Air dumping from rear under acceleration.

Topic: Air dumping from rear under acceleration. (Read 1852 times) previous topic - next topic

Air dumping from rear under acceleration.

August 14, 2018, 06:49:43 pm

Have read a bunch of HWH posts. Couldn't find this issue exactly. Please let me know if there is such a thread.

Work just completed: New air dryer complete, also repaired 14 air leaks which included six pack o-rings, regulators, drain valves. Inspected air system including bags, steps, fittings etc. Linkages to ride height valves okay. Replaced electronic air gauges with mechanical. I believe air pressures are good, front and rear, 100-130, steady. Only drop in pressure is nominal as expected with braking.

On final test drive this morning: coach loudly exhausts 6-10 seconds of air from rear leveling valves when under 100% acceleration from a standing start. Also can hear valves exhausting every 1-2 seconds while driving at speed, 40-60 and also when moving at parking lot speed. Tank pressures remained constant. While watching coach in a parking lot I observed rear moving up and down 1-2 inches in sync with the 1-2 second exhausting air cycle. Sound of air exhausting is same as when dumping. Inside coach it can be heard as coming from the ride height valves. The rubber boots on bottom of valves are missing and I guess must have been for some time. No debris, obstruction there etc.

All functions of leveling, travel mode, raise and dump perform normally. All engine temps etc. normal. Using Silverleaf to monitor them. Guys at shop not sure what gives, HWH CAN, control panel or ride height valves. (belief is something HWH electrical linked to accelerator ECM? and not ride height valves nor air compressor, governor)

What would cause a 6-10 second dumping from rear air bags when coach is accelerating hard, or 1-2 secs cycling air exhaust under mild acceleration?

Re: Air dumping from rear under acceleration.

Reply #1 – August 14, 2018, 07:26:03 pm

Mike,

When you say "rear leveling valves " and "ride height valves" are you using the same term for the ride height valves?
If so, have the ride height valves been changed out?
If they have been changed out they may have used 2 with no center "dead band" this would cause them to react too quickly.
After re reading they may have not got the ride height valves centered up properly when they were working on the linkage. (there is a center mark on them kind of like a mark in a timing gear)
Now this is just 1st guess need to think about this some more.

If it is the ride height valve exhausting this is really separate from the HWH. As all the HWH does in travel mode is open a valve to supply air to the ride height valves.

Pamela & Mike

Re: Air dumping from rear under acceleration.

Reply #2 – August 15, 2018, 12:05:52 am

Hi Mike,

Apologies for poorly written post. Ride height valves have not been changed out. I assume the rear leveling valves are actually the six pack of the HWH system.

4 sets of o-rings on six pack were replaced. Two of the 6 pack solenoids had no leaks.

Tomorrow we will wire separate indicator lights into each circuit at the 6 pack solenoids that energize the left/right dump function. Bring the leads up into bedroom and test drive to see if HWH is sending 12v to energize these solenoids. We don't know if problem is just one or both solenoids, or problem is further upstream to HWH rear CAN.

At some point we are also going to remove the brown connector in the HWH rear CAN to isolate the valves. At least this is what I've been told and my recall is fuzzy given this has been a very long day. Removing the connector is one of the tests i have read about on the forum and it was also suggested by James at FOT and a tech at HWH.

We're hoping it isn't the CAN. I've been told that HWH takes 3-4 weeks to rebuild one. We don't want that to be the only option. Starting two weeks ago, my wife took a medical leave of absence due to my health so we can spend time together traveling some. We are currently on the road. A 3-4 week delay blows a very big hole in our journey. If it is the CAN, is there any other quicker place to get a replacement??

Re: Air dumping from rear under acceleration.

Reply #3 – August 15, 2018, 01:27:14 am

Michael...fingers crossed on next round of trouble shooting.

Re: Air dumping from rear under acceleration.

Reply #4 – August 15, 2018, 06:53:31 am

Mike,

If the system was not exhausting before this work was done lets take a step back and look at what has changed.
You need to determine if the air is exhausting out of the ride height valves or out of the exhaust port on the rear 6 pack.
If it is the ride height valves working against each other the linkage has been misadjusted when they were checking them.
If it is coming from the 6 pack exhaust port then they need to find out which wire plug they transposed when they had the air solenoids apart to install the new "O" rings. All those wire connections can be swapped between each other and they will only work correctly in one order. The lights will tell you which valve has the wrong signal but the proper wiring diagram for your system along with the wire markers (hopefully they are still there on the wires) are your best bet for getting this fixed.
I would bet that they have 2 wire plugs (each plug has 2 wires) on the rear 6 pack solenoids transposed if it isn't the ride height valves.

