Air Brake Pressure Loss During Hi Boost On a Long Grade

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Air Brake Pressure Loss During Hi Boost On a Long Grade

March 26, 2024, 11:15:28 pm

I had air brake pressure loss on a long grade pull under full boost ( Boost @ 24 PSI ) I thought it was a stickily governor or air drier as when I stopped the pressure climbed normally. I also checked the air drier before it cycled and vented there was no air bleeding out the vent, While being a gauge hawk, I watched the air pressure and it did it again on a steep long grade under full boost, As soon as I back out of the boost, The air pressure climbs normally and kicks in and out like normal 110 to 130. Going down the highway it acts totally normal with no issue's at all. The air drier and governor where changed last January in 2023 and have at least 4K miles since the change out in 23 with no problems till now. Any Ideas or thought's? Thanks for the help. Mike

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #1 – March 26, 2024, 11:55:22 pm

Where does your air compressor air intake pull air from? Seems like the engine is sucking the air out of its supply.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #2 – March 27, 2024, 01:40:46 am

I just returned home so I need to start investigating and see if I can figure out what's going on, but that is what I was thinking also the engine is robbing the suction side of the air compressor, Hopefully it's something simple, bad or collapsed hose. I believe the air compressor is fed off of the engine inlet to the manifold.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #3 – March 27, 2024, 02:51:18 am

Quote from: craneman – March 26, 2024, 11:55:22 pm

Where does your air compressor air intake pull air from? Seems like the engine is sucking the air out of its supply.

On most turboed diesel engines, the intake for the air pump is from the intake manifold. So, more boost= MORE air for the compressor. Make a lot of sense-- requires only one air filter, air is "boosted" then cooled by the CAC before being fed to the air compressor.

Let us know where your air pump intake comes from.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #4 – March 27, 2024, 08:24:13 am

Might check the engine air filter for a restriction.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #5 – March 27, 2024, 11:08:27 am

I don't know what engine you have but I had an air issue on my ISM. Air was slow to build and would see a split in the air gauges occasionally. It turned out to be a leaking turbo controller. It takes air from the primary brake tank and controls the turbo output. I hope that's not your problem. It was a 2 coach buck fix.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #6 – March 27, 2024, 12:48:26 pm

I have the 8.8 ISL 400HP, Just started digging into this, Thanks for the info. I have read your complete post. My son who is a heavy duty diesel mechanic thinks it might be the reed valves in the compressor head getting weak and under full boost leaking. I will check into what you brought up and check to see if the ISL has some type of the same controller.

Also the air compressor suction does come off below the intake manifold what looks like it's part of the head, I just started to cut plastic tie wraps, to see what's on the head / intake manifold. I don't know what would be worse failed air compressor suction controller if has one, or the air compressor. both don't sound fun to replace.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #7 – May 13, 2024, 06:56:08 pm

Update to what I HAVE NOT FOUND with the Air Brake Pressure Loss During Hi Boost On a Long Grade.
After talking with several semi truck mechanics one being my son a 20 year experienced semi mechanic and 2, 45 year veteran semi mechanics all agreed that it should be the engine air compressor head "top end" reed valves or butterfly valve not holding or leaking during high RPM's, So I replaced the complete air compressor with a Cummins rebuilt compressor with all the hard piping and hoses. The water, air and oil. Including the discharge braided hose to the air dryer. Well that DID NOT FIX THE PROBLEM does the same thing not as bad, but it still is not wright. This does not make sense to me! I'm probably going to go ahead replace the air dryer and governor. Their both both only about 16 month's old. and do another leak check it holds air for days when shutdown and cycles about every 8 minutes while driving down the road. Any Idea's are welcome...

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #8 – May 13, 2024, 08:19:03 pm

Does your air dryer have an isolation valve? If so have you taken it apart and checked the O rings and seat? If it is locked up this could be the problem with the compressor cycling on every 8 minutes. If you don't have an isolation valve on the dryer was it left on the old dryer? Said another way did your old dryer have one?

Mike

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #9 – May 13, 2024, 10:04:36 pm

No Mike, no Isolation valve on the old air dryer. Or the new air dryer. Direct air line from the compressor to the air dryer Inlet. Have you ever heard of a turbo saver on a air dryer? I'm studying up on air dryer, I have a feeling it might be the turbo saver in the air dryer. Open for any and all Idea's. All new lines like I said in the previous post so no possible air leaks on the suction side of the compressor. The air for the compressor suction comes off the head below the main CAC air hard pipe going to the engine. There's no gizmo's in between the head and compressor regulating the suction air to the compressor. I also changed the air filter. It was do for a change anyways.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #10 – May 14, 2024, 12:56:41 am

Quote from: zmpm01 – May 13, 2024, 06:56:08 pm

cycles about every 8 minutes while driving down the road. Any Idea's are welcome...

