Rust repairs, Xantia rear. ECU protection?

[sparksie]

Hi all.

As detailed in the thread about back bumper mounts (there aren't any!!!), once I finally got the bumper off I found a nightmare of design incompetence.
There are triangular "buttresses" intended to provide rigidity where the rear chassis legs meet the back panel.
Due to inadequate drainage, these buttresses fill up with crud and rot away.
The off side one is gone, with a lattice of paint and brown flakes showing where it used to be.
The near side is still there, though crumbly and not providing any strength whatsoever.
My plan is to cut away all the teabag and weld in new metal. Given the hidden location, I don't intend to make it look remotely original and I certainly won't be leaving the water trap in place. In my design entrances will be smaller than exits, for waterborne crud!
My question relates to the need to protect the electronics from voltage spikes caused by the welder.
In olden times it was sufficient to disconnect the battery and unplug the alternator.
Nowadays, however, there's much more at stake. There are "surge suppressors" you can fit to the battery, but I can't bring myself to trust these for welding. They're designed to protect against the surges associated with jump starting, which are entirely different in frequency and magnitude, from those caused by welding.
I believe best practice is to unplug and remove the ecu(s) before starting.
However, a brief glance under the bonnet of the Xantia didn't reveal the necessary connectors.
Where should I be looking, on a 2000 reg Xantia 1.9 TurboD?
In addition to the engine/immobiliser ecu (which scarcely deserves the name, given mechanical injector pump etc), what else needs protecting?
Airbag controller? Pyrotechnic seat belt tensioners? I don't want the srs or airbag lights failing the next test, any more than the immobilser refusing to energise the stop solenoid!!!
Given recent events in the workshop (leaky petrol tank on an '88 BMW), I think I'll be doing this in the open, so fingers crossed for settled weather. It will be some time before I'll be confident dropping molten metal in the pit, but I can't stick it back together with the corners in this state, so out in the yard it's going to be! In Winter! Ho-hum...

[Mandrake]

The engine ECU (and Hydractive suspension ECU if the car is an Exclusive) will be in the black plastic box behind the right hand headlight - just turn the release screw and pop the top.

The CPH (immobiliser/central locking/alarm ECU) is up inside the dashboard on the passenger side - you need to remove the glovebox to access it - its in the top right corner after the glovebox is removed and has two connectors.

If the car is an automatic the gearbox ECU will be under the battery tray. (Remove the battery then unbolt and remove the tray)

Airbag ECU's I believe are on the individual airbags themselves, the passenger side being accessed through the removed glovebox, the drivers one is obviously in the steering wheel hub, I'm not sure the best way to access that to unplug it. Depending on spec you may have side air bags in the seats.

The ABS ECU is mounted between the LHM tank and the fuse box (which is just behind the battery)

The climate control ECU is up under the dashboard somewhere, I'm not sure exactly where or the best route to access it, but someone else will know.

That's all the main ECU's. There are also a couple of small ones like the dipping rear view mirror ECU etc but I wouldn't be so concerned about them - engine, gearbox, Hydractive, ABS and CPH are the expensive and critical ones to protect. As the CPH and engine ECU are coded together and difficult to replace individually you REALLY don't want to damage either of those.

[Hell Razor5543]

As far as I am aware, the main airbag ECU is under the trinkets tray (well, it is on Gracie), while the side airbag ECUs are low down within the central door pillars (just above the inertia reels of the seatbelts). I know about the side ones as I had to replace the nearside one on Gracie.

[Mandrake]

Thanks for that, I wasn't too sure about the airbag ECU's as I've never had reason to touch them or go looking for them.

[sparksie]

Great!
Thanks for that.
I don't have all of those, but I have more unplugging to do than I anticipated.
Glad I asked!
Now I need some settled weather. All this wind will blow away my MIG gas...

