Testing air suspension for leaks?

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powershift

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Monday I woke out of my LR4 and my head hit the hatch glass when it was all the way open. I suspected the rear end dropped on both sides since I cleared the hatch the night before so that sent me on an investigation to find out if I have an air suspension leak. One thing different vs when I didn't have that issue is now I'm driving up on 2X6es to level the cargo area while in street mode so maybe that is changing the behavior of how it sits and adjusts because something definitely changed.

On Monday I saw the rear lift after starting it so that was some evidence of a leak. Then on Tuesday the problem reproduced exactly the same. At that point instead of starting I put the charger on it, went for a hike came back and it was lifted up again. I swear to God I thought maybe the thing self leveled when it knows a charger is on there.

So then I test to see if it self levels with a charger on there the next morning and it did not. I began to wonder if the glass hatch struts are getting worn out or it is a combination of things. I started taking measurements from the ground up the centerline of the wheel to the bottom of the fender trim and found that today the RR did not raise up in the AM after starting the engine.

Each time I measured the suspension I didn't do it as suggested until today and I'll need to get measurements tomorrow. What I was hearing was to put it in off-road mode, pull the fuse and come back 24hrs later. I pulled the fuse after shutting the engine off and noticed when I got out but before pulling the fuse that it made a hight adjustment. I thought about pulling the fuse before turning the engine off but then I wasn't sure if that would throw a code. To take proper measurements do you need to pull the fuse before or after shutting the engine off?

Then I took measurements while in off-road hight and discovered that the measurements change about 1/8" when I get in and out lol. It seems like it will be hard to stay out of it for 24hrs. I measured 8 hours without being inside and there was no drop, but it wasn't in off-road hight either.

I've never owned an air suspension before so this is all new and exciting to me. I looked at valve block rebuilds vs buying a valve block but I'm not confident that there is a leak or there isn't a leak. I had it checked a couple months ago and it was fine. What other evidence could I look for that would point to a leak? How much variance between measurements would be acceptable? I was using 1/16" of an inch accuracy and I'm starting to wonder if that is too narrow?
 

ryanjl

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The suspension readjusts often. When you turn the vehicle off. When you turn the vehicle on. I wouldn't use that as evidence there's a leak.

Just put it in offroad height with the fuse pulled. You can pull it before or after you turn the vehicle off. If before, it will throw a code, but the code will go away when you put the fuse back in.

If it hasn't dropped any after 8 hours you are probably okay.
 

powershift

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The workshop manual for the Vehicle Dynamic Suspension is a good read, thanks. It refers to a High Speed mode where the suspension is dropped when it detects 100 MPH. Does anyone know what year this feature was introduced?

High Speed Mode
In later software a high speed mode is introduced. High speed mode is a non-selectable, automatic mode which lowers the vehicle
height by 20 mm to improve vehicle handling. This feature is fully automated and is 'invisible' to the driver.
If the vehicle speed exceeds 100 mph (160 km/h) for more than 5 seconds, the air suspension control module initiates the high
speed mode. When the vehicle speed reduces to less than 80 mph (130 km/h) for more than 30 seconds, the vehicle returns to
'on-road' height. This function is cancelled if a trailer is connected to the trailer socket.
 

scapistron

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My old Ram would lower into aero mode at like 55mph. 100mph in something less aerodynamic than an old Volvo seems like a bad idea.
 

f1racer328

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I’m sure it’s more for stability than aerodynamics, considering our LR4’s have the same drag coefficient as a brick wall.
 

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