At a Cross-Roads with AHC -- Advice Needed!

[Humpzilla]

Hey All,

Just returned from an epic 2 week trip through Death Valley, the Mojave Road, and the Eastern Sierra's. During the trip, I experienced a few AHC faults, and I'm hoping to get some thoughts on the cause of said faults, along with some advice on how to proceed...

First ... the AHC faults. Specifically, there were two that I experienced.

1) Truck would not go into Hi while fully loaded up for the trip
2) Occasionally, both on the highway and off-road, the 'Lo' light indicator would come on for AHC. When this happened, the light was solid (not blinking) but there was no noticeable difference in ride height or ride quality. The truck definitely wasn't ACTUALLY in low. Also worth noting is that whenever I turned it off and started it up again, it would start up in 'N' and stay there for quite some time.

Second ... a bit of supporting info to help with the diagnosis:

* AHC pressures with truck loaded up (maybe 200 lbs lighter than we were on our trip) are as follows:
- Front: 6.6
- Rear: 8.4
- I'm at about 8 or 8.5 grads between low and high

So, the rear pressures are definitely out of spec. Which isn't a surprise. My LX has 252,000 miles on it and I'm fairly sure the rear springs have never been replaced. Add to that the fact that I installed a 200lb drawer system in the rear prior to our trip, and I wouldn't be surprised if that pushed the AHC far enough out of spec that it wouldn't go into high.

Based on my understanding of AHC, it seems like my "next logical step" would be to install some King Springs to get the rear pressures back in spec.

Now, a few questions for the group:

1) Based on what I described above, how confident would you be that my problem with the truck not going into high and the 'Lo' light indicator coming on randomly is a result of needing new rear springs?

2) I mentioned in the title that I'm at a bit of a cross-roads with AHC because up until now I have kept the truck and build pretty light. However, adding 200lbs of drawers and eventually wanting to add a roof-rack and possibly a rooftop tent has me wondering if AHC will be able to handle that additional weight, or if I might be better off swapping it out for a "traditional" lift.

Up until now, I've been a HUGE fan of the flexibility and comfort of AHC, and if a set of King Springs is likely to sort out my AHC issues AND allow me to add (possibly) a few hundred more pounds down the road, that seems like a no-brainer to me....I just don't want to be stuck "chasing" AHC issues like a game of whack-a-mole when I add a bit more weight.

Any thoughts / insights would be greatly appreciated. Thanks all!!

 

[Kabanstva]

I experienced those exact same symptoms with mine at only around 116k miles. Another thing that happened is we lost a ton of AHC fluid Highway driving which made the truck ride like it had bricks for tires. No leaks anywhere, just had a ton of fluid disappear. I didn’t care for the system anyways so we just took everything out.

Some AHC lovers will tell you to get heavier rear springs and re index the torsion bars before a trip like that to account for the extra weight. I didn’t wanna mess with that plus the whole fluid disappearing scenario freaked me out and it wasn’t something I wanted to deal with again.

 

[Rhetoric]

Hi, AHC lover here.

Decide what path you want to take now re: keep it or rip it out. If trips like that are your jam, then King springs seem like a good investment and would knock that rear pressure down (unplugging the temp sensor at the AHC pump will also knock that pressure number down a touch).

If keeping it:

• Do a full AHC fluid exchange.
• Invest in 4 new globes (Impex has globes for ~$650 shipped these days) - 8 grads is on the weak side.
• Install King Springs
• Tweak TBs

If you keep the AHC system maintained and set up the pressures on the "low side" expecting to add weight for adventures, you shouldn't really have to mess with it often. Drive more; worry less.

If not keeping it: Forget I typed anything here and enjoy a static suspension you could get on any boring 4x4.

 

[AN470]

I was in the same situation. Flushed the AHC fluid, installed king springs. Problem solved. Since then I have loaded the rear to the brim along with 4 passengers. No issues at all, goes into high, functions fine, rides smooth. Unloaded the rear pressures are a little low, but I keep some tools and recovery gear at all times so it's fine. I have factory bumpers and an aluminum dissent rack. I'm considering adding front and rear bumpers and keeping AHC.

