Lost air pressure. Springdale Montana.

I agree.

 

Well engine is a 1999 n14.
Air compressor was changed 2 years ago.
I had truck towed. I did all I could. I have the tools, not the parts.

Reading the replies posted. I think it is the unloader valve. Mechanic will only replace entire compressor assembly.

Now I rest in a hotel and wait for Monday.

 

Yes, I sprayed wd40 in both inlet and outlet.
After I called tow truck I got my hammer a smacked the darn compressor. That didn't help, but I felt better.haha.

 

Update. Compressor changed, new governor.
Initially when I hooked to trailer, pressure seemed ok.
I drove 60 miles the low and high pressures we're lower than before.
(I am always a little paranoid after a repair done by strangers). I called repair shop. They explained (I knew) why new pressures are different. " New governor settings".
BUT the kick in pressure kept changing. 105, 110, 90, 85. Not always the same.

The new time between cycles was about 3 times from before repair, 14 miles versus 4.5.

I wanted to get home so I set the cruise at 70 and off I went. Casually keeping an eye on air gauge. After another 30 miles things seemed to be ok.

Then both knobs on dash valve popped off. Pressure on both gauges 100psi. No warning light. or buzzer, I tried to push knobs back in as I pulled on road shoulder. Not enough air for brakes to release. It was after sunset now.
Quickly checked under truck and trailer for air leak. Couldn't hear any. I left truck running when I got out. I heard the dryer purge, got back in truck. Sure enough the pressure was up to 125. Checked maps, next exit 7.5 miles. Released brakes. Sure hope I can make it.

Next exit made it but darn the exit ramp is a "U" to the stop sign with the entrance ramp parallel to it, like a normal get on ramp. So as I come to stop sign, turn left, than backup to make left turn to entrance ramp. All the time hoping my brakes don't lock up again. After a few nervous moments as pressure drops to 90psi. I stop on shoulder.

Upon further inspection when I release tractor brakes all is ok. Then I push the trailer button on dash valve, the trailer brakes release but I hear an air leak. Air is venting out the exhaust thru the firewall. If I put my finger on the vent hose it pops both brake knobs.

So to get to a safe parking spot. I back off the trailer brakes. I have no load, empty stepdeck. Good thing this happened when it did. Just a couple miles further the interstate was ice covered and it was snowing slush.

After talking with my local mechanic he thinks the Tractor Protection Valve is bad.

Also sometimes the purge valve on dryer continues to flutter letting air out.

New compressor is working fine. Plenty of air volume.

 

To put the finish on this problem. When I got home I still had a leak out of the vent from the MV-3
I used a rebuild kit to fix the MV-3. I replaced the Tractor Protection Valve and the Quick Release Valve attached to the TPV. The MV-3 vent still leaked.

So I replaced the MV-3 valve. That solved the leak. The original body must have been damaged internally to allow the leak. The reason for trying the rebuild kit , I did not want to pull that octopus out of the dash!
While I was at it, I replaced the dash framework. Wow, that sure stopped a lot of the dash rattles.

I don't mind putting the new valves on the truck. As far as I know they are the originals. They aren't going to last forever. I also replaced the air dryer assembly.

I did replace my air compressor February of 2018. Seems a short life for the compressor.

Both primary and secondary air gauges are showing close to identical pressures when filling. I drove about 21 miles between hearing the air purge on dryer. Best of all, no audible leaks.

So back to work tomorrow. Well, back to driving anyway.

 

My valve was fluttering. That was another reason I changed the whole assembly. I held my hand under the valve and it was pushing some oil out with the air. Since I just had a new compressor installed. I figured the filter inside air dryer was in need of changing. For me it is easier to change the entire thing. I think the price difference was under $100.00 filter versus whole air dryer. Then I would have to buy and install the purge valve.

 

What I thought was the fix. Turned out not to be the fix.
After replacing the MV-3, the Tractor Protection Valve, the air dryer, governor and the Compressor.
I found the problem for the varying air pressure was caused by the Unloader Valve. (the black part mounted on the top and side of compressor)
It was old and worn limiting the volume of air not the pressure.
When the mechanic in Montana replaced the compressor, he cleaned the "check valve" and reinstalled it.
What he thought was the "check valve" was the Unloader Valve on the Cummins system.

I sure could have saved some money and frustration, if I knew what the function and what the Unloader Valve was. I would have changed it 2 years ago when replaced the original compressor.
Thanks to everyone that commented.