[sparksie]

Right
Got the offside fabricated and welded back together today, in nice bright sunshine.
Then I went over to the nearside and found I have a different problem over here.
I have a 3" to 4" wide strip of blisters extending vertically from the wheelarch almost to the top of the rear wing. I pricked one of the blisters and it was full of water.
This accounts for the large quantity of rust flakes found in the buttress section, despite the relatively much sounder condition of this side. The wing is obviously little more than paint, at this point.
I can't understand how I missed this when first assessing the car.
This being a highly visible part of the car, I'm not going to fix it in the middle of Winter, out in the open.
Therefore, reluctantly, I'm putting the car back together without carrying out any repairs to the nearside.
It'll be so much easier to do the buttress with the wing out of the way, not to mention the danger of setting fire to fresh waxoyl, if I do the buttress now and then attack the wing in the summer.
I can scarcely believe what I'm finding on a car that's less than 14 years old.
My 29 year old Volvo needs far less welding than this and is more enjoyable to work on, yet I'm doing the Citroen and disrupting the workshop in the process!
What is WRONG with me???
They're coming to take me away, ha ha...

[Mandrake]

Strange, because the Xantia in general is incredibly rust resistant. Mine is 15 and despite some scratches and scrapes on the paint work there is no rust on the body work at all, even in the door shuts and wheel arches...

I think you're just unlucky...

[sparksie]

Ah, that's what you think!!!
You just wait until you have to look in a place you don't normally see.
Mine seemed immaculate when I brought it in the first day, almost a month ago.
Everyone commented on how good it looked, but look what I found in the hidden bits!
I think it's devious, not to mention undeniably feminine.
It's getting under my skin, in spite of all logic suggesting it shouldn't.
I have long legs and short arms, which means I can't find any comfortable driving position, with both wheel and gear-lever being out of reach when I put the seat far enough from the pedals to avoid crippling myself.
The design, despite looking rather good, in an Austin Princessy sort of way, is still very much of the "Oh look, it fits. We'll make it like that then!" school of design, unique to the French.
The upholstery and plastics are, being polite, rubbish and the switchgear is appalling, while the wiring it's attached to is barely adequate.
I just know I'm going to be spending nearly as much time under it as in it, for the foreseeable future.
But, and it's a big BUT, I'm figuring out how I'm going to fit it in, not how I'm going to chuck it out.
I've sent better BMWs and VWs to the crusher, with no regrets, so why not this?
I'm only half joking when I wonder about my sanity!

[lexi]

I agree with much you say Sparksie.
They are likeable though. A bit like Land Rovers. Cr**P but strangely quite good.

[lexi]

Any pics of the rot?

[sparksie]

Hi Lexi

I didn't think of taking a pic before breaking out the angle grinder, sorry.
I did take one of what I'd cut out and one of the new patch in place, for my collection.
I can't see any intuitive way to post pictures on here, though I've seen others have been able to.
I'm not subscribed to any on line picture hosting sites, so I can't upload them and post a link, as suggested by some members.
I did read, in an old post in the archive, that posting images above a certain size was frowned on, due to data consumption/speed issues.
Pity, because a picture often explains better than any amount of words.
Not sure I really want to post a picture of my repair, mind. It was done outside in the yard, between the showers and gusts of wind! The welding suffered from lack of shielding gas a few times, when I didn't react quicly enough to the draught. The resulting burn-through and refill with MIG wire looks a bit of a mess and is not typical of my work. As I said, I wasn't expecting it to ever be seen, so I didn't try too hard, especially with the gravel eating my knees and back.
This is how I used to work thirty years ago, as a teenager, outside my parents house, or my mates parents house, depending on where we were least unwelcome. Since having access to smooth concrete and a pit, or occasionally a lift, I've grown soft and I've lost a lot of flexibility. Something the others are enjoying pointing out to me as I grovel under what they have christened "the skip"!
The weather has been atrocious for the last few days, so the Citroen has been stuck out the back waiting for a chance to come inside and get its bumper back.
It'll have to happen soon, because the test runs out in March and I want to put it in early, so I can deal with any issues before the current test runs out.
Given my profession, there's not much leeway for driving a car with an expired cert and none at all for allowing others to drive it!
I understand about the Landie. There's no such thing as one Land Rover, is there? It's always at least two, often more, just to have one road worthy!
There are a lot of them around here, in rural Ireland!

[lexi]

You might like the old Xantia once sorted up. Can raise the suspension and tow a boat over rough ground. Run on veg oil or other "stuff"
I had the Xantias and the 61 Landrover over to Galway area on many a fishing trip......great days around Corrib and Mask.

The welding outside..........a lovely job for about June with the Hawthorn out!