AHC Time LO to N, N to HI, LO to HI (1 Viewer)

[GTV]

When you say raise time is worse are we talking 25 seconds instead of 15? Or are we talking 60-90 seconds?

I think the change out procedure is pretty straightforward if the bleeder is functional. The post from Indro Cruise was for a broken bleeder where the system pressure remains within the unit during disassembly. I think if you found yourself in that situation you could just very slowly crack the fluid connection loose. It will leak fluid and relieve pressure before it comes loose. That's essentially your bleeder. Messy and perhaps dangerous, but minimally so if done with care. He's right to urge caution with high pressure hydraulic fluid though. Thick gloves and of course eye pro are a must if you can't discharge pressure properly.

I think the system will inevitably drool out plenty of fluid and require some extensive bleeding for the HCA changeout.

I didn't even put the stopwatch on it this time but I'd guess it's somewhere around a minute or more. It feels glacially slow. I'll time it again today for data if nothing else.

My bleeders are good. Some caps or plugs for the hydraulic lines should be helpful to minimize fluid loss/mess. I'll see what I can find.

 

[GTV]

Is there another test I can do to confirm the HCA is bad before I order a replacement?

 

[IndroCruise]

To clarify a part of the discussion ....

Once the Height Control Accumulator is pressurised, the only way the contained fluid and pressure can be released is via (1) the solenoid valve, or (2) the bleeder valve.

In the case of the solenoid valve at the front of the accumulator -- it is "normally closed" and must be opened electrically by the ECU or with voltage applied by some other method before fluid can exit via the pipe joiners or ports on the accumulator -- all as described in my post to which @GTV has referred in his Post #19 in his thread. A reference is given in my same post to a pressure release method mentioned long ago by @YvesNL .

The Height Control Accumulator cannot be bled by loosening the pipes at the joiners at the ports on the device. That would just result in bleeding other parts of the AHC system -- but not including the Height Control Accumulator. Were this not the case, the Height Control Accumulator volume and pressure would not be controllable -- with the bleeder closed, the AHC Fluid would simply return fluid through the pipes to the AHC Tank -- obviously not intended.

It is worth reviewing the hydraulic circuit diagrams on the last four pages of the well-known attachment at the end of this Post as a refresher on what happens hydraulically in various conditions.

Removal of the Height Control Accumulator is not hazardous with the usual precautions for a dealing with a high pressure hydraulic device -- in much the same way as removal of 'globes' on LX470 and LC100 (where fitted).

Relieving Height Control Accumulator pressure via the bleeder valve is a basic step for safety -- which @GTV is able to do in his case.

For others, a stuck bleeder valve is a big problem, potentially hazardous if removal of the stuck bleeder is attempted. This is not easily resolved. However, this does not prevent cautious removal with appropriate personal safety protections of the entire Height Control Accumulator as a whole closed unit with the solenoid valve and bleeder valve intact and undisturbed.

Extraction of the stuck bleeder then can be considered far more safely than in situ on the vehicle. This needs great attention to personal safety because, if the Height Control Accumulator has been fully re-charged as should happen at the completion of a raise, then the internal fluid pressure (and compressed nitrogen pressure behind the piston) will be very high -- sealed gas pressure at manufacture stated as 5.9Mpa plus pressure added by the AHC Pump after re-charge to give the commonly measured pressure of around 10.5Mpa. So the potential for personal injury also is high, either from escaping fluid under pressure if the bleeder screw, or anything attached to it, escapes suddenly and violently. Suggest that this extraction is best done by an experienced hydraulic workshop or by persons with hydraulic experience.

Unless rust is present or the fixings were over-tightened on installation, removal of the Height Control Accumulator should not be too difficult -- although tight access to the two bolts on the top of the chassis rail can be a PITA, similar to the bolt on top of chassis rail for the Damping Force Control Actuators.

However, this is not the problem @GTV describes.

Or at least, before replacement of the Height Control Accumulator is considered, it is worth reviewing the source of the current gas frustration as mentioned already by @suprarx7nut.

This may be as simple as trapped air -- the usual suspects are the bottom portion of the 'shock absorbers' which are never fully swept by the piston and never truly 'flushed' and/or air-polluted fluid moving backwards and forwards in the longer pipes, perhaps being trapped at the interfaces with the Control Valve Assembly or other AHC components and not fully escaping during bleeding. If the AHC Fluid is 'sludgy', of if there has been unfortunate experiences with batches of US-marketed AHC Fluid (08886-81221 in 1 litre plastic bottles) which has a reputation for forming a 'gel', then suspicions might be aroused. Air entrapment released by disconnecting the Attenuator (below the AHC Pump) has been mentioned on this Forum from time to time as a helpful step.

