94 American Eagle - air system issues - stumped

[94Eagle]

1994 Fleetwood American Eagle, Spartan Chasis, 174K miles, 8.3 6CTA Cummins

I need more minds on this one to help troubleshoot an annoying problem I've had with the air system on my Eagle. I've kept some notes and provided a (brief as a could) summary below of the symptoms, what actions have been taken, and the results. It's more than annoying, it's a safety problem.

This system hasn't worked right in over a year and running out of big seemingly obvious components to replace. So, it's probably something obvious, just not to me and a friend who's a mobile mechanic, who can help to a point. He admittedly said from the start he's not a heavy truck air mechanic but knows the obvious stuff.

Please read, and let me know your thoughts. Thank you in advance.

April 2021:*

PSI Light came on while stopped at a tunnel inspection. I noted a lot*of air being released at the rear axle somewhere. Sounds like it's coming from near the differential.*
Fast idle barely made the PSI light go out. At each stop, the light flickered back on, barely made it home.*

On the next day,*cold start-up Front air system [Red needle] came up while the Rear system [White needle] stayed at zero until the front system reached 60 to 70 PSI.**[This is close to the same symptoms I have now May 2022, except now the rear system, comes up to 30 psi and stops until the front system hits 60 / 70 PSI]*

Also, the dryer purges every 10 to 15 seconds for a while until eventually just stays open venting air.*

May 9, 2021:

Replaced Service Valve. Improved results, no more PSI light at idle, and air leak at the axle gone, but pressures and purge valve still feel like a problem exists. At least we restored drivability. Air pressures are even, but still low.*

May 22, 2021:*

Replaced Purge Valve. Minor if any improvement, pressures will not exceed 90 PSI - the 10 to 15 purge cycle remains.*

July 16, 2021:*

Air pressures struggled to reach 70 PSI after 10 minutes of idle. The best we get at fast idle [2000 RPM] s 80 to 90 PSI. Air blowing past the purge valve.*

Governor replaced, no improvement.*

August 26, 2021:*

Replaced compressor [thinking it was a bad unloader]: Results, negligible change in symptoms. Note: Would just rebuild the unloader, but with the compressor having to be removed anyway, just wanted to eliminate all potential issues with the compressor/unloader [for less labor].**

August 29, 2021:*

Checked tank drains - do not recall what the pressures were, but little moisture,*noted oily mist.*

Sept 12, 2021:*

The dryer unit*was completely replaced. Broke a*fitting during removal fitting, fitting replaced.*

This was the greatest improvement overall, as now pressures hitting 120 then purging. Proved to be short-lived as in the next week [probably less time] I noted the rapid purge returned after the initial start purge hitting 120. The system bleeds down to 90 and hovers there. Sometimes it comes back up to 120, often it hangs around 90 to 105. The dryer*makes rapid purges, and the purge valve just stays open as it did the week prior with the old dryer.*

October 2021:*

Noted cold start-up, pressures are split as noted above in April 2021 "[This is close to the same symptoms I have now May 2022, except the rear system, comes up to 30 psi and stops until the front system hits 60 / 70 PSI]"*This is what we observe today May 2022***** except see next note below

April 2022:

Replaced air lines between gov/dryer. The main supply airline was not replaced. This seemed to correct the situation completely but was short-lived. The same symptoms returned the next day, on the next start up.*

May 2022:*

***After startup and initial purge, suspension fully inflated, I shut off the engine and kept pumping the brakes until gauges read close to zero, maybe 5 psi. Restart, both pressures came up evenly to*90 or so. This is different from the rear system stopping at 30 until the front hits 60 or 70 like it does*when the suspension is fully deflated.*

Drained top tank [not sure what system that is], oily water blew out.*
Rapid purge on the dryer remains.*

Appears we're chasing the same problem from April 2021 at the top of this summary.

With the oily water in the tank, I suspect the new desiccant*filter is trashed. And/or this is a result of the compressor having a near constant load on it as the system isn't operating properly and doesn't cut out often.*

Over the last year, I spent some time with a soap water spray bottle looking for leaks. Found some little ones here and there mostly at fittings at the foot brake [fixing those now, but seem to be too small to cause the problems], and another at a pressure regulator on an air tank. a*very small leak there will replace the regulator.*

I can post video recordings of these symptoms if needed once I figure out the proper format.

[mackwrench]

You inspect main air line from compressor to dryer?....as well as line from dryer to air tank.... sounds like you've had several issues that could have been related to the old dryer. The old dryer could have released stuff into tanks/valves etc... causing them to leak.

[NHRA225]

"On the next day,*cold start-up Front air system [Red needle] came up while the Rear system [White needle] stayed at zero until the front system reached 60 to 70 PSI.**[This is close to the same symptoms I have now May 2022, except now the rear system, comes up to 30 psi and stops until the front system hits 60 / 70 PSI]*

Red Needle is for Brakes and the White is For Air Suspension

[94Eagle]

Originally Posted by NHRA225

"On the next day,*cold start-up Front air system [Red needle] came up while the Rear system [White needle] stayed at zero until the front system reached 60 to 70 PSI.**[This is close to the same symptoms I have now May 2022, except now the rear system, comes up to 30 psi and stops until the front system hits 60 / 70 PSI]*

Red Needle is for Brakes and the White is For Air Suspension

Thank you. Maybe some systems are that way, and you made me double-check, which is always a good thing. But my systems appear to be front and rear per the manual.

