After busting quite a few air struts .......Interested!

 

The beauty of this solution is that I still keep air suspension on the rear axle for load leveling. All I need to do now is develop a little mod chip using an Arduino to fake out the Wabco module. When the Wabco module commands the front suspension to lift, my chip will feed back a rising ride height signal. When the Wabco module commands the front to lower, my chip will feed back a lowering ride height signal. Simple. Even without that modification it works well. I drove it to lunch and back just now and didn't get a single fault code. There are also a million different ways to fake out the front suspension. You could just pull the front ride height sensors off, zip tie them behind the back seat and hot glue them in a neutral position if you wanted.

 

PWM leveling of the front headlights isn't a big deal. I'm sure mine aren't aimed correctly right now but I barely notice any problem. I've got a high resistance 2009 XFR strut sitting on my doorstep which should improve my ride even more. I'll install it tonight and post an update.

 

Just a quick update... I've had a long couple weeks at work and haven't had time to do anything with the suspension in a while. I've ordered the electronic components that I need to prototype a "fake-out" controller to keep my Wabco module out of fault mode. Mouser Electronics is shipping components via USPS and everything should arrive middle of next week. I've designed a two node low-pass filter to convert the 5V 490 Hz PWM signal from my Arduino ATMEGA chip into a steady DC signal with an 80ms response time which should be more than enough to simulate the motion of the front suspension in response to the Wabco commands for lift or lowering.

As a summary I can say that the ride under normal operating conditions with XFR ECATS struts and springs in the front and OE comfort air struts in the rear is superb! Without conducting any ride height calibration or any other modifications the car sits beautifully and rides smoothly and quietly with excellent handling response. Unfortunately after about 20 minutes of normal driving the Wabco module sets a fault for leveling plausibility and the suspension gets very firm.

I'll post a VERY SIMPLE circuit that should force all four ECATS struts into soft mode after I test it on my own car but it's really easy to switch the dampers from firm to soft electronically. Wabco drives the solenoids with a PWM signal because it is an efficient way to supply just the right amount of power to each coil. As with any solenoid you need a pull current and a hold current. If you want to pop the internal solenoid valve into soft mode without the Wabco controller you can supply ~1.25 amps for a fraction of a second and then hold the valve open with ~.5 amp. If you run the calcs you'll see that wiring two pairs of 5.4 ohm coils in parallel and wiring the parallel combos in series gives each coil about 1.1 amps while wiring all four in series gives each coil about .55 amps. So in theory you can build a very simple circuit with a diode and a toggle switch that just flips from off position to the parallel configuration and finally holds on the series configuration with a 12V DC supply. Assuming all four corners test at ~5.4 ohms and a fuse is installed to limit current below 1.5A that should be a safe way to force all four shocks into soft mode without any intervention from the controller. I was going to build that circuit before designing my low-pass filter for the Arduino but I'm so pleased with the ride quality as-is I didn't feel it was necessary to verify soft mode ride quality before jumping right into the Arduino design. When I cut into the wires for my Arduino circuit I'll rig up the simple DC test circuit described above and go for a drive and let everyone know whether it works as expected. I'll also have my high resistance 2009 strut installed by then so it will be a good test of full soft mode comfort over some local bumpy roads anyway.

Once I get my Arduino based "fake-out" controller built and tested my goal is to post a kit for sale that will give you everything you need to do a partial or full conversion to coil springs WITHOUT giving up factory ECATS performance! Part of the kit will be a drill template for drilling out the strut mount holes to match the XF / S-Type bolt pattern.

 

Sounds like a great idea ! Keep us posted.

 

pcmos, please do it! I will get up in the night and go back on STR setup when you show that simple electric scheme to feed struts by required current to stay soft. I recently lowered stock airs to STR setup height i noted when shifted back to airs.. as better it looks now as worse rides, too little pressures in bags causes to literally drift on boat and bump stopping on big waves and holes.. I need to give STR setup second chance! Spring setup ride feeling is second to none when compared to tired airs, but i never driven new airs to match it with springs.