Or there may be a nitrogen legacy from previous 'globes' (or even current 'globes') leaking gas into the AHC Fluid with a similar reluctance to exit on bleeding, as described above.

The remedy in these situations is more bleeding followed by more bleeding followed by more bleeding -- assuming that the current 'globes' are in good condition and not themselves contributing to the problem by leaking nitrogen into the AHC Fluid -- and remembering the experience reported in this thread involving not-so-old 'globes'!!

AHC Accumulator Bleed Question

Before anybody slams me for creating yet another AHC thread, please know that I have searched for weeks and not found anything on this specific issue that I am having. History: I have a 2001 LX470 with 299K miles that the dealer replaced the front AHC globes on at 265K (12/05/2017). Around two...

forum.ih8mud.com

Towards the end of the (long!) post linked below, I suggested to another Member a “Meticulous Method” for bleeding. It is is very pedantic -- the aim is to prevent the Height Control Accumulator dispersing air-polluted AHC Fluid throughout the system by making sure that only new fresh AHC Fluid enters the Height Control Accumulator during the bleeding process, specifically at the time of re-charge after the raise, "LO" to "N":

See Post #307 at
AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-16#post-14364800

The whole post might provide a refresher on a range of AHC related topics -- but it is a long read!!

However, @GTV already has done multiple bleeds -- and has a good understanding of the AHC/TEMS system.

The point is that if there is certainty that only new fresh contaminant-free AHC Fluid has entered the Height Control Accumulator at the time of re-charge after a raise, and the Height Control Accumulator is bled first, and a gassy fluid stream emerges of about the correct volume, then it is hard to avoid writing off the Height Control Accumulator, unusual as that decision may be.

On the other hand, if new fresh contaminant-free AHC Fluid has been sent from the AHC Tank by the Pump to the Height Control Accumulator, AND, clean bubble-free fluid emerges on first bleed from the Height Control Accumulator, then suggest do not replace just yet ....

The fluid volume expected to emerge from a new Height Control Accumulator on a stock vehicle during bleeding is said to be about 300ml -- or about the volume to cause the four 'shock absorbers' to lift the vehicle by around 40mm to 50mm in a raise from "LO" to "N" -- so a guess of the internal diameter and internal cross-sectional area of the 'shock absorber' piston multiplied by (say) average 45mm lift "LO" to "N" multiplied by four 'shock absorbers' gives an idea of volume, on the assumption that the Height Control Accumulator is good for one lift -- until the Height Control Accumulator deteriorates with age, or unless the vehicle is heavy, or unless the vehicle has Height Control Sensor or harness problems elsewhere (remember the now-infamous connector BI1 in the LHS Rear quarter-panel) -- and in either case, the raise will be slower and the AHC Pump will assist earlier.

It may help to borrow the gauges and fittings from an LSPV brake testing kit of suitable pressure ranges and see what is really happening to Height Control Accumulator pressures -- particularly its minimum pressure after a raise and before re-charge by the AHC Pump (should be around 5.9MPa), and, after re-charge by the AHC Pump (should be around 10.5MPa).

So what else is possible?

The Height Control Accumulator is topical -- but it is not where I would start. Been there, done that -- installed a new Height Control Accumulator as part of a "reliability renovation" of the AHC system on a young, low-useage 2006 vehicle, only to find that it made no difference whatsoever and that the original Height Control Accumulator was OK!! (Different problem in my case -- as reported above at Post #11 in this current thread).

According to FSM there is no bladder or membrane in the Height Control Accumulator. However, failure of the seals on the internal piston IS at least theoretically possible -- especially in the presence of old, dirty, sludgy AHC fluid with less than best lubricating qualities. This seems unlikely on a relatively young, well-maintained vehicle as presented by @GTV -- but who knows -- Height Control Accumulator faults (beyond the solenoid circuit and broken bleeder valves) are rarely reported on this forum or elsewhere, maybe because they are difficult to diagnose -- and so a 'reasonable service life' is unknown.

Consistency of Height Control Accumulator pressures after re-charge following a raise, plus, recording raise times and height changes compared to FSM, may give some idea -- but as mentioned above in Post #11, long raise times can have multiple causes unrelated to Height Control Accumulator .

Personally, if convinced that bleeding had been done well enough, my next suspicion would be possible air entrainment at the AHC Pump -- either at the seals between (1) the AHC Tank and the AHC Pump, or, (2) at the seal on the tiny "driveshaft" which connects the motor and the pump, or, (3) other seals within the pump, or less likely, (4) the large O-ring which seals the outer pumpcase external to the actual pump sub-assembly itself.

