Hello,

I'm on a big project ATM.
I just got done replacing valve cover gasket, ccv hoses and grometts, clean throttle body, radiator replacement, water pump, thermostat, timing chain and guide, front main seal.

In this process I found a hose coming out from where the battery cover is at the bottom. In the picture you can see it. It' s not the radiator overflow I moved that out of the way so this could be seen. I also pulled the head light and the tee is there with all hoses connected and conencting to an actuator.
One line is going to the vaccuum box under the headlight its connected. And the vacuum line going from the actuator is going to the cruise control line.

This hose has me entirely puzzled where it goes!
And pics would be helpful or references. I did include a screenshot.

Any idea?

THis is a 1999 Jeep grand cherokee Laredo.

 

That hose goes to a vacuum reservoir that's built into the battery tray. Or maybe not after reading your post again.

 

It might be a drain from the battery box to get rid of battery acid if the battery leaks or cooks over. IDK about jeeps but even my lawn tractor has one.

Busted, the WJ's vacuum reservoir is a squarish plastic box just in front of that stupid fan relay under the headlight.

 

Built into the battery tray???
You mean it just plug onto a nipple on the batter tray?

I can tell you there is a reservoir thats under the headlamp thats rectangular there is a hose connect which goes to a "tee".

I'm just confused by what your trying to state by built into battery tray.
You mean underneath it? There's a nipple.
Please clarify. Thank you.

 

AH HAH! Crossing posts. I was going to ask you if the battery tray had a nipple on it!

 

The vacuum reservoir is plugged in.
I took the headlamp out and the reservoir goes to a T. This is a small tube.

The other part of the T goes to the actuator *not very long 1/4" hose (bigger than the other two) and is about 6 inches long.

Then the other part of that T is going over the motor.
The back of that actuatator that part of the T went T (that 1/4" hose) the back of the actuator has another vacuum hose which appears to be cruise control (going across top of valve cover).

But this hose is just laying out front under the battery cover.
I've not removed but all conenctions look ok so far. I was working on the jeep and wasn't sure if I pulled something out.

But if someone can confirm theres a hose that comes out from the battery cover for leaks etc than this would explain what the hose is and not to worry about it.

But reservoir is plugged in !
A-ok

I do suspect that actuator may be bad though for the cruise control. It just doesn't work.
Everything else does.

 

If it does maybe this hose goes to it.
IT may also explain the cruise control problem??

All other connections look good.
I havent' pulled the battery tray was waiting for a confirm on this if it plugs into battery tray..

 

There should be 3 CABLES going across the valve cover and all hook to the throttle linkage. The cable to the pedal, the cable to the transmission, and the cable to the cruise control actuator. The actuator has one vacuum hose and an electrical connector on it. It's mounted to the bottom of the battery box. The vacuum hose comes from the intake manifold and "T"s at the firewall to supply the heater control, then continues to the cruise control actuator where it "T"s again and goes to the reservoir.

 

Is it the disconnected vacuum line that goes to vent the front differential case? Check your vacuum diagram sticker... should be on top of the radiator housing with the other info.

 

No, the diff vent line is on the other side of the compartment and just terminates near the air filter box. It's just a vent, no vacuum involved, and all it does is keep water out of the diff.

 

Tracing down the vacuum leak I pulled the battery tray.
The hose is in fact on the WJ 4.0 a drain hose for the tray. IT should come out at that spot. Confirmed it is not a vacuum line. It had a kink in it so I fixed it and unplugged the drain port.

 

I pulled the battery tray. I replaced the T and some hoses that were worn.
The hose under the battery tray on my WJ 4.0 turned out to be a drain line for the tray that I did confirm. I know or guess on older jeeps there's a vacuum reservoir under there. Not on this one.

The line coming from the intake manifold went across on clips around the firewall and saw the T where a little tiny hose went through the firewall. IT then went off toward the battery tray and connect to another tee. That connected to the cruise control actuator and vacuum reservoir nicely hidden in the bumper.

I blew cigarette smoke in it and found a crack in that T so I redid the hoses and got a new tee. It's reacting better but on acceleration as opposed to slowly getting no air then a shift to defrost it does it quickly now.

So there's another leak. But I checked and the hoses and T by the reservoir are all now good. I'm pulling my hair and it all else is connected and looks good. So I'm down to thinking now it's two possibilities.

!) The vacuum reservoir itself. I have one already and might try it out.
When I tested the one in the car I took my hose just connected it to the reservoir in the bumper and sucked on it and it held a vacuum but not near as well as the new one I got does.

2) The tee junction by the firewall where this tiny hose goes into the firewall.
It might be from that point to the AC control unit?

