pkt1228

I have a 98 Grand Cherokee and the air only comes out of the defrost vents. After doing some research it seemed there was a leak in one of the vacuum lines. I removed the battery and followed the line all the way around the hood and I finally found the leak. The line broke apart from whatever it was attached too and now I have no idea where it goes. I took apart the dash to see if I could find where the lines go in the firewall from the other side but cannot get a good look.
Any ideas?

thefiremeister

Did this get resolved? I'm getting ready to start looking for a leak and was looking up some info on vacuum lines.

Your problem may be my problem.

RedX

I had this same issue, I think the line goes to the vacum ball behind the bumper. If its not hooked up you'll only get air out of your defrost vents and your jeep will run like crap.

Buy 6 or 7 feet of vacume line and replace your hose.

thefiremeister

behind the bumper?? I'll have to go do some more looking.

2Evil4U

when mine did that, i capped it and ran a new vacuum hose directly off the intake to the black tube on the back of the heater controls in the dash. all fixed.

pkt1228

I took the dash off and ran a new line from the back of the **** that controls the air settings to the one under the hood. To find where it goes through the firewall I took a compressed air can and sprayed it into the black hose line inside the car and had someone listen by the hood.

thefiremeister

I checked my lines under the hood and the two little ones I see next to the heater hoses that go through the fire wall look good as far as can trace them.


if the hoses go to a can behind the bumper ( on a 1988 ) where does the vacuum originate from or where is the source of the sucking?

bfrat

I'm getting behind my dash soon. Sounds like same issue, stuck on defrost. Can you tell me size of vacuum line you ran from T joint under hood, through the fire wall? And what does it connect to on the other side? And is the connection the same size? The reason I ask is the current line is a blend of rubber/plastic, goes through firewall, and the diameter changes.

BlueRidgeMark

You are reponding to a 7 year old thread about a different vehicle.

dave1123

Okay, here's the vacuum supply routing for AFAIK all jeeps. Vacuum starts at a fitting on the intake manifold near the throttle body. They are all plastic lines with rubber connectors. The line from the intake manifold goes to the back of the engine bay on the firewall, has a "T" connection just below the hood gasket. One branch goes thru the firewall to the heater control panel, big junction plug behind the mode switch. The other branch goes to the cruise control actuator, big can with cable, and "T"s again. The last branch goes to the vacuum accumulator, either under the battery tray or behind the front bumper. There should be a check valve in the line from the intake manifold somewhere so the accumulator can close the heater doors after the engine is turned off.

It's not uncommon to break the hose to the heater when major work like an engine swap or head change is done. Likewise the accumulator is easily damaged in a collision if it's mounted behind the bumper.

bfrat, you can use any hose or lines you want to as long as the connections are made.

Vintage IRA

Just bought an 03 GC midweek. No cruise and stuck on defrost which signals a vacuum leak. Checked the lines from the manifold out around to the cruise tee( after removing the head light). Found the vacuum feed hose to the cruise control had cracks on both ends and a split midway.
Replaced and drove from the work shop home and still no cruise but the heat control now works like a champion!!!!! Guessing I may have a cracked connection at the canister. My first repair may have given the hose going thru the firewall just enough vacuum to make the heat controls work. Back to my shop to remove the battery and tray to inspect the canister connection/

dave1123

The vacuum canister is out under the right front headlight support panel just behind the bumper/fascia. It's easier to find a ball reservoir in the junkyard from something and use that. On my 37 Dodge, I used a fruit juice can with a brass pipe soldered into it for a vacuum reservoir. That car had vacuum wipers and they would stop whenever you stepped on the gas!

The reservoir's only function is to close the heater doors when you shut off the engine.

Vintage IRA

Dug in last night but still no cruise. Pulled the battery and tray (Anybody know what the little sensor/switch is in the tray?) followed the plastic hose to the Canister connect rubber hose. Like you said, disappears under the bumper cover. Had to hole saw a small hole to see the end of the hose. Replaced it with a fresh one just because I was there. Anyone know what I should see for vacuum at the cruise connection hose? Hate to whip a dead horse if vacuum is no longer the issue.

Vintage IRA

LOL here's one to watch out for guy's! On the way home from work today I tried the cruise again but again it didn't pull in when I hit the set button. Went from a 55 mph speed zone to a 45 mph zone and felt the pedal fall away from my foot and start to maintain speed! So now I started testing it with a little more patience. Turns out the speed drops off 3-5mph before the cruise begins to gently pick up speed. Once it comes up to speed it holds really well. Hopefully as I use it more it will start responding better.

dave1123

The sensor underneath the battery is a temp sensor that the PCM uses to control the alternator charge rate when the battery temp rises. It is an important devise for a proper charging system.

The cruise control will not set below 40 mph and the lower the speed it's set to will cause it to wander because of changes in the vacuum levels. If set above 60, the speed will remain more constant. It will hold a set speed better if you manually bring it up to a steady speed you want, THEN set it. Setting it while still accelerating causes it to get confused and add some speed.