Air Supply for Tires and Tools
Tapping into the Range Rover Air Suspension for Compressed Air

Air supply 4.0


On lesser off-road vehicles it is necessary to obtain and install a separate air compressor and air tank in order to have air on tap for trail duties such as airing up tires after you have aired them down or repaired a flat -- or even to pump up a leaking tire temporarily to get you to the nearest service station.

Fortunately all late model Range Rovers come with a built-in air system, and it only remains or the owner to tap into it. Doing so also makes it easy to plug in a pressure gauge to help diagnose any faults in the electronic air suspension.

My First Installation
Installation of Air Line
The picture at the top of this page illustrates my initial air supply system on my 4.0SE. First, the drain plug on the air tank was removed (do it slowly to allow the air to escape before the threads are disengaged, and don't put your head in line with the plug in case it flies out). The drain plug was then drilled and tapped 1/8" NPT (outside the US you might wish to use whatever metric thread is convenient). This allowed a 1/8" nipple and elbow to be installed in the plug. I managed to get the elbow to point slightly upwards so anything attached to it would not hang down below the air tank.
(See photo at top right -- view looking forward)

The elbow was connected directly to a 1/8" to 1/4" adapter, since in the US most standard automotive and workshop air hoses and fittings use this size. To the adapter I screwed a 25 ft flexible coiled air hose and ran it over the top of the chassis rail, then forward using the space between the chassis and the bodywork (see photo). The coiled hose fitted neatly into this space and held itself there due to the lip on the inside of the  lower bodywork sill.

On the other end of the flexible air line, I attached a standard quick-connect fitting so that any kind of shop air tool could be attached in seconds when needed. In storage mode, the quick-connect fitting was wrapped in a plastic bag to keep dust out and poked into a hole in the side of the chassis rail. To use it, all I had to do was pull the quick-connect hose fitting out of the chassis rail and pull on the hose, which would neatly unravel and extend to its full length. Restoring it to its stowage position was equally easy.

An easier way to do this might be to use fittings that directly screw into the air tank.  Andy Cunningham reports the metric drain plug size to be 20x1.5mm on the P38/4.0/4.6. A blurb I came across from a company called RPM Off-road Motorsports indicates the plug on the outlet of the tank is 1/2 inch NPT. There is an unused plug on the center of the front of the 4.0 tank, and I am wondering if this is a 1/2 inch NPT as well. 

The System in Use
I found it very convenient being able quickly to attach a tire inflator, compressed air nozzle and other devices to the ready-to-hand source of compressed air. Friends are always amazed when you nonchalantly reach under the door sill, pull out an air hose and give their tire a shot of air.  Another advantage of the system was being able easily to attach a pressure gauge, for diagnosis of the EAS system. Even the dealer took advantage of this upon occasion. I did note try running air tools off the system, but there is no reason why this would not be possible in short bursts. (For serious air tool use, a more powerful source of air such as an engine driven compressor would be best).

The one shortcoming I encountered was that in muddy conditions the mud kicked up behind the front wheel tended to attach itself to the neatly coiled and stowed air hose, adding enough weight to it to make it droop down below the body sill. On one very muddy winter trip the hose fell right down and was run over by the rear tire, breaking the hose and causing all the air to escape from the tank.  I decided to devise an improved system for the future -- also preferably one that did  not require bending down to access the hose!

Other Approaches -- Work in Progress
I have often considered an alternative approach, namely to tap into the air system at the valve block and install a quick-connect fitting on the adjacent left front fender. I did not get around to this on my 4.0, but other owners have now done their own air systems. See the following:

Jim Haver installed an excellent tap into the air system under the hood with a built in air pressure gauge; see this link.

Be sure whatever air fittings you use can withstand 150 psi (10 bar) as some standard shop air fittings cannot.

Also, be aware of the possible confusing effects these air supply mods might have on the air suspension ECU. James Howard has been contemplating a similar approach for his 93 Range Rover, but he has been afraid to because he read in the shop manual that if the compressor runs for too long a time, the computer thinks there is a leak in the system and goes into fault mode. I have never run into this problem but it is worth bearing in mind if you are doing an extended airing up job!




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Page revised February 10, 2012