The likelihood of air entrainment may increase with the age of the AHC Pump and increasing likelihood as time passes of partial blockage of the tiny Inlet strainer or the bypass strainer inside the actual AHC Pump sub-assembly. In turn, this may mean that the AHC Pump creates enough negative pressure (suction) to induce air ingress. Cavitation also may occur -- this is different to aeration -- but the niceties are unhelpful, both effects are unwanted. Both effects are noisy -- so unusual pump noise is a clue.

Again a personal view -- 15 years is a long enough life expectation for an AHC Pump and I would replace the following as part of basic upkeep of the system if original equipment is still in place.

48901-60010 – AHC Pump sub-assembly (and maybe the whole works 48910-60012 -- but this is expensive!)
90311-10001 - oil seal between AHC Pump and Motor
90301-70003 – large O-ring for AHC Pump,
90301-06012 – small O-ring for AHC Pump,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),

I would avoid used replacements of AHC Pump sub-assembly 48901-60010 of unknown provenance and condition, given the IMPEX new pump price is about USD140 delivered to USA -- why do the work and still take the risk on another "old" and almost certainly worn AHC Pump -- especially if it has been opened and reassembled incorrectly, as is so easily done?

It is possible to remove the AHC Pump sub-assembly, extract the strainers and and clean everything -- but does it make sense to re-install a 15 to 23 years old AHC Pump?

So there goes another post which is too long -- but maybe there is some information here which may help ....

 

[GTV]

Thanks again @IndroCruise, I've ordered the above list (minus the bleeders as mine are good) from Impex. Fingers crossed.

A new pump should alleviate the weird noise the old one makes when it’s cold. I wonder if the two are correlated?

 

[IndroCruise]

Thanks again @IndroCruise, I've ordered the above list (minus the bleeders as mine are good) from Impex. Fingers crossed.

A new pump should alleviate the weird noise the old one makes when it’s cold. I wonder if the two are correlated?

Late edits added on noise effects:

Cannot really comment usefully on the noise when the AHC Pump is cold -- perhaps surmise that
-- this is a symptom of the pump struggling with partially blocked strainers and sucking air through seals due to various causes as previously mentioned, or,
-- it is an effect of a worn pump with too much bypass, or,
-- it is a second-hand pump which an OP has disassembled and re-assembled incorrectly with the gearcase "notch" or "slot" on the wrong side -- which would mean that that the pump is struggling to release the pressure trapped between the gear teeth as the gears rotate and the teeth exit on the inlet side, possibly inducing cavitation, or,
-- the bolts closing the pump sub-assembly simply have been over-tightened -- which would tend to put too much vertical pressure on the gearcases and on the sides of the gears themselves, inhibiting both the bypass flow from the exiting gear teeth and reducing pump performance.

Noisy effects would accompany any of the above circumstances.

In a long thread during a roadside breakdown in Patagonia, @Moridinbg described similar symptoms. A few of us contributed various views. In his story, it appears that the culprit was a worn and/or incorrectly assembled AHC Pump. The internal surfaces of the pumpcase do look a bit rough in his pictures after dis-assembly:

RTH needed - seemingly air in AHC, car in Low, stuck in Patagonia - https://forum.ih8mud.com/threads/rth-needed-seemingly-air-in-ahc-car-in-low-stuck-in-patagonia.1300130/#post-14723989

In the @GTV case, are the AHC pressures building up as expected and in a timely way -- Front AHC, Rear AHC and Height Control Accumulator?? Any DTC's??

Getting into more detail ….

If not seen before, the threads below may be worth a read. The first one starts with a description with pictures by @BullElk, showing the removal of the AHC Pump at Posts #1 and #2 ….

AHC pump removal with pics - https://forum.ih8mud.com/threads/ahc-pump-removal-with-pics.1227554/#post-14710306

Then within the same thread above, a skim through Post #10 through Post #15 which provide more pics and explanations of the actual pump internals -- and in particular, the importance of correctly positioning the pressure-relieving “notch” or “slot” machined into one of the AHC Pump gearcases.

A few more pics by @BullElk at Post #67 and additional pics by me at Posts #69 and #70 in an earlier thread (below) show what the internals of the actual AHC Pump sub-assembly 48901-60010 look like when it is extracted from the overall assembly 48910-60012 ….

AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13401098

Finally, after some repetition of previous material, a method for extracting and cleaning the tiny strainers (two inside the AHC Pump, one inside the Return Valve) are shown in pictures at the end of this Post:

RTH needed - seemingly air in AHC, car in Low, stuck in Patagonia - https://forum.ih8mud.com/threads/rth-needed-seemingly-air-in-ahc-car-in-low-stuck-in-patagonia.1300130/#post-14725242

The conclusion?

Personal view: It is all very interesting -- but having had the ‘educational’ self-help experience of personally doing this tear-down of the AHC Pump internals once myself, when and if the need arises again, I will simply buy and install a new OEM (not second-hand) replacement AHC Pump ....