1996 Saab 900 Q&A
1996 Saab 900 Question: emission failure
Too rich can be due to so many things. An engine out of tune, too high a fuel pressure (bad fuel pressure regulator), fuel injectors that are not atomizing fuel spray properly, ignition misfire due to weak spark or bad spark plugs, restricted air filter, or an emission test may "show high CO" if the catalytic convertor is not neutralizing the harmful exhaust gasses emitted from the engine/ - patrick mannion
The Exhaust Gas Recirculation (EGR) Valve can fail, which also causes EGR distribution valve failure. The Check Engine Light may illuminate and there will be excessive exhaust noise.
The exhaust flex pipe can fail causing excessive exhaust noise from the front/center area of the vehicle. The flex pipe is a flexible joint in the exhaust that allows for engine movement.
The exhaust center muffler can fail causing excessive exhaust noise.