07 volvo780 air pressure problems

From experience Volvo dealers are the worst at throwing parts at a problem and see what sticks, at your great expense. With what you've already done it only leaves the tanks, hoses, fittings and suspension bags. I'd be looking at hoses and fittings, get a spray bottle, 1/2 water and a squirt of soap and spray everything looking for bubbles. I've found leaks that I could not hear with this method and it's quick and easy to do. With the age of truck the rubber components are at end of life and fittings will be corroding.

*Has the compressor been replaced? Spray that too, they are known to crack around the fittings. When the compressor kicks in does it take about the same time as it always has to get up to 130psi or is it taking longer than before?

 

Well how long does it take to drop down to 90?

 

First on your governor pressure range should be about 20 psi ( not from 90 to 130). You can adjust governor cut out by adjusting bolt
on the governor (under the cap).
Similar problem on my truck. Disconnect airline from governor to air compressor. Connect 120 psi air line with pressure gauge from another source to compressor unloader port (where governor airline was connected) and look if pressure drops your compressor unloader valve is bad.

 

I had the same thing only with a Cummins, couldn't find anything. Turns out it was the unloader valves inside the compressor, was leaking internally and you couldn't hear it.

 

On some compressors you just need to replace unloader valve kit(which is problem bad O rings), so not necessarily to replace whole compressor/

 

Was cheaper to re and re.