Fixing the AHC from hell (1 Viewer)

[IndroCruise]

Some of you people are genius.

Just trying to help spread "The Word" on AHC and TEMS matters. Once a bit of time is taken to understand these systems, it really is not very difficult, lots easier than other systems on the vehicle like Brakes, ABS, VGRS, ATRAC, Fuel injection (and Ignition for 2UZ-FE), Engine management and repair, AirCon, Steering, Transmissions, Axles, etc, etc, etc -- all of which are many many bananas way above my personal paygrade -- so no genius here

 

[Moridinbg]

I was extremely reluctant to open it, but here is a photo of the brand new pump. It is as expected and opposite of the one I have works

Something immediately obvious is that the gears are much harder to turn by hand on the new pump vs the old. And this is mostly due to the pressure of the two halves, when tightened with the two hex bolts. When they are not tightened the gears are pretty easy to turn, but once tightened there is more resistance.
On my pump, as can be seen on the previous page, the gears have dug in the shell, so there is less pressure on them than with the new shell.

I was able to drive for exactly a month with the old pump and just over 6000km. Went all the way from Mendoza, Argentina via San Pedro de Atacama, Chile, to La Paz, Bolivia where I had ordered the new pump ahead of time from Amayama.com
I left the AHC system working, but did not touch the height selector and left it in H. Liberally used the comfort switch. Every once in a while the system would drop to L and flash OFF, usually only the front and I would have to run the pump motor with reverse polarity a few times so that the system will return to N. Otherwise it ran normally and occasionally adjusted height. Towards the end it started turning off more and more often and required more and more reverse runs. I assume that once it starts cavitating, then it quickly deteriorates.

I was not able to order AHC fluid - it's considered dangerous item and there is a single can of it available in all of Bolivia in Santa Cruz. Problem is Santa Cruz is currently very politically unstable and there are multiple civil roadblocks cutting all travel and trade with the department until the government releases the right wing leader they arrested on coup charges. Huh.

Can't wait to put the new pump in tomorrow!

 

[TreatSmash]

I was extremely reluctant to open it, but here is a photo of the brand new pump. It is as expected and opposite of the one I have works

View attachment 3212323

Something immediately obvious is that the gears are much harder to turn by hand on the new pump vs the old. And this is mostly due to the pressure of the two halves, when tightened with the two hex bolts. When they are not tightened the gears are pretty easy to turn, but once tightened there is more resistance.
On my pump, as can be seen on the previous page, the gears have dug in the shell, so there is less pressure on them than with the new shell.

I was able to drive for exactly a month with the old pump and just over 6000km. Went all the way from Mendoza, Argentina via San Pedro de Atacama, Chile, to La Paz, Bolivia where I had ordered the new pump ahead of time from Amayama.com
I left the AHC system working, but did not touch the height selector and left it in H. Liberally used the comfort switch. Every once in a while the system would drop to L and flash OFF, usually only the front and I would have to run the pump motor with reverse polarity a few times so that the system will return to N. Otherwise it ran normally and occasionally adjusted height. Towards the end it started turning off more and more often and required more and more reverse runs. I assume that once it starts cavitating, then it quickly deteriorates.

I was not able to order AHC fluid - it's considered dangerous item and there is a single can of it available in all of Bolivia in Santa Cruz. Problem is Santa Cruz is currently very politically unstable and there are multiple civil roadblocks cutting all travel and trade with the department until the government releases the right wing leader they arrested on coup charges. Huh.

Can't wait to put the new pump in tomorrow!

Keep us updated, man I am planning an extended SA trip n my 100 and AHC failure is one of my biggest concerns

 

[Mike NXP]

I was extremely reluctant to open it, but here is a photo of the brand new pump. It is as expected and opposite of the one I have works

View attachment 3212323

Something immediately obvious is that the gears are much harder to turn by hand on the new pump vs the old. And this is mostly due to the pressure of the two halves, when tightened with the two hex bolts. When they are not tightened the gears are pretty easy to turn, but once tightened there is more resistance.
On my pump, as can be seen on the previous page, the gears have dug in the shell, so there is less pressure on them than with the new shell.

