One more AHC trouble thread (1 Viewer)

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Dec 7, 2017
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Guys, I've done a lot of searching, but still can't understand where the failure is.
LC 2004, with VGRS and AHC.
Couple of weeks ago I realised, that the car drives very rough. That's not my daily driver, so maybe the issue progressed longer ago and I just didn't pay attention to it.
Anyway, it drives like it has no suspension at all, you can feel each crack in the asphalt. My HJ60 with leaf springs drives better!

First of all I tried the suspension switch - changing to Sport makes it even worse, so at least the switch works :)
Checked the number of marks while going from L to H - about 12, looks like everything is fine here too.
Getting from L to N takes about 20 seconds, N to H - 15.

I took the Techstream, saw that the FR sensor was pointing to 19mm in the N position (and both FL and Rear close to 0).
Checked the pressures, nothing unexpected - front 6.5, rear was 8, but I didn't pull off the temp.sensor.
Corrected the front right sensor, everything is fine, but the ride is still rough.
Luckily I had 2.5L of AHC fluid left from the previous fluid replacement a year ago - so I've replaced the fluid like it's written by PADDO. The fluid was dirty and dark (replaced a year ago!).
Also, there was a lot of air in the pressure accumulator.

Still the same situation, did not get better at all.

I don't have the screenshot of the system after the sensor correction, just the one before - so pls ignore the 19mm, it's now -0.2mm
The front pressure is now 6.1, rear 7.5
VirtualBox_TechStream 12.20.024_06_02_2021_12_10_40-AHC before changes.png


Steering angle -146deg in the picture looks suspicious to me, because the car drives straight and the steering wheel is straight. Did the VGRS calibration several times - no change there.


Any ideas where to start from?
 

suprarx7nut

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A couple things.

1. The gradation test must be done from H to L. Not L to H. (edit, looks like I'm wrong here - L to H is in the manual.) Try that again and report back. Bad globes are a VERY common reason for a rough ride. They do not last forever. If you suspect they are 10 years or older, it's likely they are bad.

1b. Air in the accumulator (or any part of the bleed process) is a common sign of a failed globe. It's not actually air in that case, but rather the nitrogen that used to be pressurized and contained within a shock/gas chamber (globe) or the height accumulator.

2. Steering angle isn't a problem, necessarily. It's a measure of an internal gear and the degrees shown there aren't readily converted into an actual steering wheel angle.

3. How much fluid did you get out of each corner while bleeding? Very little fluid during bleeding can indicate a failed gas chamber (see note A again).


Given your info here, I'd put money on a failed gas chamber (globe).
 
Last edited:
Joined
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Well, no more puzzle, the globes need to be replaced (or maybe together with the whole suspension, or maybe with the car together).

Today's test shows 7 grades, no matter L to H or vice versa. The reason why it was 12 or more yesterday is simple: the nitrogen was still in the system, located in pressure accumulator. Yesterday I drained the system and replaced the fluid - no more nitrogen in it and only 7 marks.

For me it looks like:
- if you have 7 it's obvious that the globes are gone
- if you have 12 it's everything fine
- if you have more than 12 and the globes are old and suspicious -- drain the air/nitrogen/whatever is in there and you'll get to 7
 

suprarx7nut

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Many posts from others including @PADDO mentioned doing graduation test from L to H. What is the reason for this test must be done from H to L?
I think the manual only states h to l. Maybe I'm wrong. 🤷

Part of the reason might be that the height accumulator can empty/fill during raise so the fluid level could fluctuate. If you set it to high, wait a minute, then lower, the height accumulator should remain full during the test and will not skew results.
 

suprarx7nut

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A full set of globes is $750 via impex. Labor to install is pretty quick and easy. Don't get rid of the car over bad globes, haha.
Well, no more puzzle, the globes need to be replaced (or maybe together with the whole suspension, or maybe with the car together).

Today's test shows 7 grades, no matter L to H or vice versa. The reason why it was 12 or more yesterday is simple: the nitrogen was still in the system, located in pressure accumulator. Yesterday I drained the system and replaced the fluid - no more nitrogen in it and only 7 marks.

For me it looks like:
- if you have 7 it's obvious that the globes are gone
- if you have 12 it's everything fine
- if you have more than 12 and the globes are old and suspicious -- drain the air/nitrogen/whatever is in there and you'll get to 7
 
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Brisbane, Australia
Well, no more puzzle, the globes need to be replaced (or maybe together with the whole suspension, or maybe with the car together).

