Noob Vac help

Ok, I've been working on vehicles my whole life, and I am ashamed to say, I have never had to work on a vacuum system and don't even know where to start. I have a 99 XJ, it has all the tell-tale signs of having cruise, bt the cruise doesn't work. I wanna check vac before I start taking stuff apart, but I don't even know where to begin. I have the 4.0 I6, so if anyone can help out, cause I can't find any help in the haynes manual and I don't have the extra $ to buy the FSM. This is my first Jeep, so be gentle, explain it like you would to a woman, please. :helpme:

First, check to see if your vacuum canister is in place. It's a softball size black plastic ball located behind the front bumper on the passenger side. Then check to see if the vacuum lines are there and intact.

Will do, thanks. I guess from the ball it's just a matter of tracing everything down, right?

Yes, just trace. It's not at all uncommon for the ball to crack at the mounting feet, so check carefully because the damage may be hard to spot. Also where the vac. line goes beneath the battery, it can get eaten away.

Ok, crawled under, didn't see the ball. I did, however, find some hose with a screw in it to plug it. I traced it back to a t fitting going to what I suspect is the cruise module and then it follows around the firewall to the intake manifold. I haven't checked yet to see if that's the vacuum and/or if it's creating a vacuum or just pulling air.

Guess I need to get a vacuum ball?

Sounds like someone plugged the vacuum line with the screw. The vacuum canisters are pretty easy to find in a junkyard.

With the engine running, unplug the vacuum hose at the servo and see if it sucks on your fingertip

The ball is a vacuum reservoir--engine vacuum pulls air out of it, then if the engine vacuum drops the reservoir tries to refill which creates a new source of vacuum pressure in the lines. The engine produces plenty of vacuum at idle, but loses vacuum when you open the throttle blades (making it easier for the engine to draw in outside air), so the reservoir is really only used as a short-term backup to keep the vacuum systems operating until you get off the gas.

Short version of the above is just pull the hose off the CC and see if you are getting vacuum pressure.

do your climate controls work? on floor, vent, defrost etc?

ehall said:

With the engine running, unplug the vacuum hose at the servo and see if it sucks on your fingertip

The ball is a vacuum reservoir--engine vacuum pulls air out of it, then if the engine vacuum drops the reservoir tries to refill which creates a new source of vacuum pressure in the lines. The engine produces plenty of vacuum at idle, but loses vacuum when you open the throttle blades (making it easier for the engine to draw in outside air), so the reservoir is really only used as a short-term backup to keep the vacuum systems operating until you get off the gas.

Short version of the above is just pull the hose off the CC and see if you are getting vacuum pressure.

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10-4, will do

hellinthewoods said:

do your climate controls work? on floor, vent, defrost etc?

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Yes, but slowly, ie, some lag from the time i turn the nob to the time they switch, but yes, they switch.

johnnyc said:

Sounds like someone plugged the vacuum line with the screw. The vacuum canisters are pretty easy to find in a junkyard.

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I got two junk cars sitting in my driveway, a 90 cavalier with a v6 and a 94 honda, would the canisters off one of these work or do I have to have a Chrysler one?iratefla

any vacuum reservoir will function, as long as it's got enough ports for the C.C. and the HVAC.

You will need to buy a Vacuum Gauge. They are inexpensive and the best way to find a leak. According to my FSM, you need a minimum of 13 inches of mercury vacuum at the CC Servo. To test, unplug the vacuum line at the Servo and connect it to the gauge. Run the engine up to 1500rpm or better and check the vacuum.

I do have a question, when you hit the ON button, does the Cruise Control indicator light up in the gauge cluster? If it does not, the problem could be electrical in nature.

The stock Vacuum Reservoir has but a single fitting as it is at the end of the line. Stock ones have been known to crack. When chasing my CC problem, I picked up an entire inch of vacuum by coating the reservoir in fiberglass resin. Must have had a hairline crack in it. When I coated it, I had it hooked up to my vacuum brake bleeder to draw the resin into whatever crack was there. Found the leak with my gauge.

o-gauge-steamer said:

You will need to buy a Vacuum Gauge. They are inexpensive and the best way to find a leak. According to my FSM, you need a minimum of 13 inches of mercury vacuum at the CC Servo. To test, unplug the vacuum line at the Servo and connect it to the gauge. Run the engine up to 1500rpm or better and check the vacuum.

I do have a question, when you hit the ON button, does the Cruise Control indicator light up in the gauge cluster? If it does not, the problem could be electrical in nature.

The stock Vacuum Reservoir has but a single fitting as it is at the end of the line. Stock ones have been known to crack. When chasing my CC problem, I picked up an entire inch of vacuum by coating the reservoir in fiberglass resin. Must have had a hairline crack in it. When I coated it, I had it hooked up to my vacuum brake bleeder to draw the resin into whatever crack was there. Found the leak with my gauge.

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Nope, sure doesn't...I was afraid it may be. After I check vac, should I start at the steering column and work back to the servo, or the other way 'round?

vac is easy to check, put your finger on the hose. the wiring for the switches are not so easy

You will need an accurate schematic and a meter. I used a Fluke 87III DMM for testing. Remove the switches from the Steering Wheel and set up the meter to read Ohms. While pressing each switch (obviously start with the ON) read the resistance. You can do a search here for CC issues and I believe that the nominal resistance values have been posted. Any value within 10% of the nominal is acceptable.

Be advised that you will be removing the Air Bag. All appropriate precautions must be taken to ensure your personal safety. Disconnect the battery and wait for the capacitors in the system to bleed off. The Air Bag system is HOT with the key off.

The Chrysler CC System uses a scheme whereby the PCM reads the current draw of a single wire to determine what you are asking it to do, By using resistors of different values, the current is changed and the PCM deciphers that you just asked for the CC to turn on, or set, or...

97 and 98 have the same switches. 99+ are the same, but not interchangeable to the previous years. If the switches are good, then the Clock Spring will need to be verified. Again, you are going to need a good wiring diagram to help. Just follow the path until you get to the PCM.

The problem I had was that the system would arm (light comes on) but would not set. I eventually traced it to a high impeadance short to ground in the wire running from the Brake Light Switch to the Servo. Once I cut the wire and ran a new one, all was well. Point being, it is not always a straight forward solution. Heeps are strange and mysterious beasties.