I was able to drive for exactly a month with the old pump and just over 6000km. Went all the way from Mendoza, Argentina via San Pedro de Atacama, Chile, to La Paz, Bolivia where I had ordered the new pump ahead of time from Amayama.com
I left the AHC system working, but did not touch the height selector and left it in H. Liberally used the comfort switch. Every once in a while the system would drop to L and flash OFF, usually only the front and I would have to run the pump motor with reverse polarity a few times so that the system will return to N. Otherwise it ran normally and occasionally adjusted height. Towards the end it started turning off more and more often and required more and more reverse runs. I assume that once it starts cavitating, then it quickly deteriorates.

I was not able to order AHC fluid - it's considered dangerous item and there is a single can of it available in all of Bolivia in Santa Cruz. Problem is Santa Cruz is currently very politically unstable and there are multiple civil roadblocks cutting all travel and trade with the department until the government releases the right wing leader they arrested on coup charges. Huh.

Can't wait to put the new pump in tomorrow!

Such a wild journey , glad to hear you're still chugging along. Good luck

 

[Moridinbg]

Keep us updated, man I am planning an extended SA trip n my 100 and AHC failure is one of my biggest concerns

Honestly, there is little to go wrong. Make sure the sensors are in good order - two of mine had some wear and were occasionally giving bad readings, but I replaced them before leaving.
If your truck is high mileage you might preemptively replace the pump. Mine was a Frankenstein between my original 450 000km pump (280k miles) and a donor 300 000km pump. A mistake in hindsight when the new one is just 100 bucks.

 

[Moridinbg]

So AHC failed again with the brand new pump and oil 10 000km later . Same symptoms - squeeling, C1762, AHC OFF. Without warning or anything. Got out of the car for a moment next to the road, got back in and noticed Height Indicator at L and OFF flashing.
I ran the pump a few times backwards (+ to pump motor negative) and could rise the truck back to N. Had to run it a lot more times in reverse than the old pump even when it was on it's last legs.
Took it apart, still turns with more effort than the old pump, there are some wear marks similar to the old pump, but way less pronounced.
Put it back together exactly as it was, now it wouldn't pump oil I am debating putting it back together the wrong way like the old one and seeing what happens.
I am getting much better at taking this s*** apart. Takes me about 10 minutes to get the assembly out of the car and the pump out of the assembly and I am loosing single digit millilitres of oil.

The oil is pretty dark already, but I do not think it ever stays for long cherry red. There was some amount of super fine black residue around the pump. Could it be that a seal is failing somewhere and the residue wears out the gears?

We have been driving on some horrendous roads. Right before it happened had to drove for hour and a half each way in and out to a peninsula on one of the most horrible roads I have ever driven on on this continent or any other. Millions and billions of potholes and potholes inside potholes with washboards in between. I have been driving much faster than local traffic, just because a little bit of speed makes the washboard somewhat more bearable.
The pump motor was hot and oil was at 67C.
Not sure if it was a cause or just coincidence.

I am pretty bummed. Seems like there might be more general fault with the system if a brand new OEM pump with new oil failed after 10k kilometres. I bled the globes, but could not bleed the accumulator - the bleed nipple is broken. It was happily reaching neutral pressure though 10.3MPa before the pump died.

If I manage to get it working will probably get it to N and pull the AHC fuse and ride like that. It's not too bad.

At least we are at the north eastern coast of Brazil now. Lots of endless white beaches covered by palm trees. Much better place to deal with AHC woes than the high altitude deserts of Argentina & Bolivia

 

[jLB]

I thoroughly enjoyed your refurbishment thread, and honestly I’m not trying to be an a-hole, but in your opinion, after this trip, is the comfort of the AHC ride, worth the in-trip hassle, vs a conventional suspension?

 

[ClassyJalopy]

I thoroughly enjoyed your refurbishment thread, and honestly I’m not trying to be an a-hole, but in your opinion, after this trip, is the comfort of the AHC ride, worth the in-trip hassle, vs a conventional suspension?

He is willing to say what a lot of us are thinking. I am very pro AHC but I'd be leaning towards removing AHC if I ever plan to take my truck to remote places too!

