Air Suspension Pressure - JeepForum.com
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post #1 of 43 Old 01-03-2016, 07:08 PM Thread Starter
JeepGC4me
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Air Suspension Pressure

Two questions,

1. Is there anywhere in the system to be able to "tap into" it to put a gauge on and see what the pressure of the system is?

2. Is there a test to be able to determine if my compressor has still got enough output on it?




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post #2 of 43 Old 01-03-2016, 07:41 PM
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I think she's pressurized to 220 psig (not absolute) so you would need the Scan tool and wiTech software to draw it down I believe to monk with it or refill it. The refill toolkit for it of course has a guage but it's like $500 new.
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post #3 of 43 Old 01-04-2016, 08:16 AM
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Please also keep in mind that QL is a "closed" system filled with nitrogen gas. You don't want to do anything that risks even a minor leak.

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post #4 of 43 Old 01-04-2016, 08:40 AM
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Yeah the system is filled with 175 psig of class 5 nearly pure nitrogen and is closed in the sense that it moves nitrogen back and forth from springs to storage tank. It will draw in air to make up for leaks, however. Pressures can reach 220 in some parts of the system. One needs a dealers type DTC to properly check and fill the system and some mass calculation expertise.

The procedures call for air suspension refill tool which is basically the typical hose, valve, regulator, and gauge you see on gas welders. I suppose if you know your way around gas welding tanks you could do it without the special tool, dunno.

You check the pressure at the storage reservoir which is under the floor panel behind the seat (tilt the seat forward for access). The fill fitting is on one side, passenger I think. Not much clearance, you will need a 90 degree quick coupler on the end of the hose.

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post #5 of 43 Old 01-05-2016, 12:12 PM Thread Starter
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According to the scan tool, there is only 65psig in the system. And it won't let me change right height with the scanner because it reports Low Air Mass. So I guess the next step is to charge the system and try to find the leak.


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post #6 of 43 Old 01-05-2016, 12:49 PM Thread Starter
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Dealer won't loan me or sell me the adapter that goes onto the reservoir. Is there an after market one that can be bought? I have 99.99% nitrogen as well as a regulator and gauge to supply 175psi to the system. And I can also perform the routines to charge each spring as the procedure calls for. Just don't have the adapter!

Once it's charged, I can monitor it to see how quickly it goes down and then start to look for leaks.


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post #7 of 43 Old 01-05-2016, 06:10 PM
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I don't recall anyone mentioning the type of quick coupler they use on the tank. Dunno if it will help to google for images for air tank quick couplers or air hose fittings and match one up with the tank. A long shot, but you could get lucky.

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post #8 of 43 Old 01-05-2016, 06:16 PM Thread Starter
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No bubbles yet. I've sprayed the shock towers, pump fittings, and valve block fittings. Nothing.

There have been times in the recent past where the compressor does run (and run and run), but nothing happens (ie: ride height does not go up). Eventually it shuts off due to overheating.

If there was a leak, and the reservoir was low (65psi) would that affect the shocks in anyway? Because they are not going lower. Ride height is staying at Normal Ride Height.

Also, if I'm understanding you correctly, there should never be a point when the system drops below 175 psi because the compressor should be able to make that up?


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post #9 of 43 Old 01-05-2016, 07:10 PM
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Looks like my edits crossed paths with your message, as it looked like you were on the right track and I was adding nothing.

The compressor can compensate for slow leaks but it cannot make up for a major leak or refill empty tanks. Air will slowly drain away as the compressor can't keep up. I believe once pressure falls below a certain threshold it stops trying.

I hear leaks can be frustrating to find. I don't have any tips for you, sorry. It looks like just putting as much pressure in as you can safely, and looking for bubbles. If your system is holding at 65 psi, perhaps its a valve body issue or a leak that only happens at higher psi. You will probably need to spray all the hoses and air bags as well as the pressure vent. I hear the most troublesome area is the fittings at the top of the front shock towers.

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post #10 of 43 Old 01-05-2016, 08:52 PM Thread Starter
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Quote:
Originally Posted by ColdCase View Post
I don't recall anyone mentioning the type of quick coupler they use on the tank. Dunno if it will help to google for images for air tank quick couplers or air hose fittings and match one up with the tank. A long shot, but you could get lucky.

Not having much luck with this. Anyone know what fitting is used to attach to the reservoir to refill the system?


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post #11 of 43 Old 01-05-2016, 10:09 PM
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Quote:
Originally Posted by JeepGC4me View Post
Not having much luck with this. Anyone know what fitting is used to attach to the reservoir to refill the system?


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Think it's this ?

http://www.handsontools.com/Miller-M..._p_111930.html
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post #12 of 43 Old 01-06-2016, 10:06 AM Thread Starter
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That doesn't look like the right part. Here is what the end of the tank looks like:



I found one kit on eBay (that has long since expired) that looks like it has the adapter needed. The adapter in the middle is the one you linked too. The one on the left is the one that has the valve on it that is detailed in the procedure. I believe the part number is 10247-2.




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post #13 of 43 Old 01-11-2016, 02:34 PM Thread Starter
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So I took it to the dealer today. They recharged the system and tested for leaks but didn't find any. What's weird is they can control each shock individually (ie: cause it to vent to atmosphere and refill) they can discharge the system completely and refill it but when they try to initiate a change of ride height (like Normal to OR1) the system doesn't go anywhere. The compressor runs, and eventually times out, but no codes are thrown. After 5 hours of them working on it I just had them recharge it and end the service visit because they seem to be out of ideas.

So $600 later, I still don't know what the problem is. They suspect electrical though but they aren't sure. This is starting to feel like the Achilles Heal of the Overland model.


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post #14 of 43 Old 01-11-2016, 04:09 PM Thread Starter
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More details to add. On the way home the compressor was kicking on every 2-1/2 minutes for about 30-40 seconds. I stopped at my mechanic and had him read the system pressure to see what the new baseline was. In Normal Ride Height, the system pressure is now at 113 psi... which surprised me because I thought it was supposed to be 175?

Does the system pressure change depending on ride height? Is there a table that shows what should be in the reservoir in Park, Normal, OR1 and OR2?

It makes me wonder if the reason the system wouldn't respond to the techs request for ride height adjustments (just compressor started to run) was because the compressor was first trying to make up the low system pressure? I hate this because I don't want to second guess the dealer, but it also cost me a lot of money and the problem is not solved.


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post #15 of 43 Old 01-11-2016, 07:39 PM
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Almost sounds like the system is disabled. The compressor should not be running that much unless you are changing levels, there is a leak, the compressor is weak, or the valve body is sticking.

According to the FSM "Using a scan tool, ride height can be changed regardless of the engine state (running or not), doors or liftgate state (open or closed). The only condition necessary is that battery voltage must be greater than 10.5 volts"

"The valve block mechanically controls the flow of air in the system and maintains the pressure in the reservoir, and in each air spring individually. Valves and solenoids in the valve body open and close to increase or reduce pressure to air lines that connect to each pressurized component allowing the system to move each corner of the vehicle up or down as necessary. All wiring connected to the valve block is directly from the Air Suspension Control Module (ASCM) which fully controls the valve body. The ASCM determines pressure from an internal pressure sensor in the valve body."

The DTC has pre-program routines to test the system. After they filled the system, they should have been able to command ride height changes. Could be a bad ASCM, but I don't recall anyone reporting that here. There have been several failed compressors.

You may want to PM Jeepcares who may be able to direct you to a dealer that knows whats going on.

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