MikeTheGreat26

1998 Jeep Cherokee (XJ) Sport

OK, I know this is a stupid and simple fix. I know this does not need a write up. I have been learning how to fix all the random stuff with my jeep from this blessed awesome site. Sometimes I am not familiar with names or parts or phrases for searching to get the answers I need to fix my Jeep. So I am making a post to try to help those simpletons out there. I have had to search a lot of different criteria to pull this fix from many different posts. Fear not, I have saved links with brief information on ones that have detailed info in non related posts in case anyone is interested in the sources. Now I will add one more post, hopefully helping anyone in need with the same issue. I hope this can be a go to source for helping people with their AC/Cruise control.

I hadn't noticed this issue when I lived in Chicago because Illinois is relatively flat. Moving to South Carolina, I still did not notice this issue often because only some drives I took became hilly causing MUCH HIGHER increased in the RPMs while driving at speeds above 40mph. Why does this matter you ask? It's when I notice my problem happen. Since moving the mountainous Las Vegas, NV the elevation going anywhere N, S, E, W causing even more significant fast rises in RPMs as I hold down the gas to keep up speeds.

It happens if I have the AC on and I accelerate and the RPMS kick up past 2 (2,000) or 3 (3,000) in a short period of time as in a few seconds rather than slowly accelerating over 8-10 seconds or more. You will hear and feel the AC just cut out from the front vents and blowing only out of the defrost vents even though it is on speeds of 1, 2, 3, or 4 front vent floor vent or any combo. It had been hot in Las Vegas the last 3 summers. Anyone that has been here or lived her or in this region knows AZ and southern NV get into 100's even 110-114's through the summer. Last summer I could swear we were 109-114 for two weeks straight, then for another week or two. I had what felt like no AC. I would just drive with the windows down or even up because down it felt like God was blowing a blow dryer of hot air straight into my car.

Now for cruise control. Since there are many more elevation changes from the mountains as I would go down hills and mountains and dips my cruise control works fine. Same if I am driving straight. Anytime I am doing up an incline big enough to cause the jeep to start accelerating hard on its down past the 2 (2000) RPM range and you hear that V6 fuel injected sexy engine kick in you will notice your (usually highway) speeds dropping from 75 to 70 to 65 and maybe lower. Eventually, it steadies out and hold, just at that lower speed. If I give it enough gas to get back to where I input cruise control and let off the gas it stays at the highest speed I engaged SET on the cruise control. So the only reason it drops back and holds at a lower speed has something to do with the same issue my AC is having with cutting out.

Here was my fix and potentially you simple fix too. It only took me a couple years to find and two and half HOT NO AC summers in Las Vegas and the South West.



Here are the links to the two parts you can buy along with their prices. Pictures below is the $4.99 Dorman exact fit check valve for my 98 XJ in all black. There is also a crappy universal one that didn't even work with a skinny white tip next to it showing the drastic difference in size.





Please do not use this crummy universal Dorman vacuum check valve. I got it at autozone cause they had it in stock. You are supposed to be able to blow in one end, but not the other. This is how you can test that it is working. I could not blow or suck on either end of the universal one. I did not find the exact fit valve until this one did not work. I did a little more research online and found the exact fit for $. 50 cents cheaper on amazon. Now, when I took my broken check valve out to test, I could blow in both ends. When I should it you could hear something loose inside. The new exact fit one that I got, one end sucks, the other you hear a plastic ball or fitting suck into place. BINGO. I could feel the arctic chill of my AC already in my head and I haven't even installed it yet.

It was an easy install. Check out the pictures for the exact location and what it looked like. All I did was pulled the little rubber L boot from the metal thing sticking out from the engine and then pulled on the L boot and plastic vacuum check valve from the long straight rubber boot that is closer to the firewall.









Finally, I'll make an adjacent post to this thread below with all the links I put together and saved from my searches trying to find what my issue was. In case you want actual reputable sources from veterans of this site or other Jeep sites. If you are an internet mechanic DIY different information that others conversed about along with different pictures they posted never hurts. I hope this post helps anyone due to having different words and information and citing those other sources. Maybe this post will pop up first because of the different words used in the title Good luck to anyone trying to figure this out. Hopefully it is not a more serious issue.

MikeTheGreat26

The way it is all saved, most of the quotes and paragraphs I copy and pasted from the links from peoples' posts. I post the info right below the link it was from. Some links had multiple good bits of info so there may be many paragraphs below one link. That way when I am going to my document to quickly read on what to check or buy I do not have to click the link and search for relevant information again after I researched it. Sort of a quick go to for me when I am working on my many Jeep issues. Especially since I may be researching several issues and making several different documents. Hope this is useful to all of you!

