Top C Posted August 30, 2020 Share Posted August 30, 2020 I recently became aware when I accelerate in my 87 Jeep Comanche the bi-level vents switch to the defroster vent and then back after the engine speed levels out. I believe I may have a vacuum line problem somewhere but I have not found it yet. Has anyone experience this before? Also while I've got your attention does anyone know why the Vacuum reservoir bulb is mount all the way up front? I was thinking about moving it back up near the fire wall. I've done away with heater vacuum switch and all the stuff related to that switch so I have room to move it somewhere in that area. There must be a reason for that reservoir to be where it is. Thanks for your help in advance Mike Link to comment Share on other sites More sharing options...
jdog Posted August 30, 2020 Share Posted August 30, 2020 is the vacuum ball hooked up? Link to comment Share on other sites More sharing options...
Top C Posted August 31, 2020 Author Share Posted August 31, 2020 Jason Thanks yes it was all hook up. If does rain tomorrow after work I'm going to take a look at it to make nothing got disconnected. Mike Link to comment Share on other sites More sharing options...
jdog Posted August 31, 2020 Share Posted August 31, 2020 which style of ball are you using? theres a round one and a oblong one Link to comment Share on other sites More sharing options...
Top C Posted August 31, 2020 Author Share Posted August 31, 2020 Jason I have the oblong one. Does it matter? Mike Link to comment Share on other sites More sharing options...
jdog Posted September 1, 2020 Share Posted September 1, 2020 Not really if you don't have cruise or don't use it you can switch to the ball if you'd like and then you can move it from the bumper Link to comment Share on other sites More sharing options...
ComancheKid45 Posted September 1, 2020 Share Posted September 1, 2020 Check the vacuum line coming out of the firewall for cracks. Link to comment Share on other sites More sharing options...
1989commanche Posted September 1, 2020 Share Posted September 1, 2020 4 hours ago, ComancheKid45 said: Check the vacuum line coming out of the firewall for cracks. Yes this. Mine had a hole rubbed in the bottom of the hard line. Link to comment Share on other sites More sharing options...
Top C Posted September 1, 2020 Author Share Posted September 1, 2020 Thanks everyone I haven't check it yet as it's been raining pretty heavy here but I will check the lines from the firewall. Jason I don't have cruise control so I guess I'll move the canister closer to the firewall. This way I can keep an eye on the lines that run to and from it. Hopefully tomorrow I can get out there and look at it. Mike Link to comment Share on other sites More sharing options...
Top C Posted September 6, 2020 Author Share Posted September 6, 2020 Its beautiful day here got up early to do diagnostic work on the MJ. Since it was HVAC vacuum problem I dropped the Vacuum canister and check it for leaks and cracks along with vacuum lines leading from the canister back to HVAC and the vacuum motor. I found the main vacuum line was good no cracks or leaks in the canister either. I found the the line at canister going back to HVAC was leaking so I didn't have vacuum at the HVAC or the vacuum motor. Since I was going to have to run a whole new line from HVAC to the canister, I just moved the canister back to the Firewall which of course now keeps all the lines shorter. Very easy move and less likely hood of another line failure. Thanks to everyone that help me with this. Mike Link to comment Share on other sites More sharing options...
War_Pony89 Posted November 2, 2020 Share Posted November 2, 2020 Hi Joining in Late on this one. My vent only does Defrost after removing the bumper for painting I thought no big deal until yesterday when I back to far into a ditch turning around, only to realize I had no four wheel drive. So I think my vacuum has issues affecting both. checked for obvious crack signs or loose lines while flagging a tow. How is the best way to looks for cracks if they are small? Do you think I'm on the right track, both issues related or is it possible they are separate? Link to comment Share on other sites More sharing options...
MJCARENA Posted November 3, 2020 Share Posted November 3, 2020 Did you put your bumper back on? Check the vacuum reservoir and lines behind the passenger side front bumper. Link to comment Share on other sites More sharing options...
War_Pony89 Posted November 6, 2020 Share Posted November 6, 2020 Yes, never disconnected the ball zip tied it to lower fender mount. I do think there was one day it came lose and it hit my tire, but stopped right away and fixed it. I eyeballed the ball and line all the way to the intake manifold. Nothing abnormal. I think I'll have to look at it on the mcro level, since no crack or tears were obvious. If I spray some water along the line should that expose and leaks? Link to comment Share on other sites More sharing options...
jdog Posted November 7, 2020 Share Posted November 7, 2020 7 hours ago, War_Pony89 said: If I spray some water along the line should that expose and leaks? unfortunately no as its not pressure you are losing but vacuum. you will have to look, listen and inspect it all, you could also smoke test the lines Link to comment Share on other sites More sharing options...
ghetdjc320 Posted November 7, 2020 Share Posted November 7, 2020 I use a vacuum tester and check each line. Helps to find the problem right away Link to comment Share on other sites More sharing options...
cruiser54 Posted November 7, 2020 Share Posted November 7, 2020 On 11/2/2020 at 1:11 PM, War_Pony89 said: Hi Joining in Late on this one. My vent only does Defrost after removing the bumper for painting I thought no big deal until yesterday when I back to far into a ditch turning around, only to realize I had no four wheel drive. So I think my vacuum has issues affecting both. checked for obvious crack signs or loose lines while flagging a tow. How is the best way to looks for cracks if they are small? Do you think I'm on the right track, both issues related or is it possible they are separate? CAD STINKS The big issue is that the CAD system only fails when you need it the most. Kinda like when you don't realize your wiper blades need replacing until it rains.... I know somebody’s system works and he advocates keeping it stock, but my exposure to the failures is probably hundreds of times greater than his, as a result of being Service Manager at a Jeep dealership from 1980 through 1992, and being a current XJ and MJ owner. CAD stinks. Every Jeep I work on with it, I eliminate it. Guess what I find in the process? 25 year old busted vacuum lines, bloated vacuum line connectors, bad vacuum reservoirs and piping, bad transfer case vacuum switches. In other words, had the person gotten into a sticky situation and needed 4WD, they would have been screwed!!! That's the tip of the iceberg. The factory went through 3 revisions of the shift fork also. The fork issue is non-existent if you just slide it over and leave it. See the link below for complete instructions. Takes less than 1/2 hour. http://www.cherokeeforum.com/f51/fre...ss-91-a-38629/ Link to comment Share on other sites More sharing options...
War_Pony89 Posted November 9, 2020 Share Posted November 9, 2020 When I was in my pickle I definitely thought about just sliding the fork over manually. Thanks for the link and intel will research that option more.. I think I found my leak. small black tube that goes to the vacuum ball, by the battery looks like it burst the side out. Looking for that piece on-line, not finding it. Anyone know what that is called and if they sell them? Only see vacuum harness, just need that one section of 3' little tubing. Link to comment Share on other sites More sharing options...
jdog Posted November 9, 2020 Share Posted November 9, 2020 Just splice with rubber hose Link to comment Share on other sites More sharing options...
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