However, your comment also made me think about when the air suspension actually starts to lift from a cold and completely deflated start. For my next start-up later today I'll take some notes.

[94Eagle]

Originally Posted by mackwrench

You inspect main air line from compressor to dryer?....as well as line from dryer to air tank.... sounds like you've had several issues that could have been related to the old dryer. The old dryer could have released stuff into tanks/valves etc... causing them to leak.

Other than the times the compressor and dryer were replaced, no. However, when I went through my notes and made the summary last week, the thought of disconnecting these lines, along with others to pressure check with gauges and an external compressor to try to further isolate the problem started to come to mind.

Maybe there's something internal like a check valve that is stuck open.

I can see having multiple symptoms and collateral problems, but they would usually be from a single point of failure. I'm mechanically knowledgeable from my former days as a jet aircraft mechanic and working on nearly everything I've owned since high school, but this is my first time tangling a heavy truck air system. So, I'm learning the hard way.

[NHRA225]

This might be a shot in the dark but I had an Air Up Issue about 10 yrs ago . My coach wouldn't Air up past 40 lbs and I needed to leave on a trip the next day. Called Spartan and the Tech I got was on the program and pointed me to my Norgren Air Valve which controls Air to the front and rear bags, Its also is the Dump Control for the Front and Rear- Mine was bad and I didn't have time to diagnose the valve so I ordered a new one --$750 plus NDA- Replaced the Valve and Systems been Good ever since. These Valve are rebuildable ! Just a Thought !

[bpu699]

Air system issues are frustrating.

You drove with the low air pressure light flickering on and off? Is that safe?

[mackwrench]

If you have access to a compressor, you can hook a air hose to the quick connect fitting, the same place a tow truck would use, and that will supply air pressure to the entire system, including the suspension. There's a one-way valve that keeps air from going back to dryer. But this will allow you to check for any system leaks.....

In your 1st post you say air dryer failed, chances are this is all progressive damage from it.

[94Eagle]

Originally Posted by mackwrench

If you have access to a compressor, you can hook a air hose to the quick connect fitting, the same place a tow truck would use, and that will supply air pressure to the entire system, including the suspension. There's a one-way valve that keeps air from going back to dryer. But this will allow you to check for any system leaks.....

In your 1st post you say air dryer failed, chances are this is all progressive damage from it.

All good stuff which I'll try over the next week and weekend.

As for the dryer failure, I really don't know if it failed, or was just part of the symptoms. Replacing the dryer, ruled out the check valve, purge valve, the filter, and dryer unit. The problem was thought to be resolved but very short-lived.

So, the governor was replaced, followed by the compressor as it was thought to be the unloader.

So what now I'm going to remove the main discharge from the compressor to the dryer and inspect the hose, likely replace it since it's the same labor to put it back. [and why not it's 28 years old and nearly everything else has been replaced at this point!], and replace the desiccant filter, blow out the lines between the tanks and try again.

Is there another check valve somewhere besides the one on the dryer?

[94Eagle]

Troubleshooting 101. Items in red are the two symptoms, first one if constant cycling of the purge valve, then later followed by a constant leak. Green indicates what's been done.

So I hope I'm narrowing this down now.

[94Eagle]

Originally Posted by mackwrench

You inspect main air line from compressor to dryer?....as well as line from dryer to air tank.... sounds like you've had several issues that could have been related to the old dryer. The old dryer could have released stuff into tanks/valves etc... causing them to leak.

That's what I'm starting to think yes.

[94Eagle]

Originally Posted by bpu699

Air system issues are frustrating.

You drove with the low air pressure light flickering on and off? Is that safe?

The light was only coming on at idle. The pressure stayed well above the minimum while driving but dropped quickly when stopped. Since I was only a few miles from home when this happened, I just wanted to get home in my driveway. So I kept it slow and the idle up. The brakes worked just fine, the issue I was more worried about was the brakes going in emergency while stopped, and not being able to move again.

[94Eagle]

Originally Posted by NHRA225

This might be a shot in the dark but I had an Air Up Issue about 10 yrs ago . My coach wouldn't Air up past 40 lbs and I needed to leave on a trip the next day. Called Spartan and the Tech I got was on the program and pointed me to my Norgren Air Valve which controls Air to the front and rear bags, Its also is the Dump Control for the Front and Rear- Mine was bad and I didn't have time to diagnose the valve so I ordered a new one --$750 plus NDA- Replaced the Valve and Systems been Good ever since. These Valve are rebuildable ! Just a Thought !

It's on my list to check. Thank you for sharing

[Ray,IN]

Hearing compressed air release near rear diff. Sounds like rear dump valve not closing fully.
After removing the old one I saw it might be cleaned and lubricated and replaced; but I already had a new one in-hand.