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Discussion Starter · #1 · (Edited)
I found this pretty interesting. Left is QX80 with 120k miles. Right is QX80 with 120 miles. Both cars parked at the same time about 24 hours ago.

Left lost all air pressure and it is sitting on coil springs. Its getting worse over several months. When I start the car it comes back to its proud, muscular stance but after 24 hours looks weak again.

Pretty easy to see the air suspension is ready for replacement. I already knew that and priced all in. $500 for 2 OEM shocks with miscellaneous hardware (always replace mounts at the same time), $450 for compressor (if OEM) or $250 (if cheap Ebay one).

And one note for those with less miles. Most of the time it is the compressor that fails first. I talked to technicians and they said this is the most common problem. So if you have this problem and shocks are not ready for replacement start with that. Mine has 120k miles and shocks are still in great shape. However shocks are designed to 100k miles and probably sooner than later the rubber airbag that continuously roll up and down as you drive will develop microcracks that will seep air.

I plan on doing this all in the spring so will post few tips...
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Discussion Starter · #2 · (Edited)
Sagging is fixed and it was way cheaper than I expected!

Below is a pretty comprehensive write up. If you can turn a wrench, you can do this job and save $$$’s in the process.

I became desperate in the last month as my old, proven QX80, was turning into low rider every morning. I decided to do some basic diagnostics. I had to use a Nissan/Infiniti dedicated OBDII to connect to the suspension control module and it did find an air suspension code. The BlueDriver, as always, is useless for this type of situation.

I started with soapy water and spray. There are three possible group of components and their connection points:

  • Airline hoses – easy to check for leaks with spryer but highly unlikely they would leak. Airlines don’t leak unless damaged or rubbed. So of course, nothing there.
  • Shock absorber rubber bellows – difficult to check and unlikely they would leak. If so, they would typically leak at the lobe area which constantly rolls as the shock gets extended/compressed. Not easy to check and no easy to access all around the shocks but I sprayed anyway and found nothing there.
  • Air compressor – impossible to check and very likely this was a culprit of my problem. The compressor is protected by the rubber shield/cover so no access to spray or to inspect anything. Most likely leak would be internal and this type of leak is very difficult to find.
  • I check all connection points between all components and no leaks there
After reading a lot about these air compressors I realized that this needs to be my starting point. The QX80 compressor is sitting in possibly the worst place of the vehicle and this becomes an issue especially in the winter. When it runs as you drive, it sucks moist, salty air, which always circulates under the body, and that, over time, promotes internal compressor corrosion that eventually drives leaks.

I placed an order at some random (cheapest) online Infiniti dealership for a new OEM compressor ($350 with shipping). Then they cancelled my order and responded its on backorder. I placed two more orders with two other dealerships with the same effect and response. I called one and they told me its on back order for a few months now and no ETA. So, I became desperate even more.

I read that some had good success with units from Amazon so I ordered one for $300. Obviously, those are not OEM compressors, no Infinity warranty or anything like this. One big difference however is that the “Amazon compressor” comes with everything. It is mounted on the bracket, has rubber shield already clipped to the bracket, obviously all new mounts as it mounted on the bracket and comes with new inlet plug. Its truly plug and play. Just mount on the frame and make all connections. I didn’t order any of these parts from Infiniti when I was ordering an OEM compressor and this would be a big mistake as all this hardware was completely deteriorated especially mounts and mount bolts that were completely rusted out. Trying to disassembly and re-use all these rusty parts would make it pretty difficult. If you add all this hardware to the OEM compressor the total would be around $450+. When the “Amazon compressor” arrived, it was shocking how identical it was to the old Infiniti one. So honestly, I am very surprised with the build quality of this compressor. Durability and reliability? Only time will tell….

Below is the procedure to get the job done:

