XM V6 99' bumpy ride

[Raatokalle]

Hi everyone.

Decided to ask for some advice before i start to rip and tear whole suspension system piece by piece trying to figure out fault.

Thing i have done/checked so far:
-Changed all spheres except anti sink one. Not really keen on dropping rear axle and breaking those long pressure pipes. They look already too crispy.
-Changed "HYDRAULIC CIRCUIT SAFETY VALVE" which is located around below drivers seat in "front left corner". This one i took from 2.5TD and i knew that car ran smooth. I didn't see any changes in how suspension worked after changing that one. So i assume car's own was fine also.
-checked some of the return pipes and tubes for possible air leaks. Didn't see anything suspicious tho.
-after closing driver's door and waiting ~30sec i can hear loud CLICK noise. If i remember correctly, it means active suspension does work?
-sport mode works like it should. After putting it on, in seconds i can feel suspension goes much more stiff all around.

And the problem is pretty much front suspension going completely hard for a brief moment when driving to speed bumps or driving on bumpy road at all. Can't really notice it when driving in slow speeds in city area, but outside and when driving fast, its very obvious. It's not continuous and happen randomly. Sometimes i can drive bumpy road and enjoy XM's god like suspension, other times front goes stiff for few seconds when ever it like.

Rear suspension doesn't do same as front, but instead it does have some other weird behaviour. One is when accelerating very hard, example for passing by, rear goes very low. After im done accelerating i can feel rear bouncing back to ride height. Other fault happens usually when driving in slow speeds in city. When stopping to traffic light, i feel some pressure "building on" brake pedal and when releasing pedal rear jumps all the way down. After few seconds, rear collects pressure and goes back to rideheight.

[white exec]

"And the problem is pretty much front suspension going completely hard for a brief moment when driving to speed bumps or driving on bumpy road at all. Can't really notice it when driving in slow speeds in city area, but outside and when driving fast, its very obvious. It's not continuous and happen randomly. Sometimes i can drive bumpy road and enjoy XM's god like suspension, other times front goes stiff for few seconds when ever it like."

This thread from 2016 should be an interesting read for you, as it covers many of the Hydractive issues (on XM and Xantia) you describe above...
viewtopic.php?f=3&t=55429&=xantia+revised+type#p494381

and a detailed write-up of how the revised-type valves were fitted to an XM...
viewtopic.php?f=3&t=55429&=xantia+revis ... 30#p505370

In brief, the original front and rear hydractive (stiffness regulator) valves relied on hydraulic system pressure being greater than centre sphere pressure to keep the valves in Soft mode. In practice, and with ageing of the system, sudden road bumps/ridges (and vehicle loading) could reverse the situation and cause the shuttle valves to momentarily jump into Firm position, causing the ride to become crashy just when it needed to be Soft. The revised-type valves are immune to this, and transform the ride of these cars.

[Raatokalle]

Thanks! Thats interesting to read. Well, next move is to scavenge those newer regulators OR find working ones from scrap XM. I assume there is no difference in suspension parts in different XM models as long as they are facelift XM like mine is.

[white exec]

After the early Hydractive ('H1') system, where there was only one electrovalve solenoid at the front of the car, hydraulically controlling both front and rear suspension regulators, the system changed to Hydractive 2 – at RP5929, 1 Feb 1993 – with identical regulators at front and rear, each incorporating their own electrovalve. This 'H2' arrangement continued until the very end of XM production.

So, any XM from RP5929 onwards would yield suitable replacement original regulators/EVs.

However, these units are generally reliable items (with the exception of the diode embedded in the solenoid coil) and before going to the trouble of replacing them, it would be worthwhile
(a) running the LHM system on Total Hydraurincage for 1500-5000km
(b) adding an external pair of additional protection diodes to the electrovalve supply lines
(c) adding a pair of monitoring LEDs, so operation of each of the electrovalves can be seen while driving.

Full details of all this can be found over on our sister site, club-xm.co.uk .

Finding a pair of the late-Xantia regulator valves might take a while, so a good idea to take the steps above in any case, as diagnosis and preparation for the new valves.

[xantia_v6]

With the original hydractive valves (not the later Xantia ones) the operation of the valves depends on the "line pressure" (the pressure from the main accumulator sphere) being higher than the peak suspension pressure. If for any reason the line pressure is lower than designed, then the hydractive valves will momentarily close when traversing a bump, or will fail to open reliably when commanded to by the ECU.

There are two common causes of low line pressure.
The first is a hydractive valve with an internal leakage, usually because the bias spring on the internal needle valve in the electrovalve has lost its set, this can be easily checked by examining the rate of flow in the hydractive valve LHM return line, it should be only an occasional drip. Any constant flow is a problem,
The second is that the main system pressure regulator has lost its calibration and is cutting the pump at too low a pressure. This commonly happens because the main spring in the regulator has lost some tension. The regulator pressure can be adjusted by adding shims under the spring, but a special pressure gauge and adapter is needed to measure the pressure.