jsa4

I have a '98 A4 quattro. Recently ordered a supersprint exhaust and downpipe. But was told that if I remove the catalyst and install the downpipe the second O2 sensor would trigger the check engine light. I'm planning on installing an APR ECU in the near future, but would like to know if the stock ECU is programmed to give any performance loss once the check engine light comes on, or does the light turn on and nothing else is affected. Since I bought the exhaust first I will install the exhaust and would have to run the car with the stock ecu for a couple of months.

Clark@turbo5.com

The bank 1 2nd O2 after the TWC is only there for emissions. If you run without a cat The ECU will throw a DTC that reports "Main Catalyst threshold exceeded". The Check engine light will come on to signal the error. The car will run as normal as the ECU does not use the rear o2 sensor for mixture purposes.

Just an annoying light and the fact that you are not smog legal is the only downside that I can see to running with no Cat. I do not know of a chip that has this feature disabled. It can be done in the programming but most chip tuners do not want to mess with the emissions side of things.

I personally would rather run that Catalyst as they do help our environment. The 5-10hp you may gain is not worth that to me.


Thanks

Clark

jsa4

Thanks a lot for your response Clark

DrHandball

Just a suggestion, perhaps you would like to run a high flow cat. These help accomplish both goals of increased performance while maintaining a smog legal car.