This is a clue to me. My guess is that you have a leak due to something that is only using air when the ignition is on. I think the only thing that would do that would be the front step? Everything else should have air all the time, regardless of ignition. Or maybe something with one of the ABS valves? See if you can find a leak with the key on and the front door closed.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #11 – May 14, 2024, 08:52:01 am

Quote from: zmpm01 – May 13, 2024, 10:04:36 pm

No Mike, no Isolation valve on the old air dryer. Or the new air dryer. Direct air line from the compressor to the air dryer Inlet. Have you ever heard of a turbo saver on a air dryer? I'm studying up on air dryer, I have a feeling it might be the turbo saver in the air dryer.

What make/model air dryer(s) was(were) and is(are) now on the coach?

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #12 – May 14, 2024, 11:40:49 am

Michelle, The current Air Dryer is model # Haldex DA33100X, Current air compressor just installed is a Cummins # 5301094RX Supersession From the original model air compressor # 3949098, After thinking back the pressure loss didn't start until I changed the Air dryer in Jan of 23, We didn't take any trips with long grades until we went to Quartzite Feb of 24 where Hwy 20 Junctions with Hwy 10 in Texas. First time I noticed the pressure loss was on that grade climb. Now I'm wondering if I need the Econ valve / discharge check valve with the current setup Haldex DA33100X air dryer and the Cummins 530109RX air compressor,

Statement Reads: The Cummins/Holset E or QE Type Compressors require a compatible air dryer to prevent oil from passing into the air system. The dryer must maintain pressure in the discharge line while the compressor is unloaded, or an Econ Valve and Check Valve must be used in the system.

The problem I'm having is I'm losing pressure with the compressor loaded under full boost as soon as back off of the throttle It will build air pressure.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #13 – May 14, 2024, 11:43:37 am

My step was changes out to a dual electric step no air required.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #14 – May 14, 2024, 12:07:31 pm

How about the slide cover? It has been known to have a leaking cylinder in past posts. There was even a work around with an electric air solenoid. I bought one from a member who sold their coach as a spare if I ever need it.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #15 – May 14, 2024, 01:09:46 pm

Quote from: zmpm01 – May 14, 2024, 11:40:49 am

The problem I'm having is I'm losing pressure with the compressor loaded under full boost as soon as back off of the throttle It will build air pressure.

I went back and read your original post, but it does not give us all of the information we need.

Can you give us a step by step when you go in full boost what you are exactly seeing?
Are you seeing the front and rear air tanks pressures going down?
Both, either, all pressures holding at what it was before you went into high boost.?
How do you know the compressor is loaded?

Please break down exactly what you are seeing happen, step by step, when you are in high boost.
Does the problem start as soon as you go to high boost or is there a delay?

There are many parts to the complete air system with a number of check valves and protection valves. Based on what you are seeing will help us understand the problem.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #16 – May 14, 2024, 07:33:31 pm

#1. If the compressor is loaded and the psi is climbing. I can increase the throttle to hi boost above 20 - 24 psi, and the pressure will stop climbing, If I decrease the throttle to below 20 psi of boost, the psi will start climbing to the cut out psi, on mine 128# / cut in is 108 psi. That's why I say the compressor is loaded, I see it cut in at 108# and can manipulate it. Make the pressure stop climbing with the throttle.

#2. There is no delay, I can make it happen pretty fast.

#3. Front and Rear tanks will drop pressure equally if on a LONG GRADE PULL.

#4. SHORT PULL or making it do it purposely the pressure will hold in both the front and rear tanks until you let out of the throttle below 20 psi of boost, if it had dropped to cut in at 108# the pressure will climb. If it has not cut in it will just hold the pressure.

#5. Things acts normal going down the road cruising, cuts in at 108# cuts out at 128#

I hope that helps explain what I'm seeing let me know if I need to clear anything up. Thanks for everyone's help.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #17 – May 14, 2024, 07:41:55 pm

Craneman if by the cover you mean the step cover, our coach does not have a step cover. Only air by the front passenger wheel is the regulator for the foot well cover for the big boss! Passenger chair for the DW.! Or is that the cover your talking about? I'll check that possible leak source out. Thanks for the idea.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #18 – May 14, 2024, 08:13:44 pm

The cover that covers the steps in front of the passenger seat has a air cylinder to push it in and out. The dogs tell the DW when she forgets to slide the cover to the door.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #19 – May 14, 2024, 10:24:11 pm

Random thoughts

Just reread your post #7 and comment about high RPMs. Question is does engine need to be under load (high boost) or just high RPMs. I think I know the answer because you said it it normal going down the highway. So problem has to do with boost going over 20 psi?

Maybe instead of thinking the compressor is not producing air, how about during high boost there is a major air leak keeping the pressure from building. Maybe the air line to transmission retard leaks when transmission is under heavy load?

