So, I bought this thing a week ago and the SLS has been FUBAR since I picked it up (but hey, I love messing with this kinda stuff, so it didn't really concern me too much).

After looking at the RAVE diagrams and system description, I think the exhaust valve on the compressor is stuck in the closed position, preventing the system from releasing air and auto-leveling itself again.

Rarely does the system throw an SLS light, but sometimes it will. When I hit the button, she gets mad though.

Even if it's just the exhaust valve, I'm sure the compressor is probably shot too - the vehicle has 147k on it.

I like this system, and I'm not just going to give up and throw coil springs on it. I'm going to use it for towing in the future, as well as carrying heavy loads and possibly 7 passengers at some point - SLS ads another dimension of stability and safety when doing things like that.


Does anyone know the duty cycle of the factory unit, or the working pressures? I need to know the amperage rating for the compressor circuits too (the fusible link and relay for the SLS system is rated at 40A, but that's for a number of components).

I think the 4 corner RR system is 150psi, with a 20A rating - however this sytem incorporates a tank, which changes things a bit.

My next question is the exhaust valve, which is incorporated into the OE compressor. In a perfect world there would be a hot wire for the compressor and another for the dump valve - both working at 12v and "normal" current ratings.

In theory I could just use a Viair compressor (I'm thinking the 380 which has a 100% duty cycle @100psi, and 55% @200psi - which is its max rated pressure, it pulls 16A and works at 158 deg).

I could hook up a "T" fitting; 1 side from compressor, another to an aftermarket 12v air dump valve to act as the old internal exhaust valve, and the 3rd side to the OE "air control valves" for the left and right air bags.

This seems so simple (again, in theory) that I'm surprised I haven't found anything about it when searching. That compressor is ~$190 and an air valve is $20. With fittings, hardware, lines, brackets, etc I wouldn't be over $250 shipped. Land Rover NA wants ~$630 for the compressor unit, and I have a local shop that's got a new one in the box for $400, BUT this system has proven unreliable and slow in operation - I'd feel better about replacing it with stronger components if I plan on keeping the DII for a while longer.

Let me know your thoughts or if you have additional information about the OE system specs and operation.

 

Have you considered the height sensors? Or the sensors that tell the truck that it is stuck (if there are separate sensors for that)? Sounds like your truck thinks that it is stuck. I would think that if it was the compressor, the bags would go down in a couple of days. Also, there is something in there that tells the SLS unit when the truck is going over 25, I think, so you might want to check into that. Sorry to be so vague but I am not mechanically inclined... I have just been having issues with the system myself.

 

Yeah that's what leads me to think that the system can't release air pressure - it should lower itself (I think it's 18mph) and should also auto-level if I'm driving down the road or even parked, it's doing nothing right now.

In theory, good air bags won't leak. However I think I'm pushing my luck and eventually over a long enough period of time, this thing is going to start sagging (and probably not evenly!)

 

What about manually letting the air out from the compressor box and see if it does it again? You can disconnect the air hoses from either the top of the bag or at the box but I would bet it would be hard to get to the top with it jacked up like that. Maybe that will at least let it get stuck in normal operating height. (It could also cause the system to fail completely though so...)

 

Yeah exactly - I'm sure that would end up leaving me stranded knowing how my luck goes haha.

I just stuck my head under there, and I can year a loud TAP noise every few seconds! I heard this while driving yesterday for the first time, sounded like I left a screwdriver in the door compartment and it was rolling around - it HAS to be the solenoid valve trying to open.


I didn't think those things got stuck shut though? If it's making the tapping noise, SOMETHING is moving. This is so bizarre. I need to open that thing up and take a look, it's almost like the previous owner capped the lines to make it drive all jacked up haha.

 

You know nothing about the system, if you want to fix it right send me your number before you butcher up the system completely, and I'll call you.

 

Well the RAVE manual pretty clearly outlines the operation of the unit - the control valves decide where the air goes, and are fed by the compressor or exhaust valve depending on the operation commanded by the SLABS unit, which is fed information by the height sensors, wheel speed sensors (to auto-lower after 18mph) and door sensors (to prevent operation when doors are open).

Check this out - I just opened up the box, and the compressor was UNPLUGGED!

However the solenoid valves all have wires going to them before the compressor plug, so those should be good still. I'm going to take a voltmeter down there later, but the wind chill is brutal right now.

I was thinking someone filled it with air from an external compressor and unplugged the system so it couldn't dump air and leave them stranded, but who knows. The last previous owner (only had it for a few months) did some sketchy stuff to it, so who knows.

edit: Sooo, the compressor wasn't the only thing unplugged.

After trying to find the lines going into the compressor box area from the airbags, I noticed where the lines should be going into the left and right control valves - there was nothing there. At this point I'm a little confused, since the vehicle clearly has airbags and they're clearly still inflated. I traced the lines from the airbags, followed them to the BACK of the frame, then the bumper area....

...then to a freaking "t" fitting which led to a tire-type valve stem fitting that was attached to the trailer hitch chain hook-up plate. LAME.

Someone just cheaped out when their compressor took a crap, and filled it up with some outside air source. Sure enough, since the control valves were still attached, the sound I heard was the valves attempting to release the air.

Hopefully the control valves are still good - I wish the guy had unplugged them as well.

ANYWAYS there are only TWO wires going into the compressor - the exhaust valve is independent. It looks like I can leave everything alone and simply use a regular aftermarket compressor that feeds into the exhaust valve, then the control valves.

I'll keep you all updated!

 

Glad to see you are making progress. Hope it all works out