 

Yeah if my controller works I'll design it so you can select to simulate front only, rear only or both front and rear with a 3 position switch. That will allow you to eliminate air on either front, rear or both axles without giving up ECATS. I'd like to source factory connectors as well so we don't have to cut any wires to install. I'm also going to try to operate the headlight level adjustment with my controller adding a manual adjustment for those who want to leave the headlights in one position. I'll make an effort to add front and rear ride height trim adjustments for those who want to use my controller to adjust the ride height using air.

I have some liability concerns about selling my drill pattern for the shock mounts but I'll post the design online for free.

 

Want to post an update... I tested my prototype control module last night with great success! My Arduino based controller / simulator is successfully responding to input signals from the four solenoid valve circuits involved in making the front suspension work and it is providing a proper output signal to simulate the change in ride height via two analog DC 0-5V signals. My low-pass filter is responding well and all I have to do now is hardwire it into the harness and go for a drive. The design took longer than expected because I needed to design an efficient switching power supply to get from battery voltage down to a nice steady 5V input for the MCU.

 

Andrew How is the progress with your controller? Can you suggest me the solution just for simple feed of current on shocks?

 

Bump for an update, I found your build interesting. Are you still planning on making a package kit?

 

Yes I am and I've made quite a bit of progress on the controller prototype but my plans came off the rails when the car quit running! I'm scrambling to figure out why it won't start and the suspension project has taken a back seat. I've also run into a couple of challenges with the controller design. I want to include OE style connectors so you don't have to cut the wires to install anything but OE connectors have a unique pin base pattern that won't solder to a protoboard. That means I would have to design a custom circuit board and have it produced for me or try to etch the boards at home.

Essentially I've written the code and I have my ATMEGA controller operational and properly simulating the sensor feedback response on LEDs. I've even designed a circuit that detects ignition shutdown and provides power to the chip for just enough time to save the ride height values.

What's amazing is that the XFR struts ride very nicely and the whole car runs great with the front air adjustment totally missing. The problem is that after about 10 minutes of driving the ASM module tries to adjust the front ride height and trips a code when it realizes the front axle isn't rising or falling on command. Once the code trips it defaults to "full firm" mode and the ride gets VERY stiff. My goal with the controller is to just fool the ASM into thinking that the axle with no air adjustment is rising or falling on command.

 

The 2011 XJ has rear air suspension with front springs. I wonder if you could do something with its controller to adjust rears while not expecting a height signal from the fronts.

 

Yes, that's exactly what my controller does. It basically sits between the front ride height sensors and the ASM and simulates the front ride height signal so that the ASM thinks it still has air up front. I know some folks want to delete air on just one axle and some want to delete air front and rear. I'm working very hard to develop the controller so that the user can select front air bypass, rear air bypass or both.

 

Right. I was just thinking you may not have to simulate a height signal from the fronts if you had a 2011 XJ computer that wasn't looking for a height signal from the fronts. Obviously that wouldn't cure the rears.

Based on SexyBeast's results, it seems the rear springs may not work anyway. He had to add some rubber to cure the slumping.

Last question, did you end up getting this to work with the 2010+ shock? There was no XFR in 2009, so a person would be limited to 2009 XF SC suspension.

If you could open it up to 2010+, we could use XFR shocks and of course get much newer shocks and have more options/availability.

 

Could a properly selected pressure transducer work? Higher pressure equals higher ride height (greater voltage), lower pressure means lower ride height (lower voltage). Of course it could react too quickly so a small air reservoir might be needed to slow the changes.

 

I thought the 2010+ CATS/ADS shocks required a different voltage & resistance than the previous generation CATS shocks. JLR changed the system at that point so the software compatibility was nonexistent for quite a few things that we could call "upgrades".

 

Just remember there are two main subsystems in play here. One is the eCATS shocks. Second is the ride height. You can use the Bilstein eCATS front shocks from the S Model to retain eCATS for shocks. This will allow you to retain the dynamics of dive and cornering soft/hard shock profiles. If you choose this, I would also suggest progressive rate springs. The second item is the ride height. As long as your settled height is calibrated to defaults by SDD after installation, the only time you may see the fault from adjustment is when the vehicle runs over 100mph when it attempts to drop the body by 15mm. Since this is not legal in the US, I'm not sure it is a valid concern. Just food for thought.