What CAN are they talking about? If they are talking about the 6 pack manifold it don't just go bad overnight (unless they cross threaded one of the valves) as it is just an aluminum block that has been drilled, ported, milled.

Mike

Re: Air dumping from rear under acceleration.

Reply #5 – August 15, 2018, 10:06:05 am

Wire or airline swapped . Sounds like the HWH is fighting the ride height valves.

Re: Air dumping from rear under acceleration.

Reply #6 – August 15, 2018, 10:12:35 am

But, the HWH system should not be "active" when in travel mode.

Re: Air dumping from rear under acceleration.

Reply #7 – August 15, 2018, 01:41:20 pm

Quote from: Pamela & Mike – August 15, 2018, 06:53:31 am

What CAN are they talking about?

I think Mike (the other Mike) is calling the HWH brain box a CAN. As in CAN = Controlled Area Network. Perhaps he has a I.T. background.

Re: Air dumping from rear under acceleration.

Reply #8 – August 15, 2018, 02:23:15 pm

Quote from: wolfe10 – August 15, 2018, 10:12:35 am

But, the HWH system should not be "active" when in travel mode.

This is the reason he needs to find out exactly where the air is coming from then go from there. Something has been swapped either air or power while the system was down for repair.

Mike

Re: Air dumping from rear under acceleration.

Reply #9 – August 15, 2018, 04:20:19 pm

Checking now to see if connections at six pack were swapped. Anything possible but doubt it. 1.) Procedure at OMC is to do one valve at a time to avoid wrong connections. 2.)The leveling functions, front to rear, side to side, including raise and dump work properly when parked and when engine is running. Dumping of air from rear is only repeatable under hard acceleration, occasionally at lower speeds. Weird. We did unplug the CAN for the rear pack and the problem remained. Also problem remained when CAN was reconnected to pack. Meaning something mechanical happening?

On this coach the six pack exhausts through the ride height valves. There are no exhaust ports on the six pack. No work was done on the ride height valves.

Re: Air dumping from rear under acceleration.

Reply #10 – August 15, 2018, 04:26:48 pm

Quote from: wolfe10 – August 15, 2018, 10:12:35 am

But, the HWH system should not be "active" when in travel mode.

Hi Brett,
On our coach the raise and dump can be accessed when in travel mode as long as 5-10 mph speed is not exceeded. If speed is exceeded coach returns to travel mode. Wouldn't this indicate that the HWH is active in travel mode. But only for raise and dump.

As I write this I wonder if the transmission speed sensor is causing this rear dumping under acceleration? Grasping at straws here. Thanks!

Re: Air dumping from rear under acceleration.

Reply #11 – August 15, 2018, 05:17:59 pm

Quote from: Mike J – August 15, 2018, 04:20:19 pm

On this coach the six pack exhausts through the ride height valves. There are no exhaust ports on the six pack. No work was done on the ride height valves.

Mike,

This may be your problem. The exhaust port on the aluminum block could be stopped up with a durt daubber nest. I have never seen a coach that doesn't have a exhaust port on the aluminum block. It is hid behind the pressure switch. This would be the first coach that I have ever herd of to do this as you will need a special ride height valve and piping to achieve this action.

Quote from: Mike J – August 15, 2018, 04:26:48 pm

As I write this I wonder if the transmission speed sensor is causing this rear dumping under acceleration?

Isn't even connected to the HWH in any way.

Mike

Re: Air dumping from rear under acceleration.

Reply #12 – August 15, 2018, 05:59:32 pm

Quote from: Mike J – August 15, 2018, 04:20:19 pm

On this coach the six pack exhausts through the ride height valves. There are no exhaust ports on the six pack.

Mike J,

I agree with the other Mike (Pam&Mike) - I have never seen a 6-pack manifold that does not have exhaust ports. I can't imagine how the 6-pack exhaust function could be incorporated into the ride height valve. It would take a very complicated valve to do double duty. BUT, I'm not all that familiar with the 2000+ model year coaches, so I could be wrong.

Link below to the HWH Leveling System Textbook. If you have not seen this document, it may be helpful in solving your puzzle. Note that all the diagrams of the various rear 6-pack manifolds used in different HWH Series systems show exhaust ports (unless I overlooked one).

https://www.hwhcorp.com/ml20635.pdf

Re: Air dumping from rear under acceleration.

Reply #13 – August 15, 2018, 07:32:18 pm

I also agree with Pam and Mike. There's got to be exhaust ports on the 6 pack blocks.

Re: Air dumping from rear under acceleration.

