I want to put a test pipe on and I will need the o2 simulator to keep the CEL off. Will the o2 simulator keep my A/F gauge from working correctly?

 

You should be using the signal from the stock O2 sensor that is in the header if you are using a narrow band type gauge. If you are using a wide band type of gauge, then it should have come with its own O2 sensor that you should have mounted in the header in addition to the stock sensor. The presence or absence of a cat won't affect what the sensors in the header sees. If you are using the sensor in the cat (subsequently in the test pipe afterwards), your A/F would be off before and after the cat's removal.

 

I have a basic A/F gauge that uses the stock sensor. Does it read from the primary sensor in the header or the one in the cat?

 

It "should" be reading from the primary sensor (in the header). Where yours read from, only you (or the person who installed it) know for sure.

 

I used the solid white wire off the ecu so I think it is the primary. So im ordered it today!!!

Thanks

 

You'll be fine.