Had a nightmare trying to reduce the CO emissions on my brothers astra x16 szr .
missfires, black plugs, coil pack fault codes,but seemed to be running fine ,
tested everything i could think of, replaced inlet gaskets,oil 15W40 mineral (not synthetic) ,breathers ,vacuume pipes,tested map,cts,egr, sensors,RESET ECU, live data on solus reader (NOTE you can not use obd2 elm327 on some mark 4 astras) ,ecu reporting everything is ok readings wise
found the injector was over fueling badly, not reported to ecu !
fortunately i have another brother with the same astra so could swap parts from one to the other to diagnose what was going on .
it had been to 3 diffrent garages ,who miss diagnosed it before i got my spanners on it , all said replace the cat .... er NO ! find the over fueling problem before you even think about sticking a cat on, (because anti freeze and overfueling can contaminate your cat and render it useless)
explains miss fires and coil pack failures,intermittant MIL lamps etc
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