'03 Denali air ride question

[Hacker-Pschorr]

I've been reading thread after thread trying to figure this out, my head is still spinning.

I've got two things I regularly tow. An aluminum open car hauler (usually with a car on it) or my 5,500lb camper.

With the car hauler and a 3,500lb or lighter car, everything works great. I start the truck, I hear the compressor, it levels out and I'm off.
When I shut the truck off, after some amount of time (no idea how long, I'll test if that matters) it pumps down due to the weight of the trailer. Start the engine, pumps back up, we're good to go.

With a heavier car or my camper (which isn't very heavy for a camper). Everything works fine, but after X miles down the road, the rear will drop and the compressor will pump it back up again, or at least try to but struggles to maintain level driving with what I'm assuming is close to maximum tongue weight (I doubt I'm going over with this camper).

Since it appears to be working fine until I reach a certain load, I'm at a loss as to where to start checking. This doesn't seem like the typical leak or it would do it with any load, no?

Replacing it with a standard suspension isn't an option. My other Denali (also an 03) has the air ride replaced with standard shocks / springs and I'd rather keep this one working as intended.

 

[Doubeleive]

hook up the heavy one and start spraying with a mix of soap and water and start looking for bubbles

 

[Joseph Garcia]

^^^^^x2^^^^^

 

[Hacker-Pschorr]

I had a feeling that was going to be the answer. I never found another post of someone experiencing the system working fine up to X amount of tongue weight.
I'd like to get this fixed before I pull the camper from storage. I guess I'll hitch up my car hauler and load up the tongue with weight. I should probably get one of those scale hitches and try and nail the 750lb max for this truck for the best test.

Thanks for reinforcing what I pretty much already knew but tossed a hail mary there may be another option LOL. I thought maybe if there was a check valve that supposed to "hold" the weight until it's told to pump down or something was an item to check.

 

[Doubeleive]

I had a feeling that was going to be the answer. I never found another post of someone experiencing the system working fine up to X amount of tongue weight.
I'd like to get this fixed before I pull the camper from storage. I guess I'll hitch up my car hauler and load up the tongue with weight. I should probably get one of those scale hitches and try and nail the 750lb max for this truck for the best test.

Thanks for reinforcing what I pretty much already knew but tossed a hail mary there may be another option LOL. I thought maybe if there was a check valve that supposed to "hold" the weight until it's told to pump down or something was an item to check.

you check that valve with soap&water, check the pump, air lines, both shocks. you can spray it all over won't hurt anything
if you have a tech2 you can monitor the psi but that doesn't tell you where the leak is, bubbles will

 

[nonickatall]

I had a feeling that was going to be the answer. I never found another post of someone experiencing the system working fine up to X amount of tongue weight.
I'd like to get this fixed before I pull the camper from storage. I guess I'll hitch up my car hauler and load up the tongue with weight. I should probably get one of those scale hitches and try and nail the 750lb max for this truck for the best test.

Thanks for reinforcing what I pretty much already knew but tossed a hail mary there may be another option LOL. I thought maybe if there was a check valve that supposed to "hold" the weight until it's told to pump down or something was an item to check.

I'm not familiar with the system on our cars, but I am very familiar with an airride system on a Mercedes Benz S-Class and I suspect the system is similar in function.

You have a compressor, a pressure accumulator, a valve block, a high sensor, tubes from the compressor to the accumulator and dampers.

The system works as follows:

When you start the car, the compressor comes on briefly and fills the pressure accumulator. The height sensor checks where the chassis is and the valve block either lets air from the compressor over pressure accumulator into the dampers, or lets air out of the dampers, if car is to high.

The valve block normally closed the dystem after filling or draining, so that the pressure in the dampers and the system is stable and does not act on the accumulator or the compressor.

If the height sensor changes while driving, which cannot actually happen with the same load, the system would adapt.

If your system is leaking and the pressure is slowly escaping, the rear of course lowers at some point, then the height sensor would notice that I am too low.

The valve block would try to get air to the dampers. If the pressure from the pressure accumulator is not enough, the compressor would be engaged.

If the compressor of course has to fight against a leak, or may no longer be the best itself, it may of course be that the compressor is not able to pump up the dampers properly again on a heavy load.

Since you always have the problem of moisture caused by condensation when pumping air, the compressor usually has a cartridge in which the moisture is removed from the air.

Of course, over the years this becomes saturated at some point and then the moisture gets into the compressor and into the valve block, which indicates corrosion and leaks.

So I would first look for air leaks as suggested by Doubeleive suggested. Then I would check to see if the valve block is tight. You can tell, that when you park the car, the car stays at its height for several days, because then the valves are closed. If you have checked that the line and damper are tight, the car sinks after it is switched off, your valve block is leaking.

And I would take a look at the compressor. At least at Mercedes there are repair kits for this where you can replace the piston and the seals so the Compressor delivers full performance again.

Especially when your system is leaking, the compressor is engaged to often and the wear is therefore extensive.

I might be that in our system compressor and valve are one untit, might be that our system has no accumulator. I dont know...

But the basic function and problems will be the same.

 

[Hacker-Pschorr]

I haven't had a chance to dig into this but had to tow a car this past weekend (which hasn't been an issue, only the camper). Right after the first cycle of the system, the compressor died.

Installed a new one (which came with a new pressure transducer already installed). Started up the truck, air system pumped up perfectly, a few miles down the road it sagged down and would only pump back up if I cycled the key.

I'm sure there is a leak (hope to do the soap / water test this weekend) but shouldn't the system "know" it's dropped and try to raise it again without cycling the ignition?

Also, I replaced the front shocks a few weeks ago with OEM replacements. What is the sensor for that snaps to the top of those?

 

[nonickatall]

I'm not sure how this system really works, but if I was an engineer I would have done it the same way, because normally you don't lose or gain weight while driving, so I'm guessing they check and adjust the vehicle height when starting l, but not while you are driving the car.

 

[Hacker-Pschorr]

Ok, that makes sense. I had it in my head it was always active but yea, why would it need to be?

Thanks again, I have a funny feeling I'll be ordering a set of rear shocks on Monday.