AHC help needed

[Kalino_74]

I hooked my 2002 LX470 with 80K miles up to techstream yesterday to see what my neutral pressure readings were after replacing my globes. I was only getting like 6 graduations from the old globes and my front suspension felt like it was stuck in sport mode. After replacing the globes I have 14 plus graduations but the truck still feels like its in sport mode.

I hooked up the techstream , lowered the truck to L then back to N and checked my pressures. This is were it gets WEIRD. These were my pressure values.

Front 3.2
Rear 6.7
Accumulator 10.4

It seems like suspension is just using the torsion bars to hold the weight of the truck. I then make sure the truck is on level ground and then I proceed to get the front driver side and passenger side level. After getting the front level 19.75 hub to fender I crank counter clockwise 7 full turns then recheck my numbers. The front pressure jumps to 10.2....what???? So I go back clockwise 2 turns at a time until I got to about 8.3. If I turn each side a 1/4 of turn it will drop back to 3.2. I don't get it...… While the truck is going from L to N it will show Front 6.7 Rear 6.7 and it will stay that way for a few seconds then when the pump stops running the rear will stay but the front drops to 3.2.

If I leave the front at say 8.5 and drive the truck it rides pretty decent but once I try to get it in spec like anything below 8.0 it just drops to 3.2 and rides like crap again.

Does anyone have any ideas? These are the things I've done

Flushed a year ago and again when I installed the new Toyota globes.
Bled the system really good twice.

 

[PADDO]

You’re getting a spurious front pressure reading. Don’t believe Techstream numbers that indicate the pump output and the systems preload pressure in the front circuit changes so significantly with just a 1/4 turn on the torsion bars. It appears that these systems can get their solenoid switching timing to pump output pressure out of sync, resulting in unrepresentative values being read into the AHC ECU. I’ve seen weird readings like this previously (posted about it) and that’s why I now use a pressure gauge, It will probably resolve after a few stop/start and drive cycles. You might try pulling the battery neg terminal (with front wheels straight) for 15 minutes to reset the AHC ECU, it certainly won’t hurt.

 

[Kalino_74]

Thanks Paddo, you were right. After taking a short trip in the truck and checking the pressures again I was able to adjust the TB's to get them in spec. The truck still drives very firm in the front for some reason. I did the 16 step damper test this morning and it rode great when I locked it down in the softer settings. After the test I shut down the truck pull my paper clip then started the truck back up and went for a test drive. It rode smooth for about a half a block then reverted back to the stiff ride. Is it possible that I might still have some nitrogen in the lines from the previous failed globes? The second time I bled the accumulators I still had some frothy pink fluid coming out but I chalked it up to the way it was coming out of the bleeder. Does the fact that it rode smooth during the damping test eliminate a problem with my damping control actuators? Thanks for you help.

 

[PADDO]

Frothy fluid indicates you’ve still got gas entrained in the system that needs to be removed. You can either bleed the complete system down via the five bleed points and carefully recycle your fluid into a clinically clean vessel (I use a very clean HD paint mixing container with a piece of clean cotton T shirt stretched across the top as a reasonable particulate filter or you can buy sheets of cloth filter material ) and tipping it back into the reservoir. You might do this a few times over a few days. Or you can do it the non invasive way and drive the vehicle down to the front and rear bump stops in the active test mode several times over a few days. Idea here is to compress the shock actuators as far as possible in situ to expel as much fluid/gas from them as possible. But even on the bump stops the shock actuators still retain quite a bit of fluid. Any steps you can take to relieve pressure and let the nitrogen gas off will help. If you’re getting smooth operation initially that suggests your damper assemblies are doing what they are supposed too. If you’ve still got gas in the system that’s heating and expanding when you drive then that’ll play havoc with the damping response.

 

[Kalino_74]

I will definitely take your advice and continue to bleed the system until all the gas bubbles are gone. I like the idea of the HD paint can and clean cotton T shirt, recycling the fluid will definitely save me some $$. I will report back once I have all the gas removed, hopefully with some good news. Thanks again for your help.

 

[Kalino_74]

Okay, so I bled the system a total of 6 times over a period of 3 days. I'm not getting any more air bubbles. My pressure in the front is at 8.4. I know this is high...... For some reason now my passenger side TB bolt will not turn CW or C. My truck is spotless underneath but I did spray with WD 40 for good measure. The driver side turns both directions with ease. I've tried putting the truck in H mode and I even lifted the front tires off the ground without success. After completing my bleeds I raise the car from L to N then go for a test ride for the first 20 ft is smooth then resorts back to being rough. Before my passenger TB issue I was able to get my pressure down to 6.9 and if I tried to get it down any further it would go to 3 for some reason. ?? If I put the truck in the 16 step mode it drives great! I know this won't work but I wish I could put it in step 1 of the 16 step mode then pull the AHC so its locked in.

