Secondary air dropping

Can you remember what the final fix was if any? I have a 2007 International 9400i. I am trying to diagnose a problem with the 2nd tank loosing air pressure. It builds air fine and pops off around 120. It then looses about 30lbs and builds back up, constantly cycling. The air seem to be leaking from the dryer purge valve. Here is what is throwing me for a loop. If I shut the truck off just before it reaches full pressure and pops off the air does not escape and will hold pressure for a good amount of time, indicating no air leaks in my mind. If I shut the truck off after it pops off you can hear air escaping from the dryer purge valve. I changed the governor as it was a cheap place to start with no success. I am thinking it must be a check valve but am not sure where it will be located or looks like. I am hoping someone has seen this before and can advise me where to look instead of me just changing out parts blindly.

 

It is normal for air to purge out of the air dryer for 30 seconds or longer. If the air leaks down basically only when the engine is running, then I bet you have an ISX. Two things use air from the secondary system when the engine is running. Engine fan, and turbo actuator.

 

I think @Heavyd is on the right track. I would flip the fan override switch and see if that makes it stop. If it stops, you know it's somewhere from the solenoid to the fan. And if it didn't, break out the bubble water and start spraying. It could be the airline supplying that part of the system.

I've never had an issue with a turbo actuator, so can't give advice on how to diagnose it.

 

I've been having issues with the Air system on my 2006 9400i. ISX. Been a long battle with it and with winter here now it has got incredibly hard to keep up with. About 2 weeks ago I noticed air coming out if secondary tank right where the tank rests in the support rail. Is there a one way valve there? 2 days ago the front drives decided to lock up on me. I wasn't going fast and got off the road safely. After sitting there for 2 days, troubleshooting and trying everything I could to free up the drives, it decided to just work fine like nothing was ever wrong. I don't get it. At one point I thought dash valves were bad and at another point I thought air cans with park brakes in them were bad. Any thoughts on this? I'm thinking about replacing everything from the compressor back. Comppressor runs fine but I'm thinking air tanks, air dryer, governor, all air cans, 3 bendix valves, and lines.

 

Keep in mind I didn't replace anything when the drives locked up on me and it ended up working fine. Temperature outside was the same both the dats it was on side if road.

 

i am just going through the same issue... the tank fittings are leaking in my same truck. they cannot be repaired as too rusty. did you find replacement aftermarket tanks? OEM was 1500$ a side. any recommendations on where to buy the aftermarket ones?