Cracking the AHC Code - Help me understand these numbers and Height Offset (1 Viewer)

[trudd]

Hey team,

I'm trying to solve for some rear AHC suspension "consistency" issues. 2010 LX w/ 90k miles. Stock rig, stock size tires (Defender 285/50/20 @ 34psi) for now. I replaced AHC globes and fluid a few months ago.

I have not messed with height sensors or Height Offset Utility yet.

Problem
About 60% of the time, it feels like the rear of my LX sits slightly too low and the ride is bumpy. The other 40% of the time, it feels like the proper LX/LC stance (butt end slightly up) and the whole rig feels much more planted to the ground and you can feel the AHC at work.

Since AHC is a dynamic system, it often happens that a ride will start out bumpy, and then at a stop light the rear end will go slightly up and ride quality improves. The inverse happens, too.


Observations
I've noticed via OBD Fusion that the Rear Driver height consistently reads 25-30mm lower than the Rear Passenger. When I've measured ground to fender, the Rear Driver is consistently 1" to 1.5" lower than Rear Passenger as well.

Here are some OBD Dashboards

This first reading is after pulling into the driveway after a few miles around town. I'd say the LX felt "planted" at this point, like you'd expect AHC to ride.

The second set of numbers is after I put the car in L and raised back to N twice (per some instructions I saw in a Height Offset Utility thread). I'd say this set of numbers is more consistent with what I see when the ride quality is harsher (IE, the LX is not planted and suspension feels bouncy).

I decided to fire up the Techstream and take a look at the AHC data. These are a little foreign to me, but I wonder if a solution to my consistency issues are in here somewhere.

Off the bat, I see that the RL Height Control Sensor is at -0.9, which matches up with the difference I'm seeing on the OBD Fusion dashboards. I'm not sure what to make of the Height Offset Utility numbers circled in red.

My gut tells me that I need slightly more AHC pressure in the rear to have more consistent ride quality. While I'm not too worried about the 1" lean between Rear Driver and Rear Passenger, it seems that messing with the RL Height Offset might help solve both problems.

Is it that simple / am I onto the right solution here?


Note: I'm not looking to arbitrarily lift the rig or cram in 35s. I just want that awesome AHC ride 100% of the time as a baseline.

 

[trudd]

@TeCKis300 wondering if you have any wisdom here

 

[TeCKis300]

Had to noodle on this. I tend to agree with your analysis and what jumps out at me is the net difference between the RL and RR.

I'm curious if you measure the fender heights from the ground, if what's being reported is consistent that RL is ~1" low.

If it is, it's not really an ACH setup or offset issue. Rather you are seeing the common 4x4 lean or sag to one side. While AHC seems to have some capacity to level left to right, my experience is that it's limited and has to average between all 4 wheels. To fix sag, you'll need to address it mechanically rather than hydraulically, or artificially with height sensors.

I would recommended a 10mm trim packer spring spacer. I've done the same on mine a few years back to address the sag - which itself is a super common issue across all tall 4x4 slinky suspensioned rigs, including the LCs.

 

[trudd]

Had to noodle on this. I tend to agree with your analysis and what jumps out at me is the net difference between the RL and RR.

View attachment 3692582

I'm curious if you measure the fender heights from the ground, if what's being reported is consistent that RL is ~1" low.

If it is, it's not really an ACH setup or offset issue. Rather you are seeing the common 4x4 lean or sag to one side. While AHC seems to have some capacity to level left to right, my experience is that it's limited and has to average between all 4 wheels. To fix sag, you'll need to address it mechanically rather than hydraulically, or artificially with height sensors.

I would recommended a 10mm trim packer spring spacer. I've done the same on mine a few years back to address the sag - which itself is a super common issue across all tall 4x4 slinky suspensioned rigs, including the LCs.

Thanks for thinking on it! Yep, RL is consistently 1” lower.

The number that jumps out to me is the RL “-0.6” Height Adjustment.

To my logic, the -0.6 HOU setting is contributing to the -0.9 sensor reading. But sounds like AHC has its own logic.

Guess this should be easy enough to test before adding a spacer.