So now suggest follow the sequence set out in Post #9 in this thread and repeated below -- this now includes comments and also answers to your questions:
1. Check that vehicle vehicle is on level ground (not in the street), wheels straight ahead, fuel full, no poorly distributed loads,
If this is OK, nothing to do here. If not, suggest find a more suitable location and re-check tape measurements and Techstream readings.
2. Check condition of Height Control Sensors – all should be close to zero +/- 5 millimetres or +/- 0.2 inches (AHC system cannot work correctly with faulty or incorrectly adjusted Height Control Sensors – absence of a DTC does not provide assurance of healthy Sensors),
If there is no reason to suspect Height Control Sensor problems -- such as erratic or inconsistent height behaviour at different times -- then assume Height Control Sensors and circuits are good, at least for now, and assume that there is no immediate need to investigate Height Control Sensors as described at Post #17 and Post #22 in this thread.
Techstream Height Control Sensor readings at Post #3 in this thread look reasonable -- a little low on the Front Left at negative 0.4 inches, likely because the Front Left hub-to-fender at 19.5 inches by tape-measure is physically a little lower than Front Right at 19.75 inches. This is reasonable. Some would say further tweaking is not worthwhile so leave it alone. Others would say tweak a little using the attached ‘cross levelling’ procedure and torsion bar adjusters with engine OFF to better equalise hub-to-fender measurements.
This also is likely to bring the Techstream Height Control Sensor readings closer to each other and closer to zero.
With Front Left a little low, the diagonally opposite Rear Right hub-to-fender tape-measurement is a little higher than Rear Right. This is as expected on a perfect chassis and perfectly attached body -- may be a matter of luck on an older vehicle. Tweaking the Front ‘cross level’ also is likely to adjust the Rear hub-to fender tape-measurements favourably.
3. Check/adjust/equalise Front ‘cross-level’ with torsion bar adjusters -- measured by tape-measure, engine and AHC “OFF”, then,
Your call. As mentioned above, tweak these a little if you wish to equalise Front hub-to-fender tape-measurements more precisely.
4. Check ‘ride heights’ at N height, measuring hub-to-fender by tape-measure – engine “OFF”, ignition “ON”, adjust if necessary using adjustment procedure and Height Sensor Control adjusters (not torsion bar adjusters), then,
Use IH8MUD recommendations by long time AHC guru @PADDO for a stock vehicle -- Front 19.75 inches, Rear 20.50 inches at N height setting. The well-known and widely respected @2001LC suggests that Front is better left at 19.50 inches at N height setting. Whatever, the idea is to make the Front hub-to-fender tape measurements as equal as practicable. Note that these ideas are not FSM numbers but are the widely used and reliable approximations of the much more fiddly-to-measure FSM height specifications.
In answer to your questions, note also that upgraded springs (or torsion bars) with a higher spring rate (such as KING KTRS-79 coil springs) do not increase the ‘ride height’ of the vehicle. ‘Ride height’ is controlled by the Height Control Sensors and the Suspension ECU. When upgraded Rear coil springs are used, the ‘ride height’ is not increased and remains the same as set at N height. Instead, the Rear AHC pressure is reduced, meaning that a higher share of the vehicle weight is carried by the springs, and a lesser share is carried by the AHC ‘shock absorbers’ -- which actually are weight-bearing hydraulic struts on an AHC-equipped vehicle. The advantage of the upgraded Rear coil springs is that they allow increased load carrying capacity while also keeping the Rear AHC pressures within the FSM-specified range and providing better 'ride comfort' in loaded conditions or if carrying permanent additional fittings. The ride will feel slightly firmer, but not unacceptable, when the vehicle is empty or if permanent fittings are removed. (Personally, I am very happy with the ride comfort and better road-holding with the KING KTRS-79 Rear coil springs especially when loaded for long distance travel -- no regrets).
To reduce Rear ‘ride height’ (and also reduce the Rear AHC pressure which is too high in the screenshot at Post #3, so therefore less damping and rougher ride), move the Rear Height Control Sensor adjuster down the slide. Suggest experiment with this, say one-eighth of an inch at a time. This will make a large difference in Rear height, maybe three-quarters of an inch. Strongly recommend that any such adjustments are made with the engine (and therefore AHC) OFF and with vehicle stands also in position under the chassis rails to prevent any possibility of the vehicle body inadvertently coming into contact with the human body if a mistake is made. After adjustment, start the engine and measure the effect. Fine tuning may be necessary after a drive around the block.
NOTE: Posts by @2001LC usually recommend minimum rake (Front lower than Rear) of 3/4 inch.
View attachment 3289652
View attachment 3289653
5. Check AHC pressures by Techstream at N height after N > LO > N movement (allow 30 seconds after green AHC dashboard light stops blinking after arriving at
N), then record Techstream results for Front, Rear, Height Control Accumulator, then,
When Front and Rear ‘ride heights’ are where you want them to be, use Techstream to measure AHC pressures -- Front, Rear and Height Control Accumulator.
6. If AHC pressures are out of the FSM-specified ranges, then (i) use Front torsion bar adjusters to vary the share of Front vehicle weight carried by torsion bars and the share of Front vehicle weight carried by Front AHC system, thereby adjusting Front AHC pressures, and, (ii) consider spacers or replacement/upgrade of Rear coil springs to vary the share of Rear vehicle weight carried by springs and the share of Rear vehicle weight carried by Rear AHC system, thereby adjusting Rear AHC pressures. (Note: Front AHC and Rear AHC are not hydraulically connected but changing the Front and Rear weight distributions may cause some small interactions between Front and Rear AHC pressures and some ‘fine tuning’ may be required), then,
After adjusting load share between springs / torsion bars and AHC system, especially at Rear, to achieve best damping characteristics, smooth travel over bumps and good ride comfort -- fine tune as necessary.
7. When heights and AHC Front AHC and Rear AHC pressures are correct, check overall ‘globe’ condition by observing the
difference in AHC Fluid level at AHC Tank between
HI and
LO heights. Per FSM, difference of around 14 graduations means ‘globes’ are near new; when the difference has declined to around 7 graduations, replace all four (4) ‘globes’. Results of this test at incorrect AHC pressures are not comparable with FSM numbers.
This test is the last test in the AHC adjustment/test sequence, conducted when heights and pressures are correct. Current difference reported is ~9 graduations. If done at FSM-specified AHC pressures, this would indicate that 'globes' are in fair condition, although there will be some loss of damping and ride comfort.
Note that AHC Front and Rear pressures, correct or otherwise, tell nothing about the overall condition of the 'globes'.