 

[Jerzywerzy5]

I think what you are describing happened to me. I thought the system overheated trying to constantly level itself off-road. Now I turn it off when off-road and haven’t had issues since.

 

[LndXrsr]

I would heavily bet that Kings would solve your issues. If you had a rear pressure of 8.4 and were 200lb LIGHTER than your actual trip weight, your trip pressures were likely 1MPa higher than that reading. This would likely allow for N in most condition but pushing the failsafe mode at times (which is when you showed "L" on the dash but were likely still in N). Very unlikely you could get it to going to H like this as well. I had this same scenario towing my buddy's 4runner on a trailer when it broke down wheeling prior to installing my King Springs.

I'm very biased pro-AHC, but if you decide to keep it, just get some Kings and you'll likely drop into the low end of pressure spec partially loaded, which is perfect.

 

[suprarx7nut]

Hey All,

Just returned from an epic 2 week trip through Death Valley, the Mojave Road, and the Eastern Sierra's. During the trip, I experienced a few AHC faults, and I'm hoping to get some thoughts on the cause of said faults, along with some advice on how to proceed...

First ... the AHC faults. Specifically, there were two that I experienced.

1) Truck would not go into Hi while fully loaded up for the trip
2) Occasionally, both on the highway and off-road, the 'Lo' light indicator would come on for AHC. When this happened, the light was solid (not blinking) but there was no noticeable difference in ride height or ride quality. The truck definitely wasn't ACTUALLY in low. Also worth noting is that whenever I turned it off and started it up again, it would start up in 'N' and stay there for quite some time.

Second ... a bit of supporting info to help with the diagnosis:

* AHC pressures with truck loaded up (maybe 200 lbs lighter than we were on our trip) are as follows:
- Front: 6.6
- Rear: 8.4
- I'm at about 8 or 8.5 grads between low and high

So, the rear pressures are definitely out of spec. Which isn't a surprise. My LX has 252,000 miles on it and I'm fairly sure the rear springs have never been replaced. Add to that the fact that I installed a 200lb drawer system in the rear prior to our trip, and I wouldn't be surprised if that pushed the AHC far enough out of spec that it wouldn't go into high.

Based on my understanding of AHC, it seems like my "next logical step" would be to install some King Springs to get the rear pressures back in spec.

Now, a few questions for the group:

1) Based on what I described above, how confident would you be that my problem with the truck not going into high and the 'Lo' light indicator coming on randomly is a result of needing new rear springs?

2) I mentioned in the title that I'm at a bit of a cross-roads with AHC because up until now I have kept the truck and build pretty light. However, adding 200lbs of drawers and eventually wanting to add a roof-rack and possibly a rooftop tent has me wondering if AHC will be able to handle that additional weight, or if I might be better off swapping it out for a "traditional" lift.

Up until now, I've been a HUGE fan of the flexibility and comfort of AHC, and if a set of King Springs is likely to sort out my AHC issues AND allow me to add (possibly) a few hundred more pounds down the road, that seems like a no-brainer to me....I just don't want to be stuck "chasing" AHC issues like a game of whack-a-mole when I add a bit more weight.

Any thoughts / insights would be greatly appreciated. Thanks all!!

1. About 95% sure the rear pressures caused your trouble. Add King springs for a robust solution, or add 30mm spacers on your existing springs as a cheap means to limp along a little more reliably.
2. AHC can handle as much weight as you want. You simply adjust the front and rear springs to compensate for whatever you add. I run a "fully built" LX with front and rear armor, skids and sliders, drawer system, swing outs, 2nd battery, hydraulic jack, compressor, winch, etc.... It's all good. I run King springs and 30mm spacers in the rear and oem AHC torsion bars up front. Super comfy and gets into H with no trouble at all.

Buy yourself a set of globes from Impex (exchange rates are awesome right now so a FULL SET is under $700 shipped), King springs, 4-5 liters of fluid and consider picking up a used front and/or rear sensor from a forum member as a back up. That's a pretty safe formula for AHC. The only reason for non-extreme use cases to remove AHC, IMO, is rust. If you don't have catastrophic rust eating your undercarriage alive, then maintaining and repair AHC is relatively easy. If you've connected to the ECU to get pressure readings, you've already done the hard part.

