AHC with harsh ride (1 Viewer)

[uHu]

If you want to know the real pressure at each actuator, you will have to connect a pressure gauge. The TechStream reading is actually done at the pump. The design is such that just when the height reaches N from Lo, the pump pressure is read, once when the front level valve closes, and once when the rear level valve closes. This doesn't work for other height settings.

 

[hkeller]

uHu, did you mean from Lo to N?

 

[TXLX100]

uHu, did you mean from Lo to N?

I believe that's what he said. Going from Neutral to Low, the pump doesn't run, so the system will not update the pressure reading once the vehicle height is at the low setting.

 

[hkeller]

I must be dyslexic.

 

[ylexot]

Reviving this thread. Did anyone come up with a solution for the rough ride?


Big bumps are dreamy, but the little textures in the road get right through and rattle the interior. The roads are crumby in my neighborhood and this is driving me nuts. My wife's RX rides smoothly over these roads. My LX rode well over them when I first got it in November.

Problem seems to have started about the same time at least one of my globes crapped out. (Super bouncy under damped ride.) I replaced all 4 globes with good used globes. Reservoir went from 5 ticks to 11 and ride return to a correctly damped suspepension.

My suspension is working well otherwise. Here's what I know:
* N pressures: 6.9 F, 6.7 R
* 10 ticks in reserviore between L and H on last check
* clear difference between comfort and sport modes
* just swapped out sway bar bushings and cushions with OEM
* fresh fluid and bleed
* battery disconnect system reboot (30+ min disconnected, but didn't short disconnected positive cable to ground)

It seems like this is an issue with mechanical linkages and bushings. If so, what do I need to swap out next? What am I missing?

 

[PADDO]

Your rear pressure, at 6.7MPa, is high. Get it down closer to 6 (I'm running 5.7) and enjoy the difference. Reasons for high rear neutral pressures are:tired coils, extra weight and/or rear too high. Do the 16 step damper test to confirm damper serviceability. I worked with guy who got his rear pressure down to 6.2 with new coils and new globes yet his rear end ride was still rough. On investigation it turned out his ps rear damper assembly was stuck in hard/sport position and not responding to the ecu.

 

[ylexot]

Ooking for the instructions for the 16 step test. Sounds like a good thing to do next.

I've got a set of airbags ready to install. Im now planning on getting some fresh coils for the rear, AHC OEM coils. Also have a line on non-AHC coils with 180k miles. I'm stock weight in the back half of the rig so far, so thinking I'll just stay stock and use airbags when running heavy or towing.

(I plan on using the tbars from the same rig (180k miles) in a month or so as I now have a winch and heavier bumper in place. I was having these issues before and after the bumper and tbar crank, ie the same N pressures.)

 

[PADDO]

It's the short Ts & E1 in dlc1 test. It should identify if you have a non responsive corner, you can also measure the resistance of the step motor coils, 12-13.6 ohms between each pin to pin 2 (common return) at the dampers. Pin 2 is the centre one of the 3 pin row. Getting that neutral pressure down along with reasonable tire pressures is desirable.

 

[ylexot]

I should have some time to work on the LX today, do the 16 step test and read those resistance values. The stepper motors are in the actuators that the globes thread into, right?

 

[uHu]

Yes, that's right.

When you have 10 or 11 graduations from Lo to N, you might have e.g. 3 good globes and 1 flat, which would give a really crappy ride.

To see if the high pressure in the rear is causing a bad ride, just lower the height on the rear height sensor until the pressure is OK, then testdrive.

 

[PADDO]

I should have some time to work on the LX today, do the 16 step test and read those resistance values. The stepper motors are in the actuators that the globes thread into, right?

Yep, one motor that drives an actuator that throttles fluid between the soft damping orifice disc (the steel one) and the hard damping disc (darker one). Note the small orifice size (drilled through the shaft) at the pencil tip that controls damping.

 

[ylexot]

OK. Despite springs, spacers, and good neutral pressures, my ride is still harsh. I have been scare on time and finally delegated the 16 step test to my mechanic. The test revealed no difference in between any of the 16 steps.

Lo and behold, the system isn't working right. (it is nice to have something other than my butt in the driver's seat saying so.) The AHC goes up and down, but the Adaptive Variable Suspension part doesn't seem to be on.

He checked out the actuators. They ohmed out correctly but while stepping through the settings, he never saw any voltage over the actuator motors.

This all sounds like the system isn't on. Still no error codes.

He has performed the "input signal check" and nothing stood out as amiss. There are no warning lights, no codes, but the system appears to be disabled just the same.

With a failed 16 step test there are very brief directions to check the AHC ECM and check the wiring. He replaced the AHC ECM with a spare that I have. No difference. (I suppose it is possible that both ECMs have the same issue, but we're not convinced that a new ECM will fix the system.)

I just found the circuit schematic, so that is the next step. Is there portion of the circuit that is a likely suspect?

We are open to suggestions for what else should we look at?

 

[uHu]

Sounds very much like globes, one or more flat ones. Did you try lowering the pressure to see how it behaves? If one or more of the globes is out of gas, it could still be OK if the pressure is lower.
When bleeding the system, did you see any foaming fluid on one corner? That could indicate a punctured membrane.