I'm not sure what to do with the stuck TB. I will do some searches tonight after I take my sweetheart out for dinner. I might have a 2002 LX470 with 81K miles for sale really soon.

If anyone has any ideas I would love to hear them....

 

[trdcorolla]

Maybe your AHC switch by the transmission gear selector is bad and is always outputting the hardest setting?

 

[Kalino_74]

Maybe your AHC switch by the transmission gear selector is bad and is always outputting the hardest setting?

I can tell the selector is working but there just isn’t a lot of difference between sport and comfort. It’s almost like I need 5 more positions past comfort. I appreciate the input though.

 

[PADDO]

Can’t really have a sensible discussion regarding damping performance with a front neutral pressure of 8.4MPa.

 

[Kalino_74]

I’m ordering my new TB adjuster bolt today. I had the pressures correct but I backed off just trying to see if it made any difference then the TB bolt ended up cross threading. I’ll instal the new TB bolt get my pressure in spec and report back. Thank you

 

[Kalino_74]

Paddo,

I was reading one of your post when you stated that speed can effect dampning. I don’t have any trouble codes on my AHC but I do have three codes that related to my ABS/VSC/TRAC. One happens to be a C0210 which is the RR wheel sensor. Is it possible that a bad sensor can be giving the computer a false reading or not a reading at all which could cause it to go into like a safe mode state?

I’ll be able to check and adjust my neutral pressures tomorrow. I was just curious about the wheel speed sensor.

Thanks

 

[PADDO]

The AHC ECU just uses the front wheel speed signals, so your rr fault isn’t impacting damping.
Edit. Drive with Techstream hooked up and you should observe the two values labeled STEP in the AHC data list change with speed, comfort switch setting and road conditions. They should both be “8” with the vehicle not moving then start to change as you drive. Front STEP and rear STEP won’t necessarily be the same.

 

[Kalino_74]

I did what you suggested and took a test drive with the Techstream hooked up to observe the value's in both the front STEP and rear STEP. They did start with "8" then moved through the progressions as I drove, all seemed fine.

The pressure readings taken today with a full tank of gas.
Front 6.1
Rear 6.7

A few questions I was hoping you could help me with.

1) The time it take to go from "L" to "N" is right at 34 seconds. I'm counting from when I push the button to when I hear the pump shut off. Does that sound about right?

2) I bled the system again just for good measure. When I crack the screw just a little I don't seem to get any bubbles but if really open it up and let it flow I get the tinny bubbles like shaking up a coke. I'm thinking this is due to the pressure of the system being forced through a small opening. What are your thoughts? I actually bled it twice and it did the same from both the actuator and the rear globe actuator

3) The front end seems to be a little smoother and the rear feels great. I could be wrong but I feel like there is to much preload on the torsion bars. When going over a speed bump the it rebounds very hard and even makes a clunking sound of sorts. I've cranked torsion bars on non AHC trucks in the past and It has the same characteristics. Is it possible that torsion bars are getting weak? I only have 82K miles but the truck is a 2002.

I really appreciate your help with this. I think I've read every thread to do with AHC issues trying to get to the bottom of this.

 

[PADDO]

I did what you suggested and took a test drive with the Techstream hooked up to observe the value's in both the front STEP and rear STEP. They did start with "8" then moved through the progressions as I drove, all seemed fine.

The pressure readings taken today with a full tank of gas.
Front 6.1
Rear 6.7

A few questions I was hoping you could help me with.

1) The time it take to go from "L" to "N" is right at 34 seconds. I'm counting from when I push the button to when I hear the pump shut off. Does that sound about right?

2) I bled the system again just for good measure. When I crack the screw just a little I don't seem to get any bubbles but if really open it up and let it flow I get the tinny bubbles like shaking up a coke. I'm thinking this is due to the pressure of the system being forced through a small opening. What are your thoughts? I actually bled it twice and it did the same from both the actuator and the rear globe actuator

3) The front end seems to be a little smoother and the rear feels great. I could be wrong but I feel like there is to much preload on the torsion bars. When going over a speed bump the it rebounds very hard and even makes a clunking sound of sorts. I've cranked torsion bars on non AHC trucks in the past and It has the same characteristics. Is it possible that torsion bars are getting weak? I only have 82K miles but the truck is a 2002.

I really appreciate your help with this. I think I've read every thread to do with AHC issues trying to get to the bottom of this.

Good to know the step values are changing with driving conditions.