  • Park on the flat surface, let the compressor run and measure distance from the ground to rear wheel arches. Mine were 34 3/4 “ and 35” driver and passenger wheel respectively. This will give you some baseline to check against when you install a new unit.
  • Remove the spare tire/wheel. You have to do it unless you have a hoist. You will not be able to pull the electrical connection apart (this was the toughest part from this whole job). The good news is that you don’t need to lift vehicle at all. Once you remove the spare tire you will have plenty of room. Wash underneath of the vehicle. This is optional but should be worth every minute you spend on this, especially when you get all the dirt and salt getting into your eyes when you lay down under the vehicle fighting the electrical connector.
  • Break loose 4 bolts mounting the compressor bracket to the frame. Remove 3 bolts. Keep one there until you finish steps 4-6. The compressor will not fall on the ground when you remove the last one as it has two hangers (highlighted in yellow circles on the photo). This is a big improvement over the old Armada/QX56 design that had no hangers, especially painful at time when you install a new one. I had one bolt that was really stuck and I was concerned it would snap. This is why you want to start with this step. If the bolt snaps you still have a car with compressor to drive to your hardware store to pick up bolt extractors. Having said that even if one snaps this is not a big deal. You have 3 more left there. Nissan overdesigned that one.
  • Remove airline hoses – the objective is to push orange/red connector towards the compressor (axially forward) and pull the airline hose aft to remove it. Mark one hose with masking tape and remember which was that was. Or take a photo. The best way to remove the hose is to take a flat open wrench (either 9 or 10 mm), place on the hose, push the orange connector while you pull the air hose out. This is easy. Just note that the compressed air will escape from the first hose connection you pull. Depending how good job you did when washed your car there could be a lot of dirt in your eyes or only limited amount. Cover air hose ends with masking tape to prevent dust/dirt getting on the ends where they get into the new compressor.
  • Remove inlet hose from the connector attached to the frame. Just tug, pull and twist. The inlet valve will stay in the frame. I really wanted to remove it but there is no easy way. The only way would to hammer it in so it falls inside the frame. And then you can easily put a new one in. But I think the old valve will rattle in the frame forever. I am still debating on this one if I should do it or not. Next time I will lift the vehicle I will consider doing it if I can be sure I can fish out the old one out. This doesn’t really affect any of the remaining steps as you can easily pull the inlet hose later.
  • Remove the electrical connection. This was a real pain in my case. What happened was, over time, there was a lot of dirt that got into this connection. All this dirt was caked there and resulted in absolutely zero play to wiggle it out. Pressing the tab and wiggling it didn’t work. Remove harness from the compressor bracket by pushing two black clips with needle nose pliers. This will give you more room to maneuver. I ended destroying connector on the compressor side. Just taking a flat head screwdriver and ripping the pocket where the tab from vehicle harness connector sits. I used another flat head screw driver to pry them apart. Some minor damage to vehicle connector occurred. Looking at this now I would use a larger blade separator. Overall, very poor design/poor mounting orientation of the connector allowing to collect debris in the worst possible spot. But once you make a decision to rip the compressor connector it goes fast.
  • Remove last bracket bolt and lift the compressor out of the two slots.
  • Install in reverse order. Hang new compressor on the hanger slots, put 4 bolts and torque them down to 17Nm and connect electrical harness. For this one I would definitely recommend to put silicone grease on the male connector shoulder where it connects to an orange silicone gasket in the female connector. This is to prevent water intrusion and corrosion over time. Again, this is a bad design that has a backside of the connector with open end allowing water and dirt to collect and accumulate. Then connect air hoses by simply pushing them in.
  • Let the compressor run and complete final checks of you work. Measure distance to wheel arches. Mine was up 1/2 inch over the baseline. 35 ¼ and 35 ½ respectively. I attribute this to the old compressor unable to hold the proper pressure to keep proper height of the rear of the vehicle. Just looking at the vehicle it looks very good and proportional but honestly there is no way to tell ½ inch difference in height. I have been driving for over w week now and it very unusual how quiet this compressor is. I cannot hear it at all unless I open the window. It’s basically the same quiet as on my new QX80. The old one was really loud. The biggest test was obviously the leak test. I left the car for 3 days. It lost zero height. Zero!
So the bottom line is that it was just a compressor that just got bad and had to be replaced. 9 years, 120k miles in the worst possible environment is actually not bad at all. The cost was $300 and 3 hours of my time. With this write up you can do it in easily in less than 2 hours. And just to reference someone on this forum said the dealership charged ~$950 for this job.

Compressor bracket to frame mounting.
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New compressor installed.

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Electrical connection...hidden behind black bracket with two plastic clips that you need to remove before you tackle the job of separating connectors.
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Old compressor with rubber shield removed.

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Discussion Starter · #4 ·
This is a very good question. I measured the new QX80 and it is 34 3/4 inch on both rear wheels. My old one has about 1/2 inch more.

Having said this the air compressor replacement does not affect the preset nominal ride height. The only time you will need to set a ride height is when you replace the air levelizer control module or put a new height sensor.

You can adjust the rear ride nominal height in a simple way. Lift the tab from the right side (shown with the yellow arrow) with a flat head screwdriver. Pull the adjuster (black plastic piece with two adjustment nuts) from the sensor arm (ugly rust piece) and turn the plastic piece either extending (higher ride height) or reducing length (lower ride height) and obviously moving lock nuts out of the way and then tightening them up against the plastic pieces.

Basically the sensor measures angle change from a preset nominal height. Once the height changes by more than 15mm the air levelizer control module activates either compressor to increase pressure or exhaust solenoid to reduce the pressure. If you look at this picture and think about that this is a nominal height, extending the adjuster up will change the lever angle and the levelizer control module will activate the compressor to increase pressure in shocks air chambers to achieve proper angle as preset for the nominal height.

Finally setting a ride height (i.e. when you change the ride sensor) will require Nissan Consult so trip to the dealer would be required. I will try to play with my OBDII to see if I have this option but this would be hard to figure out without a good manual.

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Discussion Starter · #5 ·
Actually, there is a pretty good function to test the compressor. You will need a dedicated Nissan/Infiniti OBD2 scanner that can communicate with all vehicle modules. In E-SUS module you will find a lot of data and functions to test the compressor. In Live Data menu the VHCL HT CNVSN VL parameter indicates the delta from the nominal height. Once the compressor runs it should stop around 0 mm. I got +1 or -1 mm after running few tests. Starting from the nominal height you can activate the exhaust solenoid. One activation should drop height by 10mm and should not activate the compressor. Second activation should drop another 10 mm exceeding the threshold of 15 mm and the compressor should activate. It should not run more than 30-40 sec to get to the nominal position. (Note: you will need to get out of the E-SUS live data menu…for some reason the compressor would not activate when I was in that menu). Using these functions, you can check if the compressor can even achieve the nominal position, how quickly it gets there and how quickly it loses the pressure/height. I wish I knew that before I removed the old compressor so I could plot that and compare to the new one…better to learn late than never, I guess…

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