Cat bypass pipes

[funi]

Recently got 97 with cat by pass pipes now have code p0420/430 at times anyone how to trick the computer into thinking the cats are there I have heard about shimming the sensors out but no idea if upstream or downstream I do have the cats to Put back on

[very~worn~944]

The upstream o2's work the same, cats or not. The downstream o2's need to see a stable lean condition.
If you code the vehicle to ROW instead of USA it stops looking for the non-existent cats... So no CEL, but I'm pretty positive it won't pass emissions when the DME gets scanned.

[funi]

What do I need to change the setting in the ECM thanks for the reply

[Pbadore]

Originally Posted by funi

Recently got 97 with cat by pass pipes now have code p0420/430 at times anyone how to trick the computer into thinking the cats are there I have heard about shimming the sensors out but no idea if upstream or downstream I do have the cats to Put back on

On my US market 96 GTI VR6 2.8l engine which is operating in a third world country with bad fuel I inserted a spacer between the threaded O2 sensor fitting and the O2 sensor to move the O2 sensor out of the exhaust gas stream behind the catalytic converter. The spacer was custom made out of stainless steel and the check engine light for "cat below efficiency" has only come on 2 or 3 times in 6 years and about 80,000 miles. An Autozone scan tool scans off the fault code for months or even years at a time. Also the fuel economy improved as did the engine response. Some people use spark plug anti-foulers (usually two) of them to accomplish the same goal. An emission system in this condition will not pass a visual inspection and I am not sure if this modification will allow a "readiness check" to be completed for an emission test.

[funi]

Thanks I have heard the same but was told upstream sensors it makes better sense since I now know what sensor will trigger the code will try this this wknd I have couple machines that will read and clear codes thanks again

[Pbadore]

Originally Posted by funi

Thanks I have heard the same but was told upstream sensors it makes better sense since I now know what sensor will trigger the code will try this this wknd I have couple machines that will read and clear codes thanks again

You should read about the function of the O2 sensors on OBD2 engines. The upstream O2 sensors are used to adjust the A/F ratios and the downstream O2 sensors monitor
catalytic converter efficiency. There are many fault codes for both sensor locations.
The spacers are to fool the downstream O2 sensors into reading lower emission levels in the exhaust gases that exit the cats.

[funi]

Ended up using two antifoulers each side after 1000 miles no ck eng light thanks for all replies