My CTIS is bricked(5 solid LED’s) so I am working on a electric over pneumatic manual control right now. It should be very do-able with a programmable microprocessor. The hardest part will be interfacing and interpreting the speed and pressure transducer signals. IMO, Nothing fancy in the control of the solenoids was employed. They are simply turned on or off. By using the valve design that they employed in the PCU it requires a combination of two valves to operate properly. This makes it far less likley that a single short circuit could over-inflate the tires(Extremely dangerous). My testing determined the following(all pressures taken from the transducer port on the PCU):
Control by itself: does nothing, it simply closes to seal the system for other operations or opens to vent the system.
Supply by itself: Pressure jumps to about 40, then decreases to around 5 PSI and front QR valve starts dumping tire pressure. without control closed, the air simply exits thru that valve which may setup a deflate scenario at the quitk release valves...
Deflate by itself: Nothing, solenoid activity only, no air is moved.
After playing around with it for a bit I came across the following:
To check pressure: Activate control and momentarilly activate supply to jump the pressure in the plumbing past the QR release point and open the wheel valves. Tire pressure will be read on the sensor port as long as the Control solenoid is maintained. Transducer port pressure was within 1-2 PSI of the tire pressure measured at the tires every time I checked it. This also equalizes the pressure in all 4 tires as they are all connected to each other. When the solenoid is released, the PCU vents axle/system pressure quickly, closing all the valves.
To inflate: Activate Control and Supply simultaneously. Pressure on the port jumps to around 85 PSI then down to about 5 PSI above the tire pressure as the wheel valves open and start taking air. Pressure on the port leads the tires by up to 5 PSI while filling. Filling of course is subject to the availability from the wet tank protection valve so it takes a while to inflate, especially at idle. To check pressure, release supply only and actual tire pressure is read on the port as long as the control solenoid is maintained. Re-activate supply to resume filling. Releasing both the solenoids purges the system pressure quickly and closes the wheel and QR valves without dumping.
To deflate: Activate Control and Deflate simultaneously. Pressure rises to around 8-10 PSI on the port, and both QR valves open deflating all tires equally...
I removed the pressure transducer(port is 1/8” NPT) and installed an adapter and hose from a 0-100 PSI automotive oil pressure gauge. I use 3 pushbuttons to control the solenoids, with the control pushbutton supplying power to the other two buttons so those solenoids cannot even be activated without activating control... The control button will also turn on the gauge light but I havnt wired that yet as I need to put together a 24V LED. I gutted my bad ECU and put the gauge and buttons there so I can use the power supplied to the ECU from the cannon plug. No real modifications so I can go back to an ECU by simply re-installing the pressure transducer, and a working ECU. I will write about it in the Manual CTIS thread with pics when I get it all put back together this weekend...