 

[Moridinbg]

I am sure that this thread will be the prime example why you should rip the AHC from your truck for years to come. But I still believe that the superior ride and wide range of adjustability is worth it, especially for trips like this.
I am very top heavy with ~120kg (~250lb) between the tent, awning and roof rack. We have driven countless thousands of kilometers on super twisty roads in the high Andes. The Sport mode makes wonders with the handling and preventing leaning and diving. I am comfortably driving faster than most of the rest of the traffic.
We have driven just as many thousands of kilometers of the most horrible ripios, washboards and potholes in Patagonia and the high deserts of Argentina and Bolivia. The comfort mode helps just as much to make this bearable, as the aired down 33” tires. Also, unlike conventional shocks, the hydraulic system can be driven for hours at high speed over the washboard without overheating.
Until it fails and it strands you god knows where

I left with an already compromised system with the franken-pump and never bled accumulator. I hope I will get to the bottom of the issue for both my sake and everybody else's.

 

[Rhetoric]

He is willing to say what a lot of us are thinking. I am very pro AHC but I'd be leaning towards removing AHC if I ever plan to take my truck to remote places too!

I would say his journey only reinforces how robust the AHC system is and it takes really pushing it to get it to fail. Plus I know he is going to get to the bottom of it for even more data.

So when someone whines about their “bad AHC” in their Mall Cruiser they can be pointed here and reminded about the durability.

 

[Escape Artist]

Good times ... love seeing someone else do this trek. I did it on a motorcycle just as all the riots happened, and the military coup in Bolivia ... was really wishing I was in a cruiser at that time. Perspective I guess. Let us know how things progress with the AHC. I have contacts all over Brasil, Argentina, Chile, Colombia, and Mexico so if you need anything - just ask.

Curious if you are going to do the BR319??? Curious to see if it ever got "improved" ... Cheers

 

[Moridinbg]

I tried to force the height control to stay in OFF with the button, but it disables it when driving >80kph.
I extended wires 4 & 17 that send wheel speed info to the AHC ECU so that I can trick it and keep it OFF.

Interesting thing I noticed is that when in OFF the active dampening (TEMS in AHC/TEMS) continues to work. The dampening steps (monitored with Techstream while driving) keep changing values and the comfort switch changes the base dampening step (4/2, 4/4, 8/8, 12/12 front/rear from Comfort to Sport).
With wires 4 & 17 disconnected the ECU assumes that the car is stationary and dampening defaults to 8/8, although it somewhat reacts to suspension travel and changes a small amount.

Just as I did the wheel speed override, the hydraulic solenoids gave up front & rear gate & levelling. Half the time I get Techstream errors about Gate Solenoid Circuit, half the time I can hear weird noises coming from underneath, where the solenoids are. Maybe they have been acting up all along which is why my old pump died and then the brand new one died after 10k kilometers
Anyway, now the car is stuck in N, as the levelling solenoids won't open. I guess that is a good thing as the pump acts up. The bad thing is that this freaks the system out, OFF starts flashing and dampening defaults to 12/12 which is the sportiest mode. But with 4 & 17 disconnected it goes back to 8/8.

The important part is that I am stuck in N and not in L and so we continue to the Amazon along the north eastern and northern Brazilian coast.

@Escape Artist that is the plan. We are getting on a boat from Belem to Manaus and then driving the BR319 to Porto Velho. Our visas expire on April 24th so we will have to have reached Peru by then as visa extension is impossible for us.

 

[Moridinbg]

Small update - I have driven about 25k kilometers (15-16k miles) now, LOTS of offroad included, with the solenoids and pump not working, but the suspension stuck in N.
Techstream showed low B+ voltage (low single digits) and there was somebody else here on Mud that had a very similar issue with similar errors and effect - it was a wiring harness problem. I decided that as long as the car stays in N I am not touching anything to avoid getting stuck in L in Brazil, where there is 50% tax on car part imports and horrible delivery services.

It was pretty much normal for the first 10k km or so, through the rainy season in the Amazon jungle and through the Andes. After that either it needed to turn on the pump to restore pressure or a levelling solenoid that connects the left and right suspension circuits got stuck open and the car started rocking like a boat left to right on the highway above 60mph. We are travelling at ~50 anyway to save on fuel, so I still left it like this to avoid disrupting it and getting stuck in L.

Now I am back home so I can finally sort this thing out. I had lots of water going into the driver side kicker panel due to a s***ty windshield reinstallation that I did, so I am counting on a harness/connector corrosion.

