Signs the AHC is Going?

[Kigiin]

Ever since adding the 45 aux gas tank occasionally when stopping at the light, the truck will dip and then rise back up - very weird feeling. It kind of did this pre-tank install but it's more severe now. However just today I swear while driving 55mph plus I felt it do the same - kind scared the crap out me. It did it twice, I think, over a 30 minute period.

Other than not raising or lower (which it still does without problem) could these be signs of it going?

 

[geocruiser]

I know nothing about the AHC systems in the LXs, but maybe the system is telling you that you've reached the max weight that the AHC system wants to carry... at this point in it's life... and it is trying to tell you by doing what it's doing.

45 gallons of fuel = approx 390lbs.

The AHC system should be able to handle more than that, but it's 10 years old, and may need some maintenance.

The LX guys will probably chime in, and are more informed about the LX specific stuff than me.

Check the post by agaisin (Post #3) here: https://forum.ih8mud.com/100-series-cruisers/454969-why-loose-ahc.html

 

[Yukon LX]

maybe the fuel pump on the aux tank is interfering with the ahc. That thing has worker perfectly since day 1 right

 

[Kigiin]

Well it has been trouble free since I lowered it.

And this AHC doesn't always happen when both tanks are full.

 

[lexi4darin]

Is it happening when the tank is half full? Sloshing fuel around?

 

[Kigiin]

Actually come to think of it, it did occur with tank partially full.

 

[DallasCrzr]

Dd you check the ahc fluid level? Also was it changed every 60k miles because thats important. I know ahc has trouble with front and rear arb bumpers so 400 lbs of fuel is most likely causing strain because with anything else in the car youre not to far from maxing out ahcs lift rating.

You could always supplement with heavier springs or airbags. Both are relatively inexpensive especually when compared to an ahc system overhaul.

 

[agaisin]

See the section "Starting and Driving" about AHC in your owners manual (for '05 it's on p.273). You can search here for text in your owners manual: https://secure.drivers.lexus.com/lexusdrivers/info/my-lexus/resources/owners-manual-search.do

Here's the excerpt:

"The vehicle height cannot be raised if the vehicle load exceeds the following limits:
- up to 4 occupants [150lb per person] pluls about 660 lb in normal mode
- up to 4 occupants plus about 375 lb in the high mode

If the above load capacity is exceeded, the desired vehicle height may not be obtained even if the height select switch is pushed. (If the vehicle height cannot be raised in the normal mode and the height control indicator indicates "LO", this is because the vehicle is loaded too heavily. Under these conditions, drive your vehicle with due care.)

If the vehicle height cannot be raised even after unloading, push the height select switch on the "down arrow" side and then on the "up arrow" side. If this does not work, turn off the ignition once and then turn on. Operate the select switch again.
"

I don't know how much weight you've got in your vehilce, but do the math b/w gear, people and extra fuel. It's possible you're pushing the system right up to the brink of limp mode. Might be time to think about tweaking the AHC to accomodate the weight (been posted here before by others), or possibly swapping out suspension to something more appropriate for your use?

 

[lexi4darin]

Doing the math that sounds about right agaisin.

It was a while ago but I saw in my 2000 LX manual a 1,200 lbs limit. I don't recall it being broken down in the same manner for lo/norm/hi. I'll look for this later tonight or something.

 

[1loudLX]

Just loose you're ahc

 

[jOnathN]

Fuel sloshing would be too fast a change for the AHC to respond to. It is a height control not an active suspension.

I would bet that one or more height sensors are getting to be marginal. Suggest that you check all three for dirt and corrosion on the inside. A bad height sensor throwing stray signals could easily cause the AHC to cycle.

 

[RPMLX470]

Is it the front end or rear that drops and re-levels?

Before I replaced my front AHC actuators (aka globes), the front end would sometimes drop a bit and then it would re-level. Hasn't happened once since I replaced the front actuators (which were shot and the truck felt like it was riding with no shocks). My 99 LX is stock with bigger tires.

 

[Kigiin]

^ exactly what is happening. How much did the front globes?

 

[agaisin]

Is it the front end or rear that drops and re-levels?

Before I replaced my front AHC actuators (aka globes), the front end would sometimes drop a bit and then it would re-level. Hasn't happened once since I replaced the front actuators (which were shot and the truck felt like it was riding with no shocks). My 99 LX is stock with bigger tires.

Shout out to the AHC Gurus - could someone out there understand the connection b/w flat globes and frequent releveling as described above?

I'm not questioning the observation, just questioning the cause/effect correlation. I just don't understand how flat globes would lead to the frequent releveling symptom, but I would like to understand if there is a connection so please enlighten us!

 

[agaisin]

^ exactly what is happening. How much did the front globes?

Don't know where other poster got his or how much they paid, but...

1) B&B Aftermarket accumulators are 700 for the front pair, 800 for the rear pair, 1400 for all 4: Buy LX-470 or Land Cruiser 100 Suspension Accumulators

2) OEM Parts (from ToyotaPartsZone.com)
Front Accumulators 49141-60010 are 481 each (962/pr)
Rear Accumulators 49151-60010 are 497 each (994/pr)

 

[Kigiin]

^ for that price I would opt for a new suspension and lose the ahc.

 

[agaisin]

^ for that price I would opt for a new suspension and lose the ahc.

That's what many people do.

 

[1loudLX]

^ for that price I would opt for a new suspension and lose the ahc.

Bring it back out to Slees! Well, wait till ARB gets tbars back in stock.

 

[RPMLX470]

^ for that price I would opt for a new suspension and lose the ahc.

Yea, the globes are expensive.. I spent about 900 for the 2 fronts, plus a jug of AHC fluid at about 40 bucks. Labor was free, DIY. I (like many here) was tempted to remove the AHC system all out, but need to keep it for family convenience reasons.

Before the fix, the ride was bad. Front suspension felt like it had no shocks and riding on bump stops. I hated driving the car.. After I performed the replacement and got everything working normally, the ride felt smooth and I was pretty satisfied, didn't even think about the 900 spent anymore. It was worth it IMO (but everyone will have a different opinion on this based on their needs).

Keeping my fingers crossed on the rear actuators, they're still ok right now, but I'm sure they'll go out in the next few years.

 

[lpj23]

What spring and shocks combo would be the closest-to-stock ride if the suspension is changed from ahc to standard? The stock non-ahc suspension for the 100 is still a bit bumpy for me.