In the case of petrol engines, it is best to start by using handbrake, lifting the front part of the car on axle stands, and placing it on axle stands. Take the undershield out of the engine compartment, then unscrew the nuts to disassemble the exhaust downpipe off of the exhaust manifold, be it on an axle stand and retrieve the gasket. The next step is to unscrew the nuts and take off the hot air shroud off the exhaust manifold, and unscrew and remove the oxygen sensor, where necessary. In ACE and AAA engines, un screw the union nut, and unbolt the CO extractor pipe to the exhaust manifold. Gradually loosen the mounting nuts, take out the washers and take the exhaust manifold out of the cylinder head, reclaiming the gaskets and recording the position of the inlet manifold supporting brackets. On the AAA engine, divide the two parts of the exhaust manifold in a manner by unscrewing the clamp bolts, then removing the clamps, connecting the pipe, and the corrugated pipe. Wipe the mating surfaces of the manifold and cylinder head, find new gaskets on the studs, and on the AAA engine, clean the inner ends of the two portions, re-assemble them, and loosely screw the clamp bolts. Install the exhaust manifold, screw the mounting nuts to the set amount of torque, clamp the AAA engine mounting nuts to the full extent and install the CO extractor pipe, having screwed the union nut and mounting bolt. Install the oxygen sensor in place where needed, screw it in to the required torque, and reinstall the hot air shroud and exhaust downpipe, screw the nuts to the required tight before re-fitting the engine undershield and then lowering the car to the ground. In the case of diesel engines, especially when it is equipped with a turbocharger, the turbocharger and the exhaust manifold should be taken out to enhance easy access. Start with the application of a handbrake, lifting the front of the vehicle and placing it on stands that are supported on the axles. To separate the exhaust downpipe and turbocharger or exhaust manifold, cut off the undershield and unscrew the nuts which retain the downpipe to the axle stand and retrieve the gasket. Detach the vacuum hoses, air inlet hose, and the union nuts to the turbocharger, detach the oil supply and return pipes, unbolt and unscrew the oil return pipe at the crankcase and reclaim the gasket. Screw the mounting nuts out, one after the other, take out the washers, and take out the exhaust manifold of the cylinder head, and retrieve the gaskets. Should it be necessary, loosen the mounting nuts of the bench to take off the turbocharger and salvage the gaskets, then dispose of the nuts as new ones will have to be replaced. Wipe the mating surfaces of the manifold and cylinder head, find new gaskets on the studs, and reattach the turbocharger to the manifold with a new gasket, screwing the new mounting nuts to the required torque. Re-fit the manifold to the cylinder head, nutscrew to the recommended torque, and reconnect the oil supply and return pipes with new O-rings/gaskets, screwing the nuts and bolts to the recommended torque. Lastly, install a new gasket on the exhaust downpipe between the turbocharger or manifold and the exhaust, reattach the nuts to the correct torque, replace the undershield and drop the car to the ground.