Reply #14 – August 15, 2018, 10:52:09 pm

Perhaps a shot in the dark, but did they disconnect the linkage on the ride height valve? If so, and if they lined up the index marks on the valve body 180º off, the valve will exhaust air when they should be adding it and vice versa. This only affects the coach in travel mode. If only one of the valves had the linkage 180º off, the coach would drop on that side. I don't know if the effect would be as you described, but I thought I would mention it.
Don

Re: Air dumping from rear under acceleration.

Reply #15 – August 15, 2018, 11:32:52 pm

Yes on exhaust ports on six pack. My lack of HWH knowledge showed itself again! I got confused in conversation with tech here regarding where the system exhausts and/or dumps air from, six packs and ride height valves. Throughout this odd problem all HWH connected systems, level, travel mode, dump and raise have worked as they should. Also the new dryer purge valve would exhaust once front/rear tanks reached proper psi.

This is our diagnostic path to what I hope may be a solution: 1.) First replaced the ride height valves. The originals had lost their protective caps over the exhaust port. 2.) Tech support at HWH suggested that one or both of dump solenoids could be weak and allowing air to be released when the rear air bags become slightly compressed under acceleration. Everyone felt that to be a bit of a longshot but saw it as another way to narrow the possibilities. Especially since the packs had been serviced for leaks. Fortunately the air exhaust holes are threaded and so we plugged them for another test drive. 3.) With no air escaping and with the ride height valves replaced another source of air escaping became clear. The new Haldex air dryer, (installed 2 days ago) came with a faulty safety valve. The new mechanical air gauges on the dash indicated air being dumped then building quickly. 4.) Repair techs removed the plugs from the six pack exhaust ports, removed the dryer safety valve and plugged that hole. Another test drive and no air was exhausted during hard acceleration like before.

Tomorrow new safety valve gets installed in dryer then another test drive. At same time I want the ride height adjustments checked for Foretravel specification. We may have found the solution to our air exhaust/dump mystery during acceleration. If so, we made a classic mistake: We assumed that every new part we initially installed was also a good part.

Does anyone know the psi specification for the safety valve on a Haldex dryer? I'd like to be sure we get this right. And what are the correct ride heights for 2002 U270 travel mode, I assume this is measured at the air bags?

Re: Air dumping from rear under acceleration.

Reply #16 – August 15, 2018, 11:37:10 pm

Quote from: Don & Tys – August 15, 2018, 10:52:09 pm

Perhaps a shot in the dark, but did they disconnect the linkage on the ride height valve? If so, and if they lined up the index marks on the valve body 180º off, the valve will exhaust air when they should be adding it and vice versa. This only affects the coach in travel mode. If only one of the valves had the linkage 180º off, the coach would drop on that side. I don't know if the effect would be as you described, but I thought I would mention it.
Don

Thanks Don, the ride height valves are now replaced so I will check on this tomorrow. I think they are installed correctly but coach had some slight listing to one side when I saw them leave on final test drive of the day. Definitely want the ride height adjustment checked

Re: Air dumping from rear under acceleration.

Reply #17 – August 22, 2018, 11:16:15 pm

I'm happy to post that the air dumping has been solved. It was a headache for the service techs. They installed two newly rebuilt air dryer assemblies and both did the same dumping of air. Got my old OEM unit, serviced it and reinstalled. No more air exhausting during acceleration. Discovered that our original dryer had a 200 psi safety valve on dryer. The units delivered to us as replacements had a 175 psi. Another note: Trying to diagnose this they also replaced the rear ride height valves. One of those was defective.

The good news is my final bill for this work will be adjusted to reflect the bad parts and or decisions that were made. I can't say enough good things about Oregon Motorcoach Center. They have handled this well. Coach rides at right height and sits as it should. And we are now heading north on 97 towards Idaho.

My next forum search will be what members do to replace dryers for the discontinued Haldex model in our coach. I expect that someday the OEM dryer, purge valve and the internal air passages, ball checks, springs will need service.

Thanks to all of you who gave this some thought. The forum brain trust is a huge help as I learn what our coach is about.

Re: Air dumping from rear under acceleration.

Reply #18 – August 22, 2018, 11:33:41 pm

Quote from: Mike J – August 22, 2018, 11:16:15 pm

Discovered that our original dryer had a 200 psi safety valve on dryer. The units delivered to us as replacements had a 175 ps

I don't think you could ever see 175 psi anywhere in your air system, much less 200 psi. You should have a safety valve on your wet tank that will open at about 150 psi.

Re: Air dumping from rear under acceleration.

Reply #19 – August 23, 2018, 12:05:16 am

Quote from: Chuck & Jeannie – August 22, 2018, 11:33:41 pm

I don't think you could ever see 175 psi anywhere in your air system, much less 200 psi. You should have a safety valve on your wet tank that will open at about 150 psi.