Today's test shows 7 grades, no matter L to H or vice versa. The reason why it was 12 or more yesterday is simple: the nitrogen was still in the system, located in pressure accumulator. Yesterday I drained the system and replaced the fluid - no more nitrogen in it and only 7 marks.

For me it looks like:
- if you have 7 it's obvious that the globes are gone
- if you have 12 it's everything fine
- if you have more than 12 and the globes are old and suspicious -- drain the air/nitrogen/whatever is in there and you'll get to 7

Mmmm – intuitively, at first I would have agreed to do this test from “HI” to “LO”.

However, the FSM says I would be wrong.

To further assist @imdek and @medtro and newcomers who may follow ….

For comparable standard numbers, the attached FSM extract prescribes that the HI/LO Test of overall ‘globe’ condition be done after AHC pressures have been adjusted to FSM-prescribed AHC neutral pressures at “N” (using torsion bar adjustment at front and spacers/replacement springs at rear etc).

At correct neutral pressures at “N”, start test with engine running and AHC operating by dropping from “N” to “LO” and record AHC Tank level.

Then raise to “HI”, and hold for 30 seconds with engine and AHC still running to ensure that AHC Pump has finished recharging the Height Control Accumulator (this can be heard, felt and also seen on Techstream when the solenoid valve at the front end of the Accumulator (SLAC on Techstream), has returned to its normally closed position.

Then record AHC Tank level at “HI”.

Then note the difference in graduations between “LO” and “HI” at AHC Tank – where 14+ = as new ‘globes’ and 7 = ‘globes’ in need of replacement according to FSM.

Thinking about it – it makes sense:
  • At “LO”, the Height Control Accumulator is isolated from the rest of the AHC/TEMS system because its solenoid, SLAC, at the front end of this Accumulator remains closed,

  • At “LO”, the AHC/TEMS system is at the lowest possible pressure (because more vehicle weight is taken by the torsion bars and springs than at “N”),

  • At “LO”, the pressure on the fluid side of the diaphragm (membrane) within the ‘globes’ is lowest possible and offers lowest possible resistance to the nitrogen gas pressure on the gas side of the diaphragm (membrane). In this condition, nitrogen gas pressure in the ‘globes’ will push the maximum possible fluid back to the AHC Tank,

  • At “LO”, when the ‘globes’ are completely worn out (meaning that the nitrogen has diffused or leaked as it will over a long period of time), then there will be no or very little pressure to push fluid from the ‘globes’ back to the AHC Tank. Fluid also will have leaked to the gas side of the diaphragm (membrane), ultimately filling this void with the fluid. In the end, the failed ‘globe’ is simply an inert ‘tank’ of fluid from which fluid cannot leave because there is no pressure make it do so.

  • “HI” measurement must be taken after re-charge of Height Control Accumulator is completed and its solenoid valve is closed, thereby isolating the Height Control Accumulator from the rest of the AHC/TEMS system until the ECU causes it to open for another raise later.

  • At “HI”, when the ‘globes’ are completely worn out (meaning that the nitrogen gas has diffused or leaked as it will over a long period of time), then there will be no or very little pressure and very little resistance to the AHC Pump (or the Height Control Accumulator) filling the ‘globes’. The diaphragm (membrane) either will be pushed hard against the back wall of the ‘globe’ or it may be perforated and allow fluid to fill the void formerly occupied by nitrogen gas,

  • As the ‘globes’ age and slowly deteriorate, the volume of fluid pushed back to the AHC tank by the slowly depleting nitrogen gas pressure becomes smaller and smaller,

  • The test only indicates overall ‘globe’ condition. It does not identify individual ‘globe’ failure. The 16-Step Test, corner by corner, may provide additional information. However, when one ‘globe’ fails it usually means that the others are not far behind.

Other Notes:
  • @suprarx7nut already has summarised all of this – now you have the longhand version as well!!

  • Front and Rear AHC pressures by themselves tell nothing about ‘globe’ condition,

  • Bubbles in AHC fluid often mean the presence of air in the system but also may mean that ‘globes’ are failing, that nitrogen is diffusing into AHC fluid, partially dissolving and then re-emerging as bubbles in low pressure areas around pumps and valves per Henry’s Law. [This why bubbly fluid bled from the Height Control Accumulator may indicate failing ‘globe(s)’],

  • Unless there are other faults or excess weight or air in the system, the AHC system will raise LO > N > HI in the normal way, regardless of ‘globe’ condition, using the pressure provided by the AHC Pump and the Height Control Accumulator and with the ‘shock absorber’ struts acting as simple jacks,

