Yes, I've searched. Yes, I've read. Yes, I've downloaded diagrams. Yes, I've traced all the lines in my jeep. But NO, I still don't understand this damn system.

My idle has had a routine stumble since I've had my jeep (December). I've put all my efforts into every other area of the jeep, except the engine. Now I'm working on the most confusing system of all, the vacuum system. I have an 87 which originally had the center axle disconnect, which I replaced with a solid front axle. I removed the hard lines that go to the axle and used screws to cap the lines in the engine bay. This week I discovered that the lines that go to the charcoal canister were disconnected because of dry-rot. I also found a blue vacuum line that has one of those small disc filters on the end but its not connected to anything.

I've found plenty of diagrams but haven't found any diagrams that tie everything together. My goal is to keep enough of the vacuum system for my EGR system and environmental controls to work properly. I'm removing the A/C and I've already removed the CAD axle. What else would the vacuum be used for?

- Where is the vacuum generated? Is is the port on the manifold near the rear temp sensor?
- There's a vacuum line in the right/rear side (as you're looking into the engine) of the engine bay under the coolant resevoir. It has one of those small disc filters on the end but its not connected to anything. Should it be connected to anything else?
- What other systems use vacuum besides the EGR, PCV, and charcoal canister (I'm removing the a/c)?
- Of the lines I don't need, can I just cut and cap with vacuum line caps?

Sorry for the long, rambling email. I've been trying to sort this out for more than a week . I've downloaded the parts catalogs from xjjeeps.com and the diagrams from jeepgarage.free/fr. They do a poor job of explaining the vacuum system as a whole. Please help!

Thanks for any you can offer.

 

As far as where all the little hoses go, you'll have to keep searching.

If you need simple answers: The vacuum is generated at the intake manifold (but you probably knew that right?) and piped out thru all the hoses.
If you take one of those small propane plumbing torches, you can spray (unlit) propane gas onto the vac lines and the manifold connections like the throttle body engine block and the brake booster.
When the RPM's spike, you've found a leak.

You might want to buy a package of assorted rubber caps and plugs and cap off everything on the manifold to start, then hook one line back up at a time and track it down that way.
It's a tedious process but it will get you there.

 

"I also found a blue vacuum line that has one of those small disc filters on the end but its not connected to anything."

Thats a one way valve or a delay, not connected to anything thats a leak for sure.

 

See Post #15:

https://www.cherokeeforum.com/f2/emi...layout-137782/

 

Thanks for the tip about the propane. I know I have leaks because I've found disconnected (rotted) lines and I'm trying to find out where they go and which ones aren't needed anymore. Yup, I've got caps ready to go!

I did some more searching this morning, this time using more targeted phrases like "87 cherokee blue vacuum line" and found that the blue line is a vent for the Center Axle Disconnect that I removed. Makes sense since it is routed in the same bundle as the other CAD vacuum lines. Found that info here: https://www.cherokeeforum.com/f2/blu...36/#post108716

That's one of the pics I downloaded, and while it shows the larger lines of the system, it leaves off a ton of other smaller lines that Marcucco mentioned.

I'm going to start replacing the soft lines and removing/plugging the ones that go to the CAD and A/C systems. Then I will test for leaks like Marcucco said. Thanks all!!