The active Carbon Canister Vent Valve (fuel tank vent valve) allows fumes from the fuel tank to be routed back into the air inlet manifold. This provides a means to safely handle petrol tank fumes and be kind to the environment. Introduced in 1993 so all V6 Calibra's feature this. The Motronic ECU controls the operation of a vent valve which opens a path from the fuel tank vent, via the active carbon canister, to the main inlet manifold. The ECU will generate a fault code if the vent valve fails to operate as expected. A fault with this system will not effect engine running or performance.
vent valve photo
vent valve feed to manifold
located in drivers wheel arch
Exhaust Gas Recirculation (EGR) is not used on the V6 Calibra (early or late).
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The Secondary Air Injection system (SAI) allows fresh air into the exhaust system. Commonly used to help the cat reach optimum temperature quickly on cold starts. It improves the oxidation of both hydrocarbon (HC) and carbon monoxide (CO) emissions, and reduces the light-off time of the catalyst. The secondary air injection system uses a small electric air pump (with air filter which should be periodically cleaned), a vacuum operated secondary air combination valve and an electronic secondary air switchover valve. The switchover valve is the one with the wiring connector at the bottom. This is controlled by the Motronic 2.8 ECU (pin 23). The Secondary Air Injection system was added in late 1996 and marked the third generation of V6 Calibra ECU (has KC identifier marked on ECU sticker) - a revision in the ECU code was required to support it.
The Metallic Monolith Catalytic Converter (or just Cat for short) is installed in the exhaust system. It's purpose is to reduce hydrocarbon emissions in the engine exhaust stream. This is a legal requirement for most countries and is a requirement to pass the M.O.T. in the UK (all vehicles post 1993). V6 Calibra's use metallic based Cat internals; this has an advantage over ceramic based cat internals in that metallic monolith types offer less restriction to exhaust back pressure making them more free flowing. Ceramic cats are cheaper to produce than metallic cats.
The standard stock exhaust system has been specifically designed to include a Catalytic Converter. The stock V6 Cat can last in excess of 150,000 miles (depending on how the engine has treated - i.e. allowed to warm up properly before booting it). Signs of failure will include a rattling sound from the Cat as the internals start to collapse. Depending on the severity of the Cat collapsing you may also notice a very significant reduction in performance once you reach mid revs. The car will feel like it's very much holding back past 3000 rpm.
Removing the Cat from the exhaust system (referred to as 'de-catting') and replacing with a straight through pipe will indeed reduce the overall restriction present in the exhaust. On a V6 Calibra this will result in a gain in peak bhp output of around + 3 to 5 bhp. However, if the stock restrictive manifolds and flexi joint are still used, you will see a reduction in the mid range engine torque curve due to a lowering of the exhaust temperature profile caused by removing the cat.
In summary, 'de-catting' a V6 will gain you 3 to 5 bhp at the peak top end. However, de-catting also causes a significant reduction in mid range torque making the car feel slower in the mid rev range. Because of this de-catting the V6 is generally NOT RECOMMENDED for most applications.
Sports Catalytic Converters are becoming a popular option to replace the stock item. These provide less restriction while maintaining the exhaust temperature profile and reducing emissions to acceptable levels. As these sports cats are around the same price as a replacement stock system they are highly recommend.