  • The most common cause of ‘harsh ride’ is failed ‘globes’,

  • The second most common cause of ‘harsh ride’ is the ‘fail safe condition’ caused by failed or widely different Height Control Sensors resulting in the ECU locking the active damping feature of TEMS into Step 8 of 16 Steps – can be felt at low or town speeds and can be observed real time in Techstream (with someone else driving -- look at "Front Wheel Step" and "Rear Wheel Step", if they are not varying with road conditions then the ECU has placed the system in 'fail safe mode'),
 
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For comparable standard numbers, the attached FSM extract prescribes that the HI/LO Test of overall ‘globe’ condition be done after AHC pressures have been adjusted to FSM-prescribed AHC neutral pressures at “N” (using torsion bar adjustment at front and spacers/replacement springs at rear etc).
 

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For comparable standard numbers, the attached FSM extract prescribes that the HI/LO Test of overall ‘globe’ condition be done after AHC pressures have been adjusted to FSM-prescribed AHC neutral pressures at “N” (using torsion bar adjustment at front and spacers/replacement springs at rear etc).

At correct neutral pressures at “N”, start test with engine running and AHC operating by dropping from “N” to “LO” and record AHC Tank level.

Then raise to “HI”, and hold for 30 seconds with engine and AHC still running to ensure that AHC Pump has finished recharging the Height Control Accumulator (this can be heard, felt and also seen on Techstream when the solenoid valve at the front end of the Accumulator (SLAC on Techstream), has returned to its normally closed position.

Then record AHC Tank level at “HI”.

Then note the difference in graduations between “LO” and “HI” at AHC Tank – where 14+ = as new ‘globes’ and 7 = ‘globes’ in need of replacement according to FSM.
Interesting to see Australia has a higher standard of 8 graduations or more (PDF from @IndroCruise in post #8).
 
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A short update:
1. I'm unable to unscrew the old globes. Everything is rusty and doesn't move.
2. I've tried again the graduation test (still with old globes) - get 12 graduations from H to L and vice versa.
3. Did a check with techstream. Anything suspicious here? 1.4mm is 0,05", precise enough I guess?

Still drives like a s***box :(

Btw, rear pressure is too high, despite new spings and no additional load. What could be the reason? Temp connector was disconnected, didn't change anything.
Both wheel step changes during the ride

VirtualBox_TechStream 12.20.024_20_02_2021_20_45_44-corrected.png
 
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suprarx7nut

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A short update:
1. I'm unable to unscrew the old globes. Everything is rusty and doesn't move.
2. I've tried again the graduation test (still with old globes) - get 12 graduations from H to L and vice versa.
3. Did a check with techstream. Anything suspicious here? 1.4mm is 0,05", precise enough I guess?

Still drives like a s***box :(

Btw, rear pressure is too high, despite new spings and no additional load. What could be the reason? Temp connector was disconnected, didn't change anything.
Both wheel step changes during the ride

View attachment 2591358
Are your bushings good? This might not be an AHC problem, but rather a suspension problem. Control arms front and rear, upper and lower all in good shape? Ball joints checked and good?

12 gradations should be plenty.

Have you bled fluid? If the fluid is old and broken down some folks have noted significant improvement by simply changing out the fluid. *Edit, I see you said you bled fluid.

Rear pressure seems to be a little high on lots of older vehicles. I'm not sure why. 30mm spacers will help.
 

uHu

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A short update:
1. I'm unable to unscrew the old globes. Everything is rusty and doesn't move.
2. I've tried again the graduation test (still with old globes) - get 12 graduations from H to L and vice versa.
3. Did a check with techstream. Anything suspicious here? 1.4mm is 0,05", precise enough I guess?
Still drives like a s***box :(
Btw, rear pressure is too high, despite new spings and no additional load. What could be the reason? Temp connector was disconnected, didn't change anything.
Both wheel step changes during the ride

Reason for high pressure can be that the actual height is too high. Not the sensor height which will always be around zero at N, pressures allowing. If the rear sensor is adjusted to a higher actual level than spec, the pressure will be too high. If the height is at spec, try lowering it by half an inch to see if that helps.

On the 7th, you said that you had 7 graduations. If it is back at 12 now, it might be that you have more nitrogen released. Also, it is possible to have 3 good globes and one bad (flat, solid, no movement), which could still give up to 12 grads, as it is the total fluid capacity/use/displacement in 4 globes together which is measured. How old are the globes?

If the globes are rusted on, it's time to bring out a chisel and a bfh. Do you have a good 36 mm spanner btw?
 

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