Good thing to know - if your pump or solenoids fail, but you manage to get the suspension to N - unplug the solenoids immediately and you can drive like that for a very long time.

 

[suprarx7nut]

Very cool update thank you. The nice thing about hydraulic systems is that they can seal very, very well and stay sealed with very little pressure loss compared to say, air.

I've seen a couple instances with low B+ voltage for AHC and the issue was wiring. In one case they already had a bunch of other electrical gremlins in ABS and traction control so AHC was just yet another system affected. I believe they had both a collision and windshield water damage.

Let us know if you even find the problem wire(s)!

 

[suprarx7nut]

Re-reading this now. If there was a restriction in the reservoir, it seems that would cause the issues you saw. Any reason you think inlet restriction upstream of the pump might not be the cause of the pump cutoff issue?

 

[Moridinbg]

I flushed it and cleaned it back then, but didn’t help.
My issue is surprisingly similar to the other big ongoing thread - new pump, when I had it apart it was not pumping, weak stream, etc.

 

[Moridinbg]

One year later, I finally fixed it. Long story short, it was the return valve, as recently discovered by @suprasvobodea in his own struggle and @LX470YYC in his.

I must say that the return valve is a new angle that I haven't seen discussed much before and might be the culprit for a bunch of issues reported throughout the years.
I have ignored it all this time pretty much only because it is under the bracket that holds the reservoir in place and I had a very stuck bolt holding it. Always removed the reservoir together with the bracket, which also made removing the pump cover a minor inconvenience. I also figured my issue is with fluid coming out of the assembly, not going back in. WRONG! Bad return valve prevents the pump from properly pumping.
I had found a workaround where running the motor backwards (swap + and -) allowed the system to work for a short while (from minutes to hours), that got me going for waaay too long time. Probably moved blockage around in the return valve.

Before that I had to replace front passenger shock (hydraulic ram) - mine suddenly snapped couple of months ago, also a first, from what I have seen. The amber plastic bits came from inside, I guess some kind of a collar or a stopper. A completely destroyed bushing and lots of shims. Driving around with failing AHC, often on bump stops, especially in the front might have had done that. Hole in the upper part is where I had to stick in a large scredriver to prevent it from turning, to be able to unscrew the top nut.

I also had broken bleed nipple on the accumulator since I got the car. I have a spare accumulator and made several attempts to remove mine, but **** those 2 bolts on top of the frame rail. Then I tried to drill out the old nipple and remove it with an easy out drill bit - no dice, it was super stuck. Finally went in with a 6mm drill bit and then tapped it with 7mm (original nipples are 7x1mm thread) - there was no trace of the original nipple or any boundary between it and the accumulator body, it was 100% fused! Removing the front globe and unscrewing the lines is essential to have the space to work and drill in a straight line.

I was kind of nervous about drilling into the pressurized accumulator, but figured if you go small, it should be fine, so I drilled with a 2mm first. Eventually fluid started spraying out. I stuck a tube to it to collect it in a bottle and not make a complete mess of the entire front drive side.

Eventually tapped the new thread, screwed the bleeder from the spare accumulator and of course, it leaked like a sieve - the nipples rely on a very tight fit between the nipple bottom and the seat in the body and of course drilling and tapping destroyed that.

That's when I found out that there are bleed nipple repair kits. Essentially an oversized seat with a nipple. So I went ahead, drilled out the opening to 9mm (there is plenty of material there) and tapped 10mm thread. Screwed in a 10mm seat with another 7mm nipple. The accumulator material is super tough and working space is limited, coupled with laying on your back, so thread was sloppy, but with plenty of thread sealer/glue it is holding up nicely. For the first time since owning it, I could finally bleed the accumulator.

I also threw in some new globes from Impex, levelled side to side and for the first time in almost 2 years and half of South America later, I finally have 100% working AHC!

I will be honest, the last month or so I was more or less ready to pull the trigger on a nice set of adjustable shocks, like Icons or Kings and send the AHC back to hell, but after driving at 50mph through some speed bumps in Comfort yesterday with the body barely moving, potholes that I can't feel and then some tight country roads in Sport with the body staying level, even with the RTT counterweight on top, I am a believer again!

