I am still waiting on another Hitachi compressor. Reading the forums, these ebay compressors seem to have an issue with the pressure relief valve on the compressor. Whether or not it is the spring loaded pilot actuated valve or the control solenoid, I am not sure but it clearly will not release pressure. The original compressor did not have that fault. It simply burned up the motor because of the leaking front bags. That little check valve under the cap screw is purely mechanical and not an issue at this time.
I pulled the ride level control module, opened the can and checked for bad joints or burned components. It looks great.
Since I cannot find any external leaks with soap (front block, rear block, gallery block, gallery, compressor fittings, dryer, etc., I wonder if the pressure relief valve has something to do with it? I note that when I first installed the compressor, it raised to off road and then produced the fault. I could not lower the car. It sat for several days before the front dropped while the rear stayed up. Several more days and the rear also dropped.
Has anyone ever come across any location on the pressure lines that rubs or cracks other than at the locations I checked?

 

Like I said before, your code has nothing to do with vent issues or even compressor issues. Its a control issue. Good luck.

 

Latest -- I converted a couple of VOSS fittings to make them into sealing plugs. I then removed the front and rear air lines from the center valve block and installed the plugs. I manually filled the gallery and watched pressure. It was pretty stable. Maybe 8psi drop over 4 hours. Next I reconnected the front air line and repeated the test. Air loss went to about 1psi per minute. Did the same for the rear and got about 1psi per minute for the rear with the front blocked off. Connected both front and rear and still got about 1psi per minute loss. Soaped all valve blocks no visible leaks. I'm thinking about filling the system with Freon and using a digital sniffer to try to find the air loss.
BTW -- with fuse 3 and 26 removed, the car will sit fine for about 24 hours before it starts to drop slightly more in the front than the rear but both drop. All valves are new as are front struts. Compressor is new and works as advertised.
Are there any common locations on the lines that are prone to leak?

 

Starting to look the line itself from the reservoir valve block near the compressor and the front distribution valve block by the front wheel. I hope I am wrong, but you may want to soap more than just the fittings on all things connected to the front air system.

Keep us informed as you work through the problem. (otherwise, I would not look so smart talking very "technical" about Land Rovers at the office water cooler)

Jeff

 

Latest --- gallery line to the rear valve block near the VOSS fitting leaks. Replaced that piece of line but still have a very slight drop in gallery pressure (I NOTE that the gallery pressure is NOT the reservoir pressure (which is not measured on the car). Gallery pressure is just the lines between the compressor and the front and rear valve block UNLESS the center valve solenoid is open to allow air from the reservoir into the gallery. The gallery is also partially exhausted when the compressor starts to prevent the compressor from fighting high head pressures. This is the blow off you should hear as the compressor starts.
After replacing the front, center and rear valve blocks, as well as the compressor and front struts, the car now takes quite some time to rise and it does it a little on the rear then front over and over until it is up. The compressor runs the entire rise command time and the gallery pressure is about 150psi but shuts off at 232psi. I am thinking the reservoir is not opening to help when there is a rise demand. I am going to play with the center valve solenoid tomorrow. FYI, the center valve 12vdc solenoid wires go to the light grey largest connector C2321 on the suspension control module. Black/White is pin 8 (positive) and Black is pin 21 (negative) they should have about 2 ohms resistance if all is good. I may piggy back a small led on that line so that I can visually confirm when the solenoid opens the reservoir.

 

Keep going, the more I read the more I learn and this is all good information

 

The service manual had this description about the reservoir valve block:

The reservoir valve block controls the storage and distribution of air from the reservoir. The reservoir valve block also contains the system pressure sensor.
The reservoir valve block is attached to a bracket on the outside of the left hand chassis rail, between the reservoir and the air supply unit. The valve block is located within the air supply unit acoustic box to protect it from dirt ingress and damage from stones. The valve block has three attachment lugs which are fitted with isolation rubber mounts which locate in the chassis bracket which has three slotted holes. The isolation rubber mounts locate in the 'V' shaped slots and are pulled downwards into positive location in the slots.

The valve block has four air pipe connections which use 'Voss' type air fittings. The connections provide for air supply from the air supply unit, air supply to and from the reservoir and air supply to and from the front and rear valve blocks. The connections from the air supply unit and the front and rear control valves are all connected via a common gallery within
the valve and therefore are all subject to the same air pressures.

The valve block contains a solenoid operated valve which is controlled by the air suspension control module. The solenoid valve controls the pressure supply to and from the reservoir. The has a resistance value of 2 Ohms at a temperature of 20°C (68°F). When energised, the valve spool moves allowing air to pass to or from the reservoir.

The valve block also contains a pressure sensor which can be used to measure the system air pressure in the air springs and the reservoir. The pressure sensor is connected via a harness connector to the air suspension control module. The control module provides a 5V reference voltage to the pressure sensor and monitors the return signal voltage from the sensor.
Using this sensor, the control module controls the air supply unit operation and therefore limits the nominal system
operating pressure to 244 lbf/in2 (16.8 bar gage).

Since my rover "sneezes" at me every time I park it and adjusts the ride height, I get the feeling that the Galley is not pressurized except when adding air the the reservoir and struts or venting air from the struts.

Also:

Plausibility checks are checks on signal behaviour, as follows:

l Average height does not change correctly
° Height changes too slowly

l Gallery pressure
° Does not increase fast enough when reservoir filling requested
° Increases when system is inactive
° Too low when lifting is requested
° Increases too rapidly when filling reservoir
° Does not decrease when gallery is vented
° Pressure varies too much when inactive.

l Compressor temperature
° Sensor voltage too large - head and brush sensors (short circuit to battery)
° Takes too long to be readable after suitable compressor run time - head and brush sensors
° Does not increase when compressor active - head sensor only

l Sensor activity
° Signal floating
° Constant articulation when moving

So galley pressure leaking may not be a problem. But front end dropping is a problem.

Normal disclaimer: I might be wrong

Jeff

 

Today, I was planning on setting the ride height HOWEVER, the measured numbers were out of range and it would not let me do it. I am told that the NOMINAL service height is 473mm (+-2mm) Front and 483mm (+-2mm) Rear. All tires new and pressured to 40psig.

When I am in the program and the cross link valves open, I got 471mm LF, 468mm RF, 473mmLR, 480mmRR measuring from the center of the rim to the lip of the fender. If I put those numbers in the boxes, it says out of range and kicks me out of the program after 3 tries.
Reading the scan tool, I got +.236 LF, -.276" RF, -.118'LR, +315"RR with key on, engine off and door open, these numbers remained the same for 15 minutes so I do not think a bag is leaking. I think the system is all good except for not being able to set ride height.
I am sure there is some magic way to do the ride height but IDK.

 

Hm! seems like the ride height settings are incorrect so would suspect a couple of height sensors with bad connections or RS

 

All sensors new. Oscilloscope shows clean trace. No faults. I am thinking that the car sits crooked perhaps because control arm bushings are tight and during an alignment they tightened them when car was high or low causing a bind on the bushings. I might loosen up the bush bolts and see if the bushings release tension (obviously, I would use 4 corner jacks and get the car at the correct ride level measurement mechanically and make sure the body is also level. Perhaps that would then get me in range for the height calibration???
I sure love to hate these cars. Three in my stable.