Has my 93 4.0L got weird vacuum line plumbing? Can't find where it goes thru firewall - JeepForum.com
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post #1 of 2 Old 01-30-2012, 04:44 AM Thread Starter
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2002 WJ 
Join Date: Apr 2007
Location: UK
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Has my 93 4.0L got weird vacuum line plumbing? Can't find where it goes thru firewall

I'm trying to trace a vacuum leak that's causing problems with my climate control. I've found the correct vacuum line as per the routing diagram inside the engine bay (it says it supplies climate control, cruise control and 4x4 axle), but the weird thing is that it doesn't branch off through the firewall. The line just comes up off the manifold, where there's a check valve, and then it goes over to the other side of the engine bay and into the cruise control and the vacuum reservoir under the battery.

It doesn't branch off through the firewall at any point, and I can't see any obvious empty holes in the firewall for it go through anyway. The only clue is that where the line is running about level with where the climate control unit inside the cabin is, there's a capped-off junction.

Any ideas? Does the 1993 use some weird vacuum hose routing where it's not obvious how the line gets through the firewall?

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post #2 of 2 Old 01-30-2012, 05:25 AM
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1994 ZJ 
Join Date: Aug 2011
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Some info HERE

From another post...

"You likely have a vacuum leak. Trace the vacuum line from the cruise control in the engine bay and look for broken/disconnected lines and connections. Start at the cruise control module on the passenger side of the engine bay, and work back. It's vacuum line will go to a T-connection along side the fender, that t-connection goes forward to the vacuum storage box for the cruise under the battery tray, and back around the coolant overflow tank to another t-connection next to the firewall just to the passenger side of the engine. Trace all the lines and connections that t-off the line that feeds the cruise as well until you get to the intake manifold. Also check all the vacuum nipples on the intake manifold to make sure they aren't leaking. A couple are not used from the factory and have rubber caps on them that become brittle and break over time. Check all the hard lines, t-connectors and vacuum nipples for cracks and check the soft lines as well. Check the vacuum storage box under the battery and make sure it isn't cracked/broken either.

My cruise has stopped working a few times, and it has always been because a vacuum connection has come disconnected somewhere. Usually the first t-connection next to the fender directly off the cruise module, or the t-connection on the firewall on the passenger side of the engine. Sometimes it is because I dis-lodged them working in the engine bay and sometimes they have just come loose on their own. "
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