 

[LX470YYC]

This is fantastic news, Morid! Way to go with the accumulator bleeder as well. (and for taking photos while AHC fluid is spraying everywhere!) Mine's broken too - I'm just leaving it until it causes an issue, but it looks like over drilling, tapping etc will be the way to go when the time comes.

 

[suprarx7nut]

One year later, I finally fixed it. Long story short, it was the return valve, as recently discovered by @suprasvobodea in his own struggle and @LX470YYC in his.

I must say that the return valve is a new angle that I haven't seen discussed much before and might be the culprit for a bunch of issues reported throughout the years.
I have ignored it all this time pretty much only because it is under the bracket that holds the reservoir in place and I had a very stuck bolt holding it. Always removed the reservoir together with the bracket, which also made removing the pump cover a minor inconvenience. I also figured my issue is with fluid coming out of the assembly, not going back in. WRONG! Bad return valve prevents the pump from properly pumping.
I had found a workaround where running the motor backwards (swap + and -) allowed the system to work for a short while (from minutes to hours), that got me going for waaay too long time. Probably moved blockage around in the return valve.

Before that I had to replace front passenger shock (hydraulic ram) - mine suddenly snapped couple of months ago, also a first, from what I have seen. The amber plastic bits came from inside, I guess some kind of a collar or a stopper. A completely destroyed bushing and lots of shims. Driving around with failing AHC, often on bump stops, especially in the front might have had done that. Hole in the upper part is where I had to stick in a large scredriver to prevent it from turning, to be able to unscrew the top nut.

View attachment 3708097

I also had broken bleed nipple on the accumulator since I got the car. I have a spare accumulator and made several attempts to remove mine, but **** those 2 bolts on top of the frame rail. Then I tried to drill out the old nipple and remove it with an easy out drill bit - no dice, it was super stuck. Finally went in with a 6mm drill bit and then tapped it with 7mm (original nipples are 7x1mm thread) - there was no trace of the original nipple or any boundary between it and the accumulator body, it was 100% fused! Removing the front globe and unscrewing the lines is essential to have the space to work and drill in a straight line.

View attachment 3708109

I was kind of nervous about drilling into the pressurized accumulator, but figured if you go small, it should be fine, so I drilled with a 2mm first. Eventually fluid started spraying out. I stuck a tube to it to collect it in a bottle and not make a complete mess of the entire front drive side.

View attachment 3708101

Eventually tapped the new thread, screwed the bleeder from the spare accumulator and of course, it leaked like a sieve - the nipples rely on a very tight fit between the nipple bottom and the seat in the body and of course drilling and tapping destroyed that.

That's when I found out that there are bleed nipple repair kits. Essentially an oversized seat with a nipple. So I went ahead, drilled out the opening to 9mm (there is plenty of material there) and tapped 10mm thread. Screwed in a 10mm seat with another 7mm nipple. The accumulator material is super tough and working space is limited, coupled with laying on your back, so thread was sloppy, but with plenty of thread sealer/glue it is holding up nicely. For the first time since owning it, I could finally bleed the accumulator.

View attachment 3708111

I also threw in some new globes from Impex, levelled side to side and for the first time in almost 2 years and half of South America later, I finally have 100% working AHC!

View attachment 3708112

I will be honest, the last month or so I was more or less ready to pull the trigger on a nice set of adjustable shocks, like Icons or Kings and send the AHC back to hell, but after driving at 50mph through some speed bumps in Comfort yesterday with the body barely moving, potholes that I can't feel and then some tight country roads in Sport with the body staying level, even with the RTT counterweight on top, I am a believer again!

Wow! Amazing find. So with the return valve issue - what's the fix? Disassemble and clean, reassemble?

Congrats on seeing it through.

This is fantastic news, Morid! Way to go with the accumulator bleeder as well. (and for taking photos while AHC fluid is spraying everywhere!) Mine's broken too - I'm just leaving it until it causes an issue, but it looks like over drilling, tapping etc will be the way to go when the time comes.

Why not just buy a new accumulator?

 

[LX470YYC]

Why not just buy a new accumulator?

Money, time, not an issue yet, and I hear it's a huge PITA to remove the two bolts top side of frame... so I'll avoid as long as I can!

Gotta save room on the credit card for some DT headers...