1. Disconnect the wire from the negative terminal of the battery.
2. Remove the engine crankcase guard (see "Removal and installation mudguards and engine crankcase protection").
3. Squeeze the HO2S diagnostic harness connector retainer and disconnect it from the engine harness connector.
4. Unscrew the three nuts securing the intake pipe flange to the exhaust manifold flange...
5. ...separate the flanges and remove the gasket.
6. Unscrew the two nuts securing the flange of the inlet pipe to the flange of the additional muffler...
7. ...and remove the exhaust pipe.
8. Remove the sealing gasket from the studs of the rear flange of the inlet pipe.
WARNING: Front gaskets...
...and replace the rear flanges of the intake pipe with new ones each time the connection is disassembled, since tightly compressed gaskets will not provide a reliable seal.
9. If you are replacing the downpipe and the new pipe does not have an oxygen concentration sensor, unscrew it from the removed downpipe and install it on the new unit.
10. Install the exhaust pipe and all removed parts in the reverse order of removal.
[The original text can be found on the website: CHEVYMAN.ru]