I know you already have spent a few coach bucks getting a new air compressor, but wonder about a rebuilt dryer and new d2

I can not think of anything on the air system that is tied to the of boost the engine is producing.

One test you could do, is pull the HWH travel fuse and manual level the coach. Then do the test. Going down the road the only thing that should be using air is the ride height controls and brakes. If you take the ride height out, then there is no reason for you to be loosing air pressure.

Are your check valves good? Way to test is run engine until cut out. Turn the engine off, then turn key back on but don't start. Open the drain valve for the wet tank, this valve should be in front of drivers rear tire. With the wet tank empty the front and rear tanks should be holding air. If one or both are going down fast, then the check valve by that tank is bad.

Out of ideas at the moment.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #20 – May 15, 2024, 10:51:48 am

Quote from: turbojack – May 14, 2024, 10:24:11 pm

Random thoughts

Just reread your post #7 and comment about high RPMs. Question is does engine need to be under load (high boost) or just high RPMs. I think I know the answer because you said it it normal going down the highway. So problem has to do with boost going over 20 psi?

Maybe instead of thinking the compressor is not producing air, how about during high boost there is a major air leak keeping the pressure from building. Maybe the air line to transmission retard leaks when transmission is under heavy load?

So we were both wondering along similar lines. Possibly the retarder accumulator solenoid valve?

Replacing transmission retarder valve (split from What did you do to your coach)

Air leak

Allison retarder air valve

Big Air Leak Hydraulic Accumulator

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #21 – May 15, 2024, 11:55:49 am

Quote from: Michelle – May 15, 2024, 10:51:48 am

So we were both wondering along similar lines. Possibly the retarder accumulator solenoid valve?

Replacing transmission retarder valve (split from What did you do to your coach)

Air leak

Allison retarder air valve

Big Air Leak Hydraulic Accumulator

One way to know for sure is cap the line of where it goes in accumulator.

I think we have given Mike a few things to try and will keep Mike busy for a while.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #22 – May 15, 2024, 03:10:46 pm

I would like to thank everyone for all the great idea's! This site and the all people on it are fantastic and really makes owning a Foretravel special.

After talking with Mike on the phone last night there is a good possibility it's the turbo saver and possibly a check valve leaking in the air dryer. Here's a statement below directly from the Haldex website.

The Haldex Turbo-Saver valve is an air dryer component that reduces horsepower loss for improved fuel mileage. It opens to allow compressed air from the compressor to "dump" directly to the atmosphere under high load applications, freeing up some horsepower. This reduces the load on the engine by allowing the air compressor to "free wheel".

Sounds like what I have going on, There's probably some other issue's like a possible leak in the system and bad check valve's.

All these headaches started after I changed the Air Dryer in January of 2023. The Quartzite trip in February of 2024 was the first trip with longer grade's.

Some things I verified. And answers to questions I had in previous posts.

My coach came with Part# N4250 Midland / Haldex air dryer verified by build# 6118 with Brad at FOT.
My Coach came with the Cummins Air Compressor Part# 3949098 verified by Cummins using the ESN on their web site. This combination does not require the ECON valve.

The direct replacements Haldex Air dryer Part# DA33100X replaced in Jan of 2023 and Cummins Air Compressor Part# 5301094 Just replaced May of 2024. This combination also does not require the ECON valve. The main component of requiring the ECON valve is the designation of a Q or QE in your serial number on your Holset Air Compressor. I'm sure there are possible exceptions to this.

Turbojack yes it is boost related not so much RPM related, I was trying to say RPM's were up do to being under full load on a grade and being geared down for the pull.

I will not have access to the coach until Friday, I'm going to get back on it A.S.A.P.

Again a BIG THANK YOU! to everyone for your help, time and idea's it is greatly appreciated. Mike

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #23 – May 15, 2024, 03:19:35 pm

At least it sounds you are headed in the right direction. It sure sounds like this "Turbo Saver" System is your problem. I had never heard of this before. Now the next person that has this problem will know were to go to solve problem.

And we now also have 3 mechanic know not to think of the reed valves on the head as the problem.

Re: Air Brake Pressure Loss During Hi Boost On a Long Grade

Reply #24 – May 15, 2024, 03:43:04 pm

That's a fact don't assume the worst and start with the easy stuff first! I should have put more thought into what have I just done or changed "duh I changed the AIR DRYER big dummy" it's still not over and I don't want to get over confident until it's confirmed.. I did learn a few new things why a ECON valve is needed, Compressor discharge hose length should be 12 feet to cool the air going to the dryer to help it be efficient. I wanted to cut it down real bad. thought that was stupid why's the hose so dam long.. My air compressor was the original The air dryer was changed at some point in time, all good information. I'm not trading the air compressor in for the core.

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