What to buy ---
http://www.moparpartswebstore.com/p/...wd=&origin=pla

http://www.jeepforum.com/forum/f11/v...valve-1065425/
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https://www.cherokeeforum.com/f2/gre...e-6558/index4/
Lots of info. just scroll down on the page for pics and information. About halfway down or further to find the vacuum pump and lines along with a lot of different types of jeeps and set ups.

http://teamcherokee.com/vacuum-reser...che-1997-2001/
"These vacuum reservoirs are all pretty much alike, but come in a single port version, like this one or a two port version which has a built in check vacuum on the source side. As long as the original is a single port it will work. Be sure to test the check valve which is somewhere else in the tubing setup. If the check valve leaks, replacing the reservoir will not help."

https://www.cherokeeforum.com/f2/c-v...e-help-236923/
*great diagram of pump location and line side and overhead view.

https://www.cherokeeforum.com/f2/hel...eration-50480/
"If the dash vents switch to the defrost only when giving it a lot of gas, then the one-way check valve for the vacuum line going to the tank in the front bumper may be toast. That was my problem. The vacuum escapes back into the intake manifold when the engine vacuum drops. Its a little round plastic valve in the tube going from the intake manifold to the firewall. Pull it out and blow through it. If there is no resistance in one direction, thats the problem. I bought a new one from Autozone for $4. I have a 1999 so hopefully its the same setup."

http://www.jeepforum.com/forum/f11/c...lerate-158984/

http://www.xjtalk.com/showthread.php?t=10555

"You DO have a vacuum system leak if your HVAC cuts to defrost when you accelerate. I don't see anywhere that you have found or fixed any such leak."

"The source vacuum from the manifold only brings vacuum to the HVAC system, the purge system and the Cruise Control (if equipped). I doubt(my opinion) if a tiny leak in one of the small pass. side hoses would cause a running or driveability problem. But it will cause the blend doors to default to defrost mode. A cracked hose, a loose connection, a tiny wear or corroded spot, especially under the battery tray where the vac lines dive down to the canister are all likely suspects."

It's fairly easy to find a vac leak on a 4.0. Blow a little smoke (and when I say smoke, I don't mean from a smoke machine, invest in a 1 cigar) into each hose...see where it comes out = leak. REPLACE any questionable lines. That'll fix your HVAC leak. If that fixes your idle problem...great, if not check the lines to your EGR solenoid.

For HVAC system there are two small tubes coming out of the firewall...one tan or pink, and one black. The tan/pink line goes to the heater control valve (if equipped). Follow the black one to the vacuum canister and/or to the cruise control...I have never seen a leaking canister unless the bumper has been hit and the can is cracked - unlikely. I relocated my canister into the engine bay and eliminated about 3 ft. of possible leaking hose.

Then start checking the lines from your valve cover. Tight grommets, elbows, fuel pressure regulator, CCV, etc. You can use the smoke system here too, but usually a visual check of the vacuum line harness near the front of the VC and the bends, elbows and fittings will do the trick. All the vacuum lines, except the moulded hard lines and pre formed harness lines are dirt cheap and well worth just buying bulk hose and a handful of fittings can be had for less than ten bucks. I even have some plastic sprinkler hose for vac lines on my MJ.

The pre formed lines, including the CCV and associated grommets can be found at NAPA in two halves for around 40 bucks. The grommets may look OK on the outside but take a look at these pics:

Here's my OLD CCV grommet, looks pretty good, eh?

"Vacuum system : If your HVAC system is stuck on defrost or changes modes under acceleration than nine times out of ten the vacuum reservoir in the front bumper is disconnected. Looks like a ball or sphere. One vacuum line going in. Thats it.
CHECK THIS ISSUE. COULD BE WHY AC CUTS OFF WHEN ACCELORATING.

There's a little vacuum reservoir in the front bumper that the line can pop off sometimes. It's the same shape and similar in size to a softball. One line going in and nothing coming out. Should be visible looking forward from the passenger front tire in the front bumper. Check there first"

https://www.cherokeeforum.com/f2/hel...eration-50480/

https://www.cherokeeforum.com/f5/hva...ncluded-49071/

https://www.cherokeeforum.com/f2/vacuum-mileage-235568/

http://www.jeepforum.com/forum/f13/v...-issue-637575/