Slow air pressure build

[VWtony]

Slow Air up..
Can I pick someone's brain on this thread? I have a '99 American Eagle that I purchased almost 2 years ago now and have had a problem with it building air pressure since day one..If I start it and just let it idle, it won't build up pressure unless I bring the rpm's up to 1500-1600 and even the it is very slow to build.
I hold these rpm's until it reaches around 65 psi and that noisy buzzer goes off! I can then idle it back down to normal idle speed and it will continue to build pressure to 130 psi..
Still at idle the pressure will SLOWLY decrease to around 110 at which it will increase normally back up to 130 psi..
My question is, where do I start to resolve this problem? I have replaced the drier dissicant and even had a mobile mechanic look at it and he replaced the governor(?)..it is mounted on the frame near the muffler and has a couple air lines mounted to it?? Do the dump valves have anything to do with the very slow air build and higher rpms's to get it to air up??


Thanks in advance for any info on this!

Newbie

[twinboat]

If you pressure drops to 110 after reaching 130 and purging and your not using the brakes or moving, you have a leak.

There is no other reason for the air guages to drop.

Find a better mechanic.

[VWtony]

Thanks for the response Twinboat..
I can understand I have a small leak when guages drift back down to 110 psi before compressor kicks in again and goes back up to 130 PSI, so I'll have to find that leak (can't hear it so it will be hard to find, I suppose).

Any idea what may be causing my main problem of having to increase engine speed so much to get it to even start airing up??

[twinboat]

Originally Posted by VWtony

Thanks for the response Twinboat..
I can understand I have a small leak when guages drift back down to 110 psi before compressor kicks in again and goes back up to 130 PSI, so I'll have to find that leak (can't hear it so it will be hard to find, I suppose).

Any idea what may be causing my main problem of having to increase engine speed so much to get it to even start airing up??

You may also have a leak in the lines from the compressor to the air dryer. They are hard to hear due to the engine noise.

They would only leak while it's running, due to check valves in the system after the dryer.

[RKins]

Make yourself some ramps like these and then get on a creeper with a spray bottle of soapy water and spray anything that has a hose going into it or looks like an air tank.


Look at moisture ejectors and see if they are leaking




Also check ride height valves

[KanzKran]

Originally Posted by VWtony

Any idea what may be causing my main problem of having to increase engine speed so much to get it to even start airing up??

Sounds like either a worn compressor, or bad check (reed) valve in the compressor's head or body that are sealing tighter at higher pressure.

[96 Wideglide]

Originally Posted by VWtony

Any idea what may be causing my main problem of having to increase engine speed so much to get it to even start airing up??

The faster the engine is turning, the faster the compressor is spinning.

It's taking that many rpm's to overcome the large leak you have somewhere in your air system.

[Tha_Rooster]

Originally Posted by 96 Wideglide

The faster the engine is turning, the faster the compressor is spinning.



It's taking that many rpm's to overcome the large leak you have somewhere in your air system.

Which in my opinion is a high idle rpm for a diesel.

[Gary RVRoamer]

Has the air dryer ever been serviced? Slow pressure build is a common sign of a clogged air dryer on the compressor.

[twinboat]

Originally Posted by Gary RVRoamer

Has the air dryer ever been serviced? Slow pressure build is a common sign of a clogged air dryer on the compressor.

He said in his opening post it was.

[Ray,IN]

Yes the air dump valve can be leaking, the only way to determine that is do what RKins recommended.

[Piros1]

As others have said you most likely have a leak, I would start as Rkins suggested. Get your rig up in the air, get a squirt bottle of soapy water, a creeper, and a pair of safety glasses and start spraying every line, fitting, and component related to the air system starting at the compressor all the way to the brake system. Since you don’t hear it when walking around it you probably have several leaks. I personally would go front to back and back to front to be sure I hit everything. Then document what is leaking with photos and start fixing. My second thought is you may have a weak/worn out compressor along with the air leaks adding to the slow air build. They do wear out and fail.

You did not mention what coach you have or I missed it, that would be could if you share this info in your post or add to your signature page.

[Ray,IN]

Originally Posted by Piros1

As others have said you most likely have a leak, I would start as Rkins suggested. Get your rig up in the air, get a squirt bottle of soapy water, a creeper, and a pair of safety glasses and start spraying every line, fitting, and component related to the air system starting at the compressor all the way to the brake system. Since you don’t hear it when walking around it you probably have several leaks. I personally would go front to back and back to front to be sure I hit everything. Then document what is leaking with photos and start fixing. My second thought is you may have a weak/worn out compressor along with the air leaks adding to the slow air build. They do wear out and fail.

You did not mention what coach you have or I missed it, that would be could if you share this info in your post or add to your signature page.

His profile says he has a 40' American Eagle. The air compressor should be good for 100,000 miles.

[Piros1]

Originally Posted by Ray,IN

His profile says he has a 40' American Eagle. The air compressor should be good for 100,000 miles.

I must be blind I didn’t see it thanks for letting me know. Typically I agree that the compressor should last 100,000 or more. We get 200,000-300,000 or more in my fleet of over 35 vehicles and 20 or so are air brake trucks on average but I have seen them fail in less than 50,000. I have also seen them prematurely get week and have difficulty supplying enough air especially with significant air leaks.