1. 34 sec from L to N is to long, should be 15sec or less for L to N and the same for N to H. Suggests you could have a problem with the height accumulator or restricted pump output flow. What's the techstream pressure of the height accumulator? it should be around 10.4MPa and it should discharge between 300-400ml with the fluid being bled off from a fully charged state. If both of these check out then you could have an internal obstructions (sludge, O ring material, metal particulate) blocking the two filter screens in the pump limiting its output flow rate. Also, I've seen oil sludge build up around the pump intake to the point that flow rates are restricted too. Both conditions are easily resolved with a disassembly and clean. Does the pump dc motor sound like its laboring or struggling? It needs to rotate at rated speed for the pump to output its designed flow too.
2. Sounds normal, called Henry's Law. There is always dissolved gases (even what appears gas free) in hydraulic fluids and when you suddenly reduce that pressure micro bubbles form.
3. At 6.1MPa your front pressure is to low, back off your TBs 3.5 turns both sides to get a pressure around 6.8-6.9MPa. At the moment you’re over sprung and under damped. You’ve got to get the sweet spot of hydraulic preload pressure on the damper accumulators for them to function as designed. It’s all about balancing hydraulic damping during compression and rebound (and the velocity that the shock actuator displaced fluid passes through the actual damper orifices) against mechanical spring forces.

HTH

 

[Kalino_74]

First thing I'll do is get the front pressure in the 6.8-6.9MPa range. I was worried that I might get the rear pressure too high if I lowered in the front.

I do believe the pump is laboring and is having a difficult time maintaining pressure. It sounds similar to one my children's battery powered trucks when the battery is getting low. The accumulator pressure when the pump is done pumping ends up a 10.4MPa so that's good.

I will do a bleed after getting my pressure in spec and will measure the amount of fluid that I get. I will also do a search on cleaning the two pump screens. When I did the first flush after buying the truck it looked like it was contaminated with maybe power steering fluid which is obviously very bad but it wasn't like black or really nasty like some other examples I've seen on mud.

If the pump screens are clean do you think its safe to suspect my pump might be an issue?

 

[PADDO]

These AHC pumps are very robust, simple gear pumps with just three moving parts. The two micro mesh screens that strain crud can and do block up very easily with particulate and sludge over time and if the pump can’t draw fluid then you’ll get slow height changing operation and eventually no operation. But get your neutral pressure sorted out first, don’t be worried about grossly affecting the rear as its not borne out by any fact.
Edit. If it was previously topped off with power steering fluid then that’s not the end of the world, much better then brake fluid for example. Power steering fluid, having much higher viscosity and differing properties to AHC fluid, will mess with the dampening profile but won’t kill the system as such. We have to remember that AHC fluid is not only a working hydraulic fluid it’s also a “shock oil” too.

 

[Kalino_74]

Paddo,

Is it necessary to remove the pump in order to check/clean the screens? I’m still trying to find a write up or diagram that shows the screens.

 

[craaaazzy]

making sure I read this correct: "For some reason now my passenger side TB bolt will not turn CW or C. My truck is spotless underneath but I did spray with WD 40 for good measure. The driver side turns both directions with ease. I've tried putting the truck in H mode and I even lifted the front tires off the ground without success."

you are turning the TB bolt while the wheels are up in the air, correct?

 

[PADDO]

The two screens are internal to the pump so the pump/reservoir assembly needs to be removed from the vehicle. It’s then a matter of taking off the circular external pump housing which gives access to the pump. It’s retained to the main body and held together, its a sandwich design, by four cap screws. Undo the screws, and disassemble the pump sandwich and the screens are revealed. They are pressed in and can be cleaned in situ with a blast off 100% hydrocarbon cleaner or you can back them out with a pick to clean. Reassemble, install the pump/reservoir fill with fluid and let it sit for a while to assist the fluid in working it’s way into the pump housing/intake and fire it up. If it times out because it’s airlocked and can’t prime then force run it manually.

 

[Kalino_74]

Thank you Paddo for the info on the pump/ reservoir that give me a greater understanding of the pump.

So this morning I got my front pressure set to 6.7 and the truck still is very stiff up front. When I push down on the front bumper at the corners there is no compressing the shocks.

I did the 16 step damper test again and when I can easily compress the shocks by pushing down the corner of each bumper. It also drives really smooth in the first say 8 steps.

Questions.

1) While the 16 step is being performed does it bypass the certain parts of the AHC computer? It seems like whatever sensor tells the computer how much damping to send to the front shocks is faulty, but no codes. Could the AHC cpu be bad?

2) If everything seems to be working fine during the 16 step test does this mean all the individual components are working fine?