original L fitting on the original line coming out the fire wall. It doesn't fit super snug but it seems like it would seal enough but I was gonna put a little silicon on it anyway for good measure. I do have an oil leak with the valve cover but its just a strong apparent seeping right now but not a dripping oil leak. I have the new seal to replace it I just havent done it yet. Am I overlooking something here? Is there a good way to find a leak in the vaccum system other than a visual inspection?

you can use a vacuum gauge to test for leaks.

have you checked the vacuum lines that run under the battery?

89xj said:

you can use a vacuum gauge to test for leaks.

have you checked the vacuum lines that run under the battery?

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Yea, that one gets eaten by battery splooge, it goes to the blimp behind the bumper, another method of testing is to use a smoker, it pumps smoke into the system and you look for leaks.

I didn't know that there was one running under the battery so I will definitely check that one today. Is there a cheap old school way of checking for leaks where I don't have to go out and buy a gauge or smoker or something? I am in college and on a tight budget.

Ben824 said:

I didn't know that there was one running under the battery so I will definitely check that one today. Is there a cheap old school way of checking for leaks where I don't have to go out and buy a gauge or smoker or something? I am in college and on a tight budget.

Click to expand...

A baster and a pack of camels.... and replace the bulb handle with as big a balloon as you can.

carb cleaner spray your lines when idle is affected your in the ballpark i really dont get the smoke thing how something leaking vacuum will be detected by smoke duh it just dawned on me you are speaking of doing it with engine off, makes sense