Anyway, I'm down to these two locations everything else looked good and I repaired what I could visibly tell , including the smoke test. LOL

This one is rather aggravating to find it. But at least it's working alot better it just quickly goes from air to defrost and back again when I take foot off accelerator.

 

Reviving a 2 month old thread, eh? How was your summer? Work on the jeep much?
At this point Im not real sure what it is you are trying to fix, but, kudos on the vacuum line. As far as a drain hose for the battery tray.......well....that's a new one on me. Are you sure it isn't the diff vent hose? That's right there somewhere as Dave said earlier, as in, June.

 

Okay, for some reason my front diff vent hose has got a vent cap fitting on it's end that's clipped to the top of the front shock stud in front of the ABS module. The other end goes to a plastic fitting pressed into a hole in the front diff near the top of the housing on the back side of the cover flange. In my case, snow kept pulling the fitting out of the diff, so I put vise-grips on it and hammered on them to reseat it. Hopefully, it'll stay in this winter, otherwise I'm going to have to thread it for a brass fitting.

The battery tray drain hose was just conjecture on my part. It's good to know my thoughts were correct. I was replacing the battery on my lawn tractor at that time, LOL!

BTW, I found out why they put that fan relay under the headlight. It was an attempt to isolate it from engine heat and cool it because it gets hot itself in operation. If it's relocated on the other side of the radiator support, it will overheat.

Defrost is the default setting for the heater control if all vacuum is lost. There should be a check valve in the vacuum line near the intake manifold that seals off the line in cases of low vacuum such as in acceleration. That's when the vacuum reservoir comes into play. Just checking my FSM, there are 2 check valves in the system. The other one is in the black supply hose on the HVAC unit behind the floor vent duct. This is on non-automatic climate control units. It's supposed to hold HVAC settings during short periods of high engine load.

This Full Service Manual is the best investment I've ever made! If you've got $8 to spare, download one for your jeep from pacificcoastmanuals.com. It's 93mbs of compressed pdf files on every system in your jeep. I have learned A LOT about my WJ and WJ's in general. Another good website is wjjeeps.com

 

Yeah I went back to this problem again and wish I hadn't. Haha.
Summer was working on the jeep and getting the yard in order.
Engine wise the jeep is in great working order again.
But this vacuum leak and a seperate thread I have for the rear end on it is another matter.

What is the problem is on acceleration the AC vents move to defrost. When I stop accelerating that stops and the vents return to AC again. But it's not all the time when you accelerate . It's ONLY , and I've noticed, on an incline on the road when you have to give it more gas. Regular driving conditions the vents don't do this. So I was informed this is a vacuum leak.

Tracing all the hoses down I found a tee behind the headlight that got a crack in it. I fixed that and the hoses that were questionable and while the problem is in fact better (vents go to defrost and back to AC again much quicker) the problem still exsists. I've traced everything on this chain back the intake manifold where it goes on a nipple on it, across the firewall, then it tee's off (small tiny line) goes through firewall (I think to AC control unit) then goes down to the headlight area to another T. That T goes to the reservoir and cruise control actuator.

So this seems to be the path of the vacuum from what I see but, I'm not finding the smoking gun. It has been quite time consuming in nature, hence all summer off and on. When I get frustrated instead of wanting to get aggravated after spending days on it I typically walk away from a situation and return later. Hence the revival.....lol.

I unplugged the line at the tee where it goes into the firewall and it's got decent suction. I wouldn't say the pressure here is alot by far but it''s decent enough to stick on my arm but it will fall off. It won't make a hickey that's for sure. lol.

The line at that point that goes off to the headlight and T's again appears to be good after what I did with it. I did a mouth suction test on it and when stopped inhaling the air it wanted to take my tongue back in. So it appears that it's holding. This all maybe not the best in testing here but I'm ready to pull my hair finding whatever it is causing this vent problem.

I'm leaning torward reservoir or line that goes into firewall to AC control at this point or whatever Dave has me looking at. You mentioned this diffrential hose. I did go under the car and its plugged in it but that's on the driver side and I'm trying to trace down where that breather hose goes into?
I'm guessing this is part of the vacuum fun as well?

LOL

Thanks for helping it's been painful finding this problem.
And every mechanic I've taken it too just says, take it to dealer they can't find it or sound like they don't want to deal wtih it.

It sounds like you might be confusing my WJ 4.0 with another model of jeep? My battery tray is on the passenger side by the alternator and coolant reservoir and just behind the passenger tailiight. And there is no reservoir under the tray. It's a drain line and the hose in the picture come from a nipple underneath. My diffrential breather hose I found on the drivers side plugged in the diff (not very well either it looks like its not in there well and leaking all over it) and that hose goes somewhere. Is this part of the vacuum on the car that would case the vents to shift on acceleration like this? If so so far I can't find where the breather hose is going up to............yet.