Changing the driveshaft boot

With the roadwheel still in place, remove the wheel nut securing pin and the crown, then loosen the wheel nut (the one on the CV joint) about a quarter of a turn or so, just enough to get it going. Applying the park brake or even the foot brake (assuming the system is still under pressure) will help. Loosen the wheel bolts slightly, then release the park brake.

Air Conditioning

There are several cabin temperature control systems fitted to the various models.

What is "Climate Control" (on a P reg, 1996 XM TD 2.5) as opposed to Air Conditioning?

There were several 'climate control' systems fitted to the XM. In fact, IIRC the manual refers to them all as 'climate control'. Onseries 1 there was:

1) Manual
2) Semi-auto (looks very similar to manual)
3) Full auto

1.5) Later series 1 also came with manual but separate for driver and passenger side.

Exhaust system

You can delay the corrosion if you use stainless steel exhaust components. For instance, Walker, a widely known aftermarket manufacturer of exhaust parts has a family named Aluminox. These parts are made of stainless steel and covered by a layer of aluminum alloy. The estimated life of these exhaust components exceeds five years under normal use while their price is only about 30% higher than that of the standard components. The last time I asked it was only available for the diesel models.

Fuel injection basics

Citroën used various systems of two manufacturers, Bosch and Magneti Marelli. All those systems operate on very similar principles so troubleshooting them involves more or less the same steps.

There are two basic categories: fuel injection (EFI) and engine management (EMS). EFI systems, as their name implies, are responsible for the injection of fuel only, the ignition sparks are created using traditional methods (a breakerless distributor). EMS systems, in contrast, govern both fuel injection and ignition themselves.

Stroboscopic timing light

Traditionally, stroboscopes were built with xenon flashlights such as those used in photographic flashguns. However, these flashlights require a 400-600 V voltage and even more for igniting them. Needless to say, electric shocks of such voltages are often lethal. Unless you have experience in building such high voltage circuits (including proper insulation) and also have measuring equipment to help with the process, you shouldn't even think of building one.

Fuel cut-off valve

It usually dies either when you (try to) start the engine or when you stop it, rarely while it's running. The engine will not start because it will not be getting any fuel. The reason is usually overheating and deformations in the coil whichresult in the valve plunger getting stuck, or internal shorts or open circuits (due to heat) in the coil.

Turbo Diesel Failure

Clean combustion resulting in clean oil (assuming it has the proper grade, not some cheap concoction) is essential not only for the engine but for the turbo as well. Most people are not aware that a turbo can be--and actually should be--cleaned every 150,000 km or so. This procedure will make it last forever.

Diesel Engine Care

Most people are not aware that the main reason a diesel engine wears out is improper combustion, usually caused by worn out injectors, improper timing, or simply lack of air (influenced by several factors, one of which may simply be a dirty air filter). Anything which produces soot (eg. particulates), including the "black smoke" effect, results in particulates ending up in the engine oil. This soot then accumulates in areas where oil flow is low, like behind the piston rings. As the deposits grow, the ring is being forced outwards.

Diesel Combustion

A lot of things happen at the moment the fuel is injected. If the fuel was somehow perfectly microscopically atomised on injection, it would not self-ignite at all. It would have trouble igniting even with a spark plug. Ignition needs a richer fuel-air mixture, and this is locally provided by the start of the injection being full of larger drops of fuel, because it occurs at a lower than maximum pump pressure (about 2-3 times lower). The evaporation of components from the fuel as it enters the hot compressed air is what makes it ignite.

Diesel Basics

Diesels are taken for granted in 99% of all cases--the truth is, most of them can take an incredible amount of "just driving", but the neglected maintenance results in slow decay. However, even engines treated extremely poorly can easily run 100k miles or more.

Most people come to a diesel from a gasoline car, and apart from the obvious differences, they do not realise how different the engine really is. Although it is very similar mechanically, the basic pricinples are very different.