 

[kwon-offroad]

I run King springs and 30mm spacers in the rear and oem AHC

Did you run the spacer when you did the Kings or add them later as you gained weight? Curious because I'm contemplating Kings and spacer now to get it out of the way but don't have much weight now aside from floor sliders (not full drawers), fridge, compressor-in-a-case, etc. We pack up heavy on trips though. But I'm thinking that may be too low on the spec for it to affect every day driving. My LC is a travel rig only, sits idle during the week, etc. Although I accept that adding a space on Kings post is easier than on the much longer stock AHCs.

 

[GTV]

Did you run the spacer when you did the Kings or add them later as you gained weight? Curious because I'm contemplating Kings and spacer now to get it out of the way but don't have much weight now aside from floor sliders (not full drawers), fridge, compressor-in-a-case, etc. We pack up heavy on trips though. But I'm thinking that may be too low on the spec for it to affect every day driving. My LC is a travel rig only, sits idle during the week, etc. Although I accept that adding a space on Kings post is easier than on the much longer stock AHCs.

Accept the fact that as your weight increases you'll probably have to get back in there and change springs and/or add spacers to keep pressures in spec. It's an easy job though. Aim to get your pressures on the lower end of spec for daily driving so when you load up you won't be above spec.

 

[suprarx7nut]

Did you run the spacer when you did the Kings or add them later as you gained weight? Curious because I'm contemplating Kings and spacer now to get it out of the way but don't have much weight now aside from floor sliders (not full drawers), fridge, compressor-in-a-case, etc. We pack up heavy on trips though. But I'm thinking that may be too low on the spec for it to affect every day driving. My LC is a travel rig only, sits idle during the week, etc. Although I accept that adding a space on Kings post is easier than on the much longer stock AHCs.

I did Kings and then spacers. It all depends on what weight you add and where it is. Weight in a swing arm is the worst case scenario, affecting rear springs the most.

My experience matched the predicted pressure changes very well. King springs reduced pressure by about 3.0. Spacers reduced it by about 0.5. Measure where you are now in your worst case load out scenario (sans passengers, perhaps) and plan from there.

Accept the fact that as your weight increases you'll probably have to get back in there and change springs and/or add spacers to keep pressures in spec. It's an easy job though. Aim to get your pressures on the lower end of spec for daily driving so when you load up you won't be above spec.

Yup, agreed. Especially for an "adventure" vehicle. Aim for your normal load to be in the low end of the spec. If you load up everything to simulate a full load, then aim for the center.

AHC is quite dynamic so it's not imperative to get it exactly right. People get scared by all the over-pressure anecdotes, but most those anecdotes come from vehicles where the pressure has never been adjusted. If you aim for the center of spec, you have roughly 1000 lbs of additional reliable capacity - even more if you're running higher spring rate springs like King. It doesn't have to be exact, you just have to make some sort of good faith attempt.

 

[kwon-offroad]

King springs reduced pressure by about 3.0. Spacers reduced it by about 0.5.

Thanks @suprarx7nut - this is exactly the info I was looking for (sans not searching for it yet).

 

[LndXrsr]

Thread 'The ABCs of AHC - How to Measure, Flush, and Adjust all in one place'
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

Compiled this a while ago. @suprarx7nut has a nice cheat sheet in there as well. Post #6 will have the info you want about mods and reducing pressures.

 

[Humpzilla]

1. About 95% sure the rear pressures caused your trouble. Add King springs for a robust solution, or add 30mm spacers on your existing springs as a cheap means to limp along a little more reliably.
2. AHC can handle as much weight as you want. You simply adjust the front and rear springs to compensate for whatever you add. I run a "fully built" LX with front and rear armor, skids and sliders, drawer system, swing outs, 2nd battery, hydraulic jack, compressor, winch, etc.... It's all good. I run King springs and 30mm spacers in the rear and oem AHC torsion bars up front. Super comfy and gets into H with no trouble at all.

Buy yourself a set of globes from Impex (exchange rates are awesome right now so a FULL SET is under $700 shipped), King springs, 4-5 liters of fluid and consider picking up a used front and/or rear sensor from a forum member as a back up. That's a pretty safe formula for AHC. The only reason for non-extreme use cases to remove AHC, IMO, is rust. If you don't have catastrophic rust eating your undercarriage alive, then maintaining and repair AHC is relatively easy. If you've connected to the ECU to get pressure readings, you've already done the hard part.

