GROSS Polluter= Yipes!!!!

[Ralpho40]

Help, first time for this 93-525i went on "rollers" for emission testing. It failed very badly on HC and NO. It does have 132K miles, has good power and idles well. Any ideas before I spend mucho $ at the "shop"?? Thanks for any replies. RalphO

[jeffreyb4me]

if it's running well and the 'check engine' isn't on it sounds like the Cat. converter has failed but even with this it wouldn't fail BADLY. the high HC&NO sounds like an air leak problem and a good place to start but still the idle should be fairly poor.....how are the sparkplugs?

[Ralpho40]

Originally Posted by jeffreyb4me

if it's running well and the 'check engine' isn't on it sounds like the Cat. converter has failed but even with this it wouldn't fail BADLY. the high HC&NO sounds like an air leak problem and a good place to start but still the idle should be fairly poor.....how are the sparkplugs?

First thing, I thank you for the reply. The idle is very good, steady and somewere around 550 and there is no 'check engine' light. The MPG however is not so good, it has been much better in the past.
The car is serviced by a BMW?Porsche shop. Every year it goes in for a check up. The owner is well versed in BMW repairs and that equals $$.
The failed test was in CA, the HC (PPM) MAX value is 83 the AVE value is 21 and the measured value was 171. The NO (PPM) MAX value is 689 the AVE is 150 and the measured value was 912. The CO (PPM) is 0.48 the AVE is 0.06 and the measured value was 0.49. To me, it seems like a CAT problem. Would replacing the CAT with a non-BMW part have a bad effect on the vehicle's computer, e.g. different exhaust back pressure???? Could a bad Oxygen sensor have this effect?