The FTO V6 system, apart from the 2 cast iron exhaust manifolds, comprises of 4 sections, a single Y shaped downpipe - this is the section with 2 flexy joints which joins the exhaust manifolds to the single oval section catalytic converter. The catalytic converter is the part of the system that converts, through catalytic reaction involving a precious metal, poisonous carbon monoxide into a more benign combination of carbon dioxide and water vapour.
The lambda or oxygen sensor is attached to the rear of the downpipe via a threaded boss. This sensor constantly 'sniffs' the oxygen levels in the car's exhaust gasses and sends the appropriate signal to the ECU, which then alters the air/fuel mixture accordingly. If the lambda sensor malfunctions, you may not notice the problem in normal running, but it may well cause problems with the MOT emissions test, not to mention economy. Similarly any cracks or splits in the downpipe assembly upstream of the lambda sensor can result in the sensor generating false signals to the engine ECU which can, in turn, affect engine performance and economy.
The lambda sensor is not to confused with the other sensor that is fitted to the FTO's exhaust system, which screws to the catalytic converter itself. This is the cat malfunction sensor which connects to a red warning light on the dash. This is a Japanese requirement and is simply a warning that the cat has malfunctioned in some way (usually because of an excessively rich mixture) and as it has no effect on the running of the vehicle otherwise, it can be disconnected with only one consequence. Removal of this cat failure sensor will trigger the red warning light on the dash and you will need to modify the wiring, a simple loop I guess, or as I normally do, remove the offending bulb from the instrument assembly.
From the cat back there is a centre pipe which includes a single expansion box. The last part is the rear silencer assembly which connects to the centre pipe just in front of, and above, the nearside rear trailing arm. The standard rear silencer assembly is finished with polished twin round tailpipes. The exhaust systems on non-MIVEC engined models such as the GR ,GS and GX are a smaller diameter than the GPX versions and thus parts are not interchangeable. Obviously the GS with its 1.8 4 cylinder engine has a different front pipe arrangement, but thereafter it is similar to the GR system.
The two parts referred to in the paragraph above, that is to say the centre pipe and the rear silencer assembly, are often referred to as a 'cat back system'.
Replacing exhaust parts
The main areas of failure are the flexy sections of the downpipe, and the joint between the centre pipe and the rear silencer assembly. The catalytic converter is pretty robust but they are now starting to fail - either due to general wear and tear or from impact damage. In extreme cases, or where the cat has been removed altogether, this may cause problems with the emissions part of the MOT test.
Good news! Decent quality replacement exhaust parts are now available, and are a cost effective alternative to the dizzyingly expensive Mitsubishi dealer components.
Another alternative is the stainless steel option from the likes of Mongoose. Excellent quality and fit, with the added advantage of guaranteed long life, Mongoose systems have a pleasantly sporty, but certainly not offensive exhaust note.