PSI gages bouncing from 90 to 135psi

[Cwellc]

I have a 2010 PROSTAR w/ ISX Cummings engine. Recently had the air comp replace a year ago and recently, the main air line off the comp replaced. Now my primary and secondary air pressure gauges are bouncing around. this happens while driving not while idling, when driving the psi is normally at about 135 but it bounces from 90 to 135psi, this happens within a couple of seconds. I also replace the air dryer, the whole assembly, the governor doesn't purges until about 135psi.

any idea what can the problem be?

[SquareOne]

When you say it's 'bouncing', is it happening rapidly, or is it actually 'bleeding' from 135-90psi?

I see you mentioned a couple seconds, which could indicate a very large leak if so... I've had the park air brake valve (on the rear frame under the 5th wheel) leak really bad on my Cascadia a few years ago. Only leaked when the brakes released because of the pressure applied. Easy to miss if you're in the cab. Only indication would be the gauges dropping and air constantly building and popping off.

[Cwellc]

(01-24-2024 )SquareOne Wrote:  When you say it's 'bouncing', is it happening rapidly, or is it actually 'bleeding' from 135-90psi?

I see you mentioned a couple seconds, which could indicate a very large leak if so... I've had the park air brake valve (on the rear frame under the 5th wheel) leak really bad on my Cascadia a few years ago. Only leaked when the brakes released because of the pressure applied. Easy to miss if you're in the cab. Only indication would be the gauges dropping and air constantly building and popping off.

Yes it happens rapidly, the PSI stays at 135 most of the time, then it drops to 90psi and within a second goes back to 135psi. I read somewhere that this problem could be electrical but again, I don't even know where to start looking

[SquareOne]

Such a rapid drop and recovery can certainly be contributed to an electrical issue, that is, if your air tank gauges are electronically controlled. The ones in my Cascadia are analog with air lines ran directly to them so they read whatever pressure is in the tanks, whether or not the key is on or off.

I thought you mentioned in your earlier post the governor pops your air at 135psi. If the governor is causing the air to pop continuously, then you have an air leak somewhere. If the gauges are dropping but then quickly recovering with no air popping, then I'd venture to say you have a momentary false reading.

**If you do have electronic gauges, maybe start with the sending unit at the tanks to see if there are any issues with the harness or plugs.

[Rawze]

Prostars/Lonestars are notorious for ghost problems whenever the fuses in the fuse panel start getting tarnished/dirty. Might want to replace all the little red fuses in the panel and see if it clears up
ref, with pictures: http://rawze.com/forums/showthread.php?t...1#pid12861