vacuum leak/cruise control/check valve issue - JeepForum.com
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post #1 of 15 Old 11-25-2008, 06:13 PM Thread Starter
YJDuff
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vacuum leak/cruise control/check valve issue

So, I've been trying to solve a mystery. I realize I have a vacuum leak or a problem with the system. The air has been coming out of the window vents and the cruise control naturally doesn't work. I've looked all over the engine compartment for leaks. I disconnected the one way check valve and put the two hoses together and that made the vents work properly. I went to Napa and bought a new one way valve, then put it in both ways and it didn't change the vents from defrost. Does anybody have any ideas of what it might be or suggestions? Any feedback is greatly appreciated!

Thanks!
David


"Life is a garden, dig it!"
02' 4.0 WJ
2" bb lift
245/75/16 Goodyear MT/R
Rusty's Tow Hooks

Last edited by YJDuff; 11-26-2008 at 10:20 AM.
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post #2 of 15 Old 11-25-2008, 06:32 PM
TallyZJ
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Believe it or not I just posted in a thread about this two days ago.

The problem is likely in a vacuum line that resides beneath your battery tray. Its a relatively large diameter rubber hose (about 3/8" thick) and should be visible coming from under and behind your battery tray and traveling towards the passenger inner fender towards the fuse relay center. This line will join a hard plastic line that continues along the upper inner fender well to the firewall. Your cruise control vacuum solenoid will have a small and short section of vacuum line that goes from the cruise solenoid to the vacuum supply hard line. This will help you locate the main hard line so you can follow it down and under the battery tray.

The rubber line under the battery tray slips onto a plastic nipple on the vacuum storage cannister (which is actually built into the bottom of the battery tray).

The line could be split or just off. Or, the vacuum storage compartment may be split.

1996 Jeep Grand Cherokee Laredo 4x4 - 4.0L

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post #3 of 15 Old 11-25-2008, 08:01 PM Thread Starter
YJDuff
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I checked under the tray and followed it around. It's connected and doesn't appear to have a split. I also pointed out the valve that I replaced. When I take the valve out and just let the 2 hoses suction together it works. Could it be that the new valve is bad or still possibly a leak? Thanks for the quick reply.




"Life is a garden, dig it!"
02' 4.0 WJ
2" bb lift
245/75/16 Goodyear MT/R
Rusty's Tow Hooks
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post #4 of 15 Old 11-29-2008, 06:51 PM Thread Starter
YJDuff
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I've been doing some more searching for the vacuum leak. Probably a dumb question, but looking at these pictures, could this cracked rubber grommet be part of the problem? Any feedback will be greatly appreciated. Thanks!


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"Life is a garden, dig it!"
02' 4.0 WJ
2" bb lift
245/75/16 Goodyear MT/R
Rusty's Tow Hooks
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post #5 of 15 Old 11-29-2008, 08:18 PM
indept
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By the looks of it that's NOT a grommet, it's a piece of vacuum hose & that could be the problem.

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post #6 of 15 Old 11-29-2008, 09:00 PM Thread Starter
YJDuff
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My bad...I meant vacuum hose. It's the hose that goes from the back of the valve cover (pcv side?) to the intake manifold. When I take it off it seems to have some oil between the flexible portion and the hard plastic that runs through the hose. Probably another dumb question: Is that also part of the vacuum system and is it ok to have some oil in that location? It looks like I'll take another trip to Autozone and replace the cracked piece to rule that out as a possible issue. Thanks again with the prompt response. You guys are awesome!

"Life is a garden, dig it!"
02' 4.0 WJ
2" bb lift
245/75/16 Goodyear MT/R
Rusty's Tow Hooks
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post #7 of 15 Old 12-08-2008, 10:43 PM Thread Starter
YJDuff
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Finally figured it out...A few months ago I replaced the fan relay under the passenger side head light. Well when I cut the hole with my Dremel, I glazed the top of a little black box below the relay. I didn't think it was very important at the time, well it turns out that the black box is the vacuum box. The cut was just enough to go through the plastic... FYI, be careful when you cut the hole in the plastic for the fan relay. I just used some JB weld and know it is all patched up and working!

"Life is a garden, dig it!"
02' 4.0 WJ
2" bb lift
245/75/16 Goodyear MT/R
Rusty's Tow Hooks
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post #8 of 15 Old 02-17-2014, 06:27 PM
patnewk76
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Quote:
Originally Posted by YJDuff View Post
I checked under the tray and followed it around. It's connected and doesn't appear to have a split. I also pointed out the valve that I replaced. When I take the valve out and just let the 2 hoses suction together it works. Could it be that the new valve is bad or still possibly a leak? Thanks for the quick reply.



? on a pic....the one w/the 3 vacuum lines on the intake. what's the one on the left side go too. mine's missing and can't locate it. thanks

91 YJ "Tonka" 4.0/ax15, stock/stock axles,
99 WJ 4.0 work in progress
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post #9 of 15 Old 03-07-2018, 04:11 PM
PaulTL
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Sorry to bring this thread up, but does anyone know what the OEM part number is for the check valve pointed out above for an '04 Cherokee 4.0L. I tried purchasing a universal Dorman (claimed to work with the '04 Jeep), but made my defroster vents permanently stuck on.
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post #10 of 15 Old 03-08-2018, 07:17 AM
stevo_96ZJ
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the universal one should work just fine as that is what i have. one item not called out yet that was my problem was the plastic hard vacuum line it self. I searched all over for my leak just to find out that it was a ton of small leaks in the hard plastic vacuum line joints. not where the rubber hose connects to the hard line but the Tees built into the part. I took it off and put it underwater with all the ends capped but one and blew into it. bubbles came from every connection. I replaced all the lines with new rubber ones and threw the plastic out. tested with a vacuum pump and gauge and no more leaks. took less than an hour with a few feet of a couple different hose sizes and 2 packs of Tee fittings of varying sizes but now I have all new vacuum lines and my vents/cruise control works. the cost of the hose and fittings are minimal.

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post #11 of 15 Old 03-08-2018, 12:29 PM
PaulTL
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which universal check valve did you use? The Dorman has different size connectors requiring a custom solution, which may or may not have contributed to permanently sticking the defroster vents. I will check the hard lines as well.
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post #12 of 15 Old 03-08-2018, 05:56 PM
kg6mov
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If the check valve was backwards it would cause the vents to default to defrost.
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post #13 of 15 Old 03-09-2018, 08:37 AM
PaulTL
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The check valve itself didn't have any clear markings as to which direction it should go. I installed it both directions, both yielding the same results (air permanently blowing out of the defroster vent). I installed my original check valve back and the air was blowing back the way it was.

Here is the check valve I tried:
oreillyauto.com/detail/dorman-help--4422/hardware---fasteners-16585/check-valve---universal-17580/dorman-help-vacuum-check-valve/47149/4528381/2004/jeep/grand-cherokee?q=check+valve
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post #14 of 15 Old 07-30-2019, 03:24 PM
vbsurfa
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Hi - do you know the part # for the HVAC check valve at the T connector where it goes into the firewall to control the ac divertor switch ? I have a '99 XJ w/4.0 L engine I replaced the check valve that is right near the manifold with a Dorman product and hoses fit perfectly, but the T-connector site seems to use a smaller check valve - any advice ?
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post #15 of 15 Old 07-31-2019, 07:19 PM
jeepjames1
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need help to identify part. located vacuum leak under the battery tray behind the front right headlight mounted immediately behind the bumper. the vacuum hose is split by a "t". what part does that hose connect to after the tee. the plastic piece that the vacuum hose slides over is broken off. any ideas please help
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