Turbo models with 4 O2 sensors?

[Patryn]

What does the ECU use the two O2 sensors in the downpipe for? Specifically a 1998 VR4 non-Cali spec.

[alottaboost]

it uses the rear o2's to determine if the catalytic converters are working properly. it's on all 96+ cars (OBD2 diagnostics). it's just for emissions control

[Patryn]

So as the only issue that I would encounter would be an engine code (check engine light) if I removed them and replaced with wideband O2 sensors?

[alottaboost]

Originally Posted by Patryn

So as the only issue that I would encounter would be an engine code (check engine light) if I removed them and replaced with wideband O2 sensors?

yep. you can always drill a hole in the downpipe and have someone weld an o2 bung in there for you.

[tachyon_ftl]

If you have enough money for two widebands, then look for a wideband setup that will also send out a 0-1 volt signal for the ECU. It's for just that purpose. The problem with the CEL is that in a lot of states, you can't pass inspection with one. If you can in your state, and you don't mind living with the light on the dash all the time, then you can delete the secondary O2s. You can also get an O2 simulator. Some simulators need to have the O2s present; they're used to avoid a CEL with gutted precats. Other simulators will in fact pretend to be real sensors and you'd need something like that.

Or, as most people do, just add a single wideband O2 sensor in the DP after the merge. You're not going to learn much more monitoring each bank separately with an O2 sensor. You can usefully add an EGT to each bank to keep an eye on how they're burning; it's easier to spot a high temp condition than to catch a brief lean O2 at WOT.