Front Exhaust Pipe With Catalytic Converter
Front Exhaust Pipe With Catalytic Converter (B204i)
Dismantling
IMPORTANT
The exhaust pipe's flexible section is highly sensitive to bending and must not be bent more than about 5°, as this could result in permanent deformation.
Do not allow the catalytic converter to hang from the flexible section.
1 Remove the heat shield over the exhaust manifold.
2 Unplug the oxygen sensors leads, undo the clip and cable clamps.
IMPORTANT
The leads must not be twisted. The oxygen sensor is sensitive to knocks and blows and must be handled with care.
3 Unscrew the upper nuts at the joint between exhaust manifold and front exhaust pipe. Raise the car.
4 Remove the oxygen sensor.
5 Loosen the joint between the front exhaust pipe and the middle pipe.
6 Undo the remaining nuts at the joint between the front exhaust pipe and exhaust manifold.
7 Remove the two rubber mountings between the catalytic converter and engine subframe
8 Lower the front exhaust pipe.
To fit
IMPORTANT
The exhaust pipe's flexible section is highly sensitive to bending and must not be bent more than about 5°, as this could result in permanent deformation.
Do not allow the catalytic converter to hang from the flexible section.
1 Clean the joints.
2 Fit the rubber mountings between the catalytic converter and engine subframe. If necessary, change the rubber bushes.
3 Position the front exhaust pipe and secure it to the exhaust manifold by means of the two lower nuts.
Tightening torque: 40 Nm (30 lbf ft)
4 Bolt the front exhaust pipe and intermediate pipe together, using a new clamp.
Tightening torque: 20 Nm (15 lbf ft)
IMPORTANT
To avoid leakage, use new clamps when tightening the joints.
5 Make sure that there is adequate clearance to parts next to the exhaust system.
Also check that the rear silencer's tailpipe is correctly positioned in the opening that is cut out for it in the rear bumper.
Fit the oxygen sensor, but first lubricate the threads with Molycote 1000, part No. 30 20 971.
Tightening torque: 55 Nm (41 lbf ft)
IMPORTANT
The oxygen sensor is sensitive to knocks and blows and must be handled with care. It is important to ensure that the connection between it and the nipple is gastight.
The oxygen sensor's lead must not be stretched between engine and exhaust pipe. Secure the cable to the clips so that a loop is formed just before the sensor.
6 Lower the car to the floor.
7 Screw on the upper nuts securing the front exhaust pipe to the exhaust manifold and tighten them.
8 Plug in the oxygen sensor's leads and fit the clip and cable clamps.
9 Fit the heat shield over the exhaust manifold.
Front Exhaust Pipe With Catalytic Converter (B204L/E/R)
Dismantling
IMPORTANT
The exhaust pipe's flexible section is highly sensitive to bending and must not be bent more than about 5°, as this could result in permanent deformation.
Do not allow the catalytic converter to hang from the flexible section.
1 Remove the heat shield over the exhaust manifold.
2 Unplug the oxygen sensors leads, undo the clip and the upper cable clamp.
IMPORTANT
The leads must not be twisted. The oxygen sensor is sensitive to knocks and blows and must be handled with care.
3 Remove the lower cable clamp and oxygen sensor.
Raise the car.
4 Loosen the joint between the front exhaust pipe and the middle pipe.
5 Unscrew the front exhaust pipe from the turbocharger.
6 Detach the exhaust pipe from the rubber mounting on the engine subframe and lower the exhaust pipe.
To fit
1 Clean the joints.
2 Position the front exhaust pipe and secure it to the turbocharger. Before fitting, lubricate the three studs on the turbocharger with Molycote 1000, part No. 30 20 971.
Tightening torque: 25 Nm (18.5 lbf ft)
3 Attach the exhaust pipe to the engine subframe with the rubber mountings from the catalytic converter. If necessary, use new rubber bushes.
4 Screw together the joint at the intermediate pipe, using a new clamp.
Tightening torque: 20 Nm (15 lbf ft)
IMPORTANT
To avoid leakage, use new clamps when tightening the joints.