Yes, our tank psi peaks at about 150. That psi shows in the rear tank gauge, (mechanical) and the front tank is less, about 135. The air safety valve on dryer is, I assume is on the inlet side coming from the compressor. Are you suggesting there may be a high psi issue between the compressor and air dryer? We do hear air dryer exhaust briefly every 5-10 minutes depending on roughness of road and how much we are applying the service brakes.

Re: Air dumping from rear under acceleration.

Reply #20 – August 23, 2018, 05:37:42 am

The D-2 valve regulates your air pressure,150 seems a little too hi,would check the gauge.There has been alot of discussion
about the hyd fans using horsepower,the air compreesor uses some horsepower too,the lower the pressure the less HP it will
use.

Re: Air dumping from rear under acceleration.

Reply #21 – August 23, 2018, 07:25:40 am

Mike J,

Just to clear up some confusion as to tank location and terminology so we are all talking about the same thing. As I read this thread it seems like we are talking about a couple of different things. If we can clear this up it will help me think things through and help other members out as to what they have.

You have 3 air tanks

1. The "wet tank" (term used before the time of air dryer but the name has just stuck) Chuck is talking about has no gauge unless someone has added one. This tank is located mostly above the rear end housing on most coaches of your vintage. It's pressure will be diffrent than what you see on the front/rear tank gauges due to various things like hose runs, check valves, & fittings.

2. The rear tank that has an OEM electronic gauge that you have changed to mechanical
3. The front tank that has an OEM electronic gauge that you have changed to mechanical
Both the latter 2 tanks are mounted right below the 2 front seats and this is where your gauges have there taps. These tanks are fed through one line from the wet tank should be piped parallel. Now with that being said they will always be slightly diffrent in pressure due to hose runs, check valves, & fittings between the 2 tanks.

As has been stated that pressure is somewhat high at 150.

Mike

Re: Air dumping from rear under acceleration.

Reply #22 – August 23, 2018, 08:34:55 am

Quote from: Mike J – August 23, 2018, 12:05:16 am

Yes, our tank psi peaks at about 150. That psi shows in the rear tank gauge, (mechanical) and the front tank is less, about 135. The air safety valve on dryer is, I assume is on the inlet side coming from the compressor. Are you suggesting there may be a high psi issue between the compressor and air dryer? We do hear air dryer exhaust briefly every 5-10 minutes depending on roughness of road and how much we are applying the service brakes.

We don't want to keep bringing things up that cause you concern about your coach - I know you guys are trying to get off on a relaxed, enjoyable outing. But when you mention things in a post that sound a little "off" to us, we feel obligated to speak up. In this case, the air pressure readings you report seem a little high.

I will expand on Mike's description (above). Picture a very simplified air system. There is a air compressor with a big hose leading to a air dryer. From the dryer another hose leads to the "wet" tank. From the "wet" tank a hose runs up to the front of the coach, where it splits and feeds into two more tanks, the "front" tank and the "rear" tank. Air can flow freely from the compressor, through the dryer and the "wet" tank, to the "front" and "rear" tanks. It should not, however, flow backwards due to check valves in the system. These check valves are located at the air compressor and at the inlets for all 3 tanks.

Air pressure in the system is regulated by the D2 governor. For detailed explanation, see link below. In simplified terms, during normal operation your air system should cycle between a low and a high pressure. Low pressure on our coaches is normally around 90-100 psi, and high pressure around 120-130 psi. When the high pressure is reached, the air dryer purges (blows off). At that moment, the pressure in all 3 air tanks should be almost identical. After that, tank pressures may diverge, depending on what components are operated off which tank.

Your air dryer purging every 5-10 minutes while driving sounds normal - no worries there.

What sounds ODD to us is when you say one tank (gauge) peaks at 150 psi and the other tank (gauge) peaks at 135 psi. They both should read the same pressure when the dryer purges. The other odd thing: 150 psi is a little higher than normal max pressure. This max system pressure can be adjusted at the D2 governor. The pressure differential between low and high pressure is a fixed range (usually about 20-30 psi), but you can adjust the high pressure point up and down at the D2. See the link below for the instructions.

Haldex D2 Governor Service Data

Re: Air dumping from rear under acceleration.

Reply #23 – August 23, 2018, 10:14:44 am

Mike J,with all the trouble you have had I would just get a new D-2 valve and install it,they are availible everywhere and is one of the
parts you should have a spare for.They are usually preset at 120 to 130 psi so you should never have any pressure more then that.

Re: Air dumping from rear under acceleration.

Reply #24 – August 24, 2018, 10:01:35 am

With different pressure shown on the gauges, check with a portable pressure gauge. That 150psi reading gauge may be bad.

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