Thank you! This is all great insight. BTW, the only reason I was able to connect to tech stream and get pressure readings was because of your super helpful video. So, huge thanks for that!

One (sort of) random question regarding install of the King Springs .... this is a pretty straight-forward install, isn't it? Personally, I don't really have the tools, the space, or the time to install them myself, so I'd be looking at having a shop install them. The shop I take my LX to gave me a quick quote over the phone of $625 + tax to install .... but I think they guy who quoted me may be mistaking the spring install for rear shock install. He said it would be less if it was more straight-forward, but on his end he saw that it might be necessary to bleed the AHC system as part of the install.

But....that doesn't sound correct to me. Just curious if you can confirm that bleeding the system is not a part of the rear spring install? Also, how long would you expect the install to take for a shop? I can't imagine it would be more than a few hours tops?

Anyway, thanks again for being a truly AWESOME resource for the MUD community!

 

[Humpzilla]

Thread 'The ABCs of AHC - How to Measure, Flush, and Adjust all in one place'
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

Compiled this a while ago. @suprarx7nut has a nice cheat sheet in there as well. Post #6 will have the info you want about mods and reducing pressures.

Thank you for the feedback! Your thread is an awesome one, and one that I've referenced more than once in the past. THANK YOU for taking the time to put it together (and for offering great insight in this thread)

 

[Humpzilla]

To everyone who offered insight in this thread .... thank you!

This is pretty much what I needed to hear. I REALLY like the idea of keeping AHC going....as long as it can handle the weight I'm going to ask of it and it isn't a nightmare to keep it going.

I'm going to go ahead and order those King Springs, get 'em installed and see how that does. I'll probably be looking at changing out the globes in the not to distant future...but I'll start with the springs.

Long live AHC!

 

[suprarx7nut]

Thank you! This is all great insight. BTW, the only reason I was able to connect to tech stream and get pressure readings was because of your super helpful video. So, huge thanks for that!

One (sort of) random question regarding install of the King Springs .... this is a pretty straight-forward install, isn't it? Personally, I don't really have the tools, the space, or the time to install them myself, so I'd be looking at having a shop install them. The shop I take my LX to gave me a quick quote over the phone of $625 + tax to install .... but I think they guy who quoted me may be mistaking the spring install for rear shock install. He said it would be less if it was more straight-forward, but on his end he saw that it might be necessary to bleed the AHC system as part of the install.

But....that doesn't sound correct to me. Just curious if you can confirm that bleeding the system is not a part of the rear spring install? Also, how long would you expect the install to take for a shop? I can't imagine it would be more than a few hours tops?

Anyway, thanks again for being a truly AWESOME resource for the MUD community!

Definitely not required to bleed AHC. The AHC system can be left intact. You just need to take care not to over-extend the rear sensor. I did not need to remove anything AHC related during my multiple spring swaps on my 06, but it's possible to lower the axle enough that it becomes a problem.

Turn off AHC, lift the vehicle, undo the lower shock bolts, carefully raise/lower each side until the spring can come out and if necessary remove the brackets for the brake line and rear AHC sensor. Again though, I did not touch my sensor either time I swapped coils.

Install should take an hour or two, I think. I'm notoriously slow, but I think I tackled the last one in under 2 hours. An unfamiliar shop being diligent might take 4 hours, but that seems a bit extreme to me.

Happy to help! It's enjoyable to see people benefit from it. My version of community service, I suppose.

**ALSO NOTE: Those lower rear shock bolts that need to be removed are *technically* one time use only. They are pre-treated with a threadlock compound from Toyota and they can and will walk themselves loose without it. Be sure to use new Toyota bolts or have the mechanic ensure red threadlock is used during reassembly. That's a simple little thing, but can cause a huge headache if it comes off during a road trip.

 

[Hercdriver87]

@Humpzilla I'm compiling components for my build 2006 Cruiser with AHC and you're scenario is exactly my concern. Thanks to everyone for sharing here, very helpful!