 

[ylexot]

Update, the 16 step DLC1 test was pwrformwd incorrwctly the first time. Turns out, the engine has to be on, not just the ignition switch. (Makes sense, but the instructions werent clear.) The good news is the ECU and actuators appear to be working correctly. The bad news is now I'm back to square 1.

Btw, i have 11ish tick in thevreserviore going ftom low to high. The neutral pressures are 6.5 front, 5.9 rear. Cross level are all within an 1/8"of spec. No noted excessive froth from any of the bleeders.

Uhu, are you saying drop the pressures further, perhaps by moving the ride height sensors lower?

I thought the symptoms of bad globes is an underdamped suspension. Super bouncy because the system can't slew enough liquid fast enough for good damping without the compression/expansion of the nitrogen backed diapragms. They are analgous to capacitors in an electrical circuit. At least that is the story I have in my mind. Is that correct?

 

[uHu]

Btw, i have 11ish tick in the reserviore going ftom low to high. The neutral pressures are 6.5 front, 5.9 rear. Cross level are all within an 1/8"of spec. No noted excessive froth from any of the bleeders.

Uhu, are you saying drop the pressures further, perhaps by moving the ride height sensors lower?

I thought the symptoms of bad globes is an underdamped suspension.

No on lowering the pressure more. Those numbers should be OK.
Flat globes gives you a very hard suspension, hardly any movement at all. As there is no gas to compress, the (non compressible) oil (ahc fluid) has nowhere to go, and the supension is super hard. I had this, but it was difficult to detect, as those 16" wheels with 31" rubber does compress and bounce quite a bit.
It could be that you have one or two bad globes, and still 11 ticks from the gas compression in the good globes.

 

[ylexot]

Ok. Took the holiday weekend at the coast. Spent a bit of time while driving trying to wrap my head around the globes and harsh ride.

I get that flat globes would cause a harsh ride. The super bouncy underdamped ride after my globes went perhaps was due to gas in the line? Extra compressible? I had 6 ticks in the reservoir, low to high.

I replaced all 4 of those globes with used, and got up to 12ish ticks. Now, bled out, there's no more gas in the line.

What still troubles me about the globe theory is that I can manage speed bumps an larger, more gentle bumps reasonably well. I wouldn't say I float over the speed bump, but it isn't harsh.

I don't have much else to try at this point. I'm going to start shopping for globes, likely going to bite the bullet on new. I would feel better about it if I understood better though. I certainly don't want to drop a bunch of dough on new globes only to still have this issue.

 

[uHu]

I don't have much else to try at this point. I'm going to start shopping for globes, likely going to bite the bullet on new. I would feel better about it if I understood better though. I certainly don't want to drop a bunch of dough on new globes only to still have this issue.

It is a bit puzzling, not very clear cut. Understand your frustration.

 

[fumetsu]

Ok. Took the holiday weekend at the coast. Spent a bit of time while driving trying to wrap my head around the globes and harsh ride.

I get that flat globes would cause a harsh ride. The super bouncy underdamped ride after my globes went perhaps was due to gas in the line? Extra compressible? I had 6 ticks in the reservoir, low to high.

I replaced all 4 of those globes with used, and got up to 12ish ticks. Now, bled out, there's no more gas in the line.

What still troubles me about the globe theory is that I can manage speed bumps an larger, more gentle bumps reasonably well. I wouldn't say I float over the speed bump, but it isn't harsh.

I don't have much else to try at this point. I'm going to start shopping for globes, likely going to bite the bullet on new. I would feel better about it if I understood better though. I certainly don't want to drop a bunch of dough on new globes only to still have this issue.

Did you ever get this sorted out? Looking at similar problems with my rig. The AHC system is on the precipice of being deleted at this point with the amount of agony it regularly provides.

 

[ylexot]

@2002LX470, I have not figured out the underlying issue yet. So far I have (or have had done):
Set the neutral pressures to spec
Cross balance
Replaced fluid 3x
Replaced all sway bar bushings
Replaced globes with good used
Front shocks bench tested
And most recently replaced the globes with new.

With new globes the ride has improved, but the underlying harshness remains.

The 16 step test is working fine, there isn't one corner that feels more harsh than another.

Monday we are going to try swapping tires that are less stiff than mine to compare. I'm running E load rating. I'm skeptical that this is the issue as I have had these tires since the second day I bought this car, but it is easy to test when there is a spare 100 sitting around.

Failing the tires test, I'm at a bit at a loss. I'm not willing to give up the benefits of the AHC and AVS, but I can now understand the sentiment.

Will update with results from tire test next week.

 

[ylexot]

Update on tires test. I am both surprised and a bit emvarrased, but today's test clearly indicated at least some harshness is due to tires.

I have had these 10 ply, E rated Hankook AT/ms mounted for almost the whole time I've owned this rig. I remember the ride being smoother before. There was no doubt though comparing the lighter range Geolanders were smoother.

I really like these Hankooks, but now I'm going to be looking for new shoes as the next step.