Activa Expert Advice Needed

[petef]

Hello all

My 96 Activa's front suspension becomes rock hard within 5 miles driving. At first I thought it might be dirty LHM blocking a valve or something but after cleaning reservoir and filters and replacing with Hydraflush the problem persists. Depressurising the system and then immediately repressurising leaves it the same. However depressurising and leaving it for an hour or so and then repressurising, the suspension reverts to normal for the next few miles until it becomes rock hard again.
The rear suspension is soft throughout and the electrovalves seem to be working normally - when the front suspension is soft and the engine switched off, electrovalves hum for about 30secs and then turn off with an audile click and the suspension then becomes hard - which I understand is what is supposed to happen.
Some spheres were replaced about 18 months ago including the front anti-roll ram balancing sphere. If this replacement sphere has become defective eg membrane gone, would this produce the solid suspension symptoms I am experiencing - or what might be other areas to look at?
The car is so hard at the front it bounces continually over bumps and is downright dangerous, so at the moment I can't use it.
Any advice would be most welcome.

[wurlycorner]

I'm not an expert on setting up active suspension (yet - I have that dubious pleasure still to come ) but I would suggest checking the ride height at the front. You might have what I suspect the problem is on my active, i.e. that the active roll ram is actually what is lifting the car, rather than the suspension spheres. That results in a completely solid ride.

[Stickyfinger]

Can the ACTIVA Ram lift it/harden the ride that much when the attachment is via the roll bar ?

[petef]

Just discovered that the car doesn't even have to be driven - just leave it stationary with the engine running and the front suspension goes solid in five minutes - something is pressurising it.

[Stickyfinger]

Can I ask what the "pump click rate" is

[Mandrake]

I think you may have two separate faults.

1) If it goes "rock hard" in the Hydractive hard mode, the front strut spheres may be flat. Have they been tested or replaced recently ? Hard mode should be firm and sporty at speed, but not rock hard. It will however feel nearly rock hard when you bounce the front by hand, but that is normal as you can't test the strut spheres with a manual bounce test due to the firm damper valves. They can only be evaluated by driving. (Or pressure testing)

To test whether the strut spheres are indeed flat, remove the fuse for the Hydractive computer (check the owners manual for the fuse number - it's one of the ones in the fuse box next to the battery) and then take the car for a test drive. The suspension will remain in hard mode all the time (centre spheres isolated) and feel like a heavily damped sports car, however it should NOT be bouncy, nor harsh. It will not be a soft ride but it should feel very safe and secure. You should be able to take judder bumps at a reasonable speed even in hard mode.

If you feel that the front is bouncing dangerously or the handling feels unsafe at the front then your front strut spheres are almost certainly flat.

2) If the car standing stationary goes from soft to hard at the front after idling for 5 minutes but the rear still seems as soft as normal then there is one of three things wrong, listed in order of likelyhood:

(a) The front Hydractive Electrovalve has a faulty back EMF diode or internal dry joint. This is a very common problem and can result in either permanent hard mode or intermittently dropping into hard mode when it should be soft, especially when the engine bay heats up. It seems to affect the front suspension far more often than the rear, probably due to heat buildup. There are three variations of this fault - open circuit diode, intermittent dry joint on the diode and intermittent dry joint on the coil.

The first two can be solved by soldering a suitable external reverse connected diode across the electrovalve, known on the forum as the "diode mod". Typically this is added to the wiring back at the ECU end of the cabling inside the black ECU box as its easier to get at the wiring there and it's a closed dry environment for the diodes. This problem is so common that most of us now do this modification to both electrovalves (three on an Activa) as a matter of course when we acquire a new Xantia... search the forum for pictures and description of how to do the modification.

The third variation of this fault is that the dry joint is on the connection to the coil itself - an external diode won't help here, only a replacement electrovalve or coil sleeve will help. (I had this problem on one of my Xantia's) A dry joint in the coil unit affecting the coil or diode is difficult to diagnose - it really needs an oscilloscope monitoring the switching waveform to see the subtle change that occurs when it goes faulty. So it's usually easier to just fit the diodes on all electrovalves and see if it fixes the problem.

(b) The front Hydractive Electrovalve has high internal return leakage due to a pitted needle valve - this can cause the suspension to intermittently stick in hard mode when it shouldn't. The only solution to this is to replace the electrovalve, which is fairly easy to do but they are hard to come by now... To test whether the electrovalve is leaking disconnect the rubber return hose on the top of the electrovalve and quickly plug the end of the hose so as not to siphon out your LHM tank, then connect a small clear hose from the top of the valve into a jar.

Start the engine and let the suspension operate - there will be a small brief squirt of oil when the suspension switches back and forth between hard and soft modes, however there should be no continuous flow when the car is sitting idling in soft mode. If you see a significant continuous flow the electrovalve needs replacing because the needle valve is pitted.

(c) There is low system pressure from the pressure regulator. This can be caused by a faulty pressure regulator or high return leakage somewhere in the system, or possibly a marginal hydraulic pump or air leak on the input of the pump.

You'd need a pressure gauge Tee'd into the pressure regulator output to test for low pressure, but its fairly unlikely to be this, and this fault would only affect cars made before March 1999 as the hydractive block design was modified to avoid this sensitivity to low pressure in later cars.