5 Lower the car to the floor.
Fit the oxygen sensor, but first lubricate the threads with Molycote 1000, part No. 30 20 971.
Tightening torque: 55 Nm (41 lbf ft)
IMPORTANT
The oxygen sensor is sensitive to knocks and blows and must be handled with care. It is important to ensure that the connection between it and the nipple is gastight.
The oxygen sensor's lead must not be stretched between engine and exhaust pipe. Secure the cable to the clips so that a loop is formed just before the sensor.
6 Run the cable up, connect it and fit the connector in the holder.
IMPORTANT
Watch out for sharp edges and hot components.
Secure the cable to the turbo's coolant pipe, using a cable tie.
7 Fit the heat shield over the exhaust manifold.
Front Exhaust Pipe With Catalytic Converter (B235R)
Dismantling
When changing the front exhaust pipe, first remove the oxygen sensor (the rear one also in the case of OBDII) for fitting on the exhaust pipe. Before fitting the oxygen sensor, apply Molycote 1000, part no. 30 20 971, to its threads.
IMPORTANT
The leads of the oxygen sensors must not be twisted. Twisted leads are susceptible to vibration and the leads could fracture. Since the oxygen sensors are sensitive to impacts and shocks, they must be handled with care.
Tightening torque: 55 Nm (41 lbf ft)
1 Remove the bypass pipe with valve. Collect the O-ring where the pipe is connected to the turbo's inlet pipe.
2 Remove the exhaust manifold's heat shield.
3 Unplug the oxygen sensors connector.
In the case of OBDII, also unplug the rear oxygen sensor's connector.
Snip the cable tie securing the sensor's lead. Thread the lead through so that it runs freely.
4 Undo the 2 upper nuts on the joint between the turbocharger and the front exhaust pipe.
5 Raise the car.
6 Undo the lower nut on the joint between the turbocharger and the front exhaust pipe. (OBDII: remove the rear oxygen sensor's cable clip.)
7 Remove the clamp at the joint between the front exhaust pipe and the intermediate pipe.
8 Unhook the exhaust pipe from its rubber mountings and lower it away. Make sure that the leads of the oxygen sensors are not caught up or damaged when the exhaust pipe is removed.
IMPORTANT
The flexible section in the front part of the exhaust pipe must not be bent more than 5°.
To fit
IMPORTANT
The flexible section of the exhaust pipe is sensitive to bending and must not be angled more than 5° as this could lead to permanent deformation.
Do not allow the catalytic converter to hang from the flexible section.
1 Clean the joints.
2 Offer up the exhaust pipe and hook it onto its rubber mountings. If necessary, change the rubber bushes.
3 Fit the lower nut between the front exhaust pipe and the turbocharger. Smear the threads with Molycote 1000, part no. 30 20 971, or the equivalent.
Tightening torques:
4 Bolt the front exhaust pipe and intermediate pipe together, using a new clamp.
Tightening torques:
IMPORTANT
To avoid leakage, use new clamps when tightening the joints.
Make sure that there is adequate clearance to parts next to the exhaust system. Check that the tailpipe is positioned symmetrically in the space cut out for it in the rear bumper.
5 Position the oxygen sensor's lead and lower the car (OBDII: position the lead and secure it with cable ties).
Fit the upper nuts between the front exhaust pipe and the turbocharger. Coat the threads with Molycote 1000, part no. 30 20 971, or the equivalent.
Tightening torques:
IMPORTANT
Tighten the nuts alternately to avoid misalignment of the flange. The exhaust pipe's flange must not abut against the turbocharger's flange.
7 Bring up the oxygen sensors lead and plug in the connector. Secure the lead with cable ties.
IMPORTANT
The oxygen sensor's leads must not be twisted.
Make sure that the lead does not rest against hot surfaces or sharp edges.
8 Fit the exhaust manifold's heat shield.
9 Fit the bypass pipe with valve. Lubricate the O-ring at the connection to the turbo's inlet pipe with non-acidic vaseline, part no. 30 06 665, or the equivalent.