I think in your case you have an intermittent electrovalve putting the car into hard mode a lot more often than it should do, (possibly every time it heats up) which in turn is exposing flat front strut spheres.

Edit: as wurlycorner suggests, check the ride height is correct before the test I've suggested above.

[petef]

Thanks so much Mandrake and others for your responses, will investigate and report back in the week. I must get to the bottom of this.

[petef]

Ok, think it is sorted now.
Initially I tried out my pet theory and changed the front balancing sphere - no effect of course on the hardness of ride. But still a useful exercise because I had omitted the little rubber seal that goes into the sphere first time round. Wasn't leaking but who knows what might have happened.
Then I replaced the main front strut spheres - I had a pair of correct, old but low mileage Amtex spheres to hand. Immediate transformation - I now have front suspension which doesn't disappear after 5 minutes. What really threw me was the fact that the front suspension didn't become solid for 5 minutes, so I thought it couldn't be the main spheres . Didn't realise the recentlly replaced hydractive centre sphere could give a real spring to the front end by itself, even though the main spheres were shot. After this short while though the centre sphere was clearly being switched out..
So working my way through Mandrake's beautifully presented thesis on likely causes, I then examined the diode mod that I had carried out some 7 or 8 years ago - following the excellent article with photos by Richard Galagher in the Citroenian. Looked like one of the in 1n4007 diodes was not making good contact with one wire - my soldering skills leaving a lot to be desired. Anyway I have resoldered the diodes and neatly taped everything up again.
Now I have an Activa which is perfectly drivable and safe again. Thanks to all for advice, but particularly the mighty Mandrake.
By the by - whilst I could find many references to the 'diode mod', I could not find a blow by blow 'how to do it' article similar to Richard's original which I don't have with me here in France. Could someone point me in the right direction please, I seem to have only installed 2 of the 3 diodes irequired for the Activa - I obviously decided not to put the ram one in and would like to know where it goes for possible future action.

[CitroJim]

Hi Peter,

I seem to have missed this post until now...

The diode for the third (activa) electrovalve is easily installed in exactly the same manner as the other two. Identify the third (and only other) grey or white wire on the connector and solder in a diode exactly as for the other two... The third wire will be absolutely identical to the other two electrovale signal wires that already have diodes on them.

Mind the polarity of the diode - the banded end must go to the white or grey wire and the other end to earth (green/Yellow wire).

I cannot recall if yours is an S1 or an S2 but one has grey wires and the other has white..

[petef]

Thanks for this Jim, great to hear from you, tis actually a 1996 series 1. Guess I must have been so doubtful of my soldering skills at the time that I ducked out of the third diode installation. Found a bunch of the diodes I bought at the time still in the glovebox, so no excuse now that I have honed my technique on several vinyl tonearm rewires, and jukebox rebuilds over the years. Whilst the suspension is now perfectly ok, I still can't detect any difference when I put it in sport mode - seems pretty firm all the time, albeit hugely better than before I changed the spheres. Any way we will see what happens...........

[CitroJim]

Pete, if you can rewire a tonearm then the diode mod is absolute child's play!

Always fancied working on a jukebox... I'd love to know more about that....

[petef]

OK Jim, best not to venture too much off piste here. Suffice to say that there are many similarities between owning an old Citroen and a vintage jukebox - the main one being they can both lead you on a merry dance!
With a 50's, 60's, and 70's jukebox you are relying on electro-mechanical parts controlled by switching contacts, relays, motors etc. Not too different to a car and a lot of the same skills are needed to set them up and keep them going.
Equally I don't think I've ever met anyone who didn't like 45rpm vinyl jukeboxes from this era, especially the visible mechanism models where you can see the record selected, watch it play and then put away again. People of all ages seem fascinated - and you can choose the music to suit what you (or your better half) like. There is a total logic to the operation of a jukebox - the whole play mechanism being a series of discrete but linked processes usually detailed in the equivalent of Haynes Manuals which are readily available for just about every jukebox made.
They needn't cost a fortune - I've just bought a 75 Wurlitzer for £100, needs a bit of tlc but all there and now working. However if you want to spend £6000 on a restored Ami Continental you can do so.
What I'm really trying to say is that jukeboxes are enormous fun, but they can get under your skin - just like an Activa.
If you would like any more info just pm me.

[CitroJim]

Excellent Pete, thanks immensely for that I'd be in heaven with a juke box then

Especially if it has valves in it.... One of my other big interests is vintage wireless you see...

[petef]

Didn't know you were into old valve radios - I have a few of those too, Just about every jukebox made until about 1970 will have a valve amplifier. One or two carried on into the early 70's. Check out Ami, Rockola, Seeburg and Wurlitzer models from late 60's - non visible mechanism and so more affordable, but still valve amps. What should be attached if it has worked is pic of the amp in my 1953 Ami Model E.

[CitroJim]

Ohh, nice! I love it Pete

Yes, hugely into vintage wireless. In fact most of my regularly used wirelesses at home are valved and even my transistor ones are well over 40 years old...

I even have a vintage Leak stereo system in daily use too!