If I want to install a O2 sensor to monitor the air/fuel ration which exhaust header should I drill and weld a bung to or does it matter? Thanks for your response.

I always do mine at or downstream of the collector on a 4-1. What exhaust do you have?

placement is pretty important.
depending on which brand you use of system, you should follow the bung placement they recommend....


we have done about 3 bungs on different cars and always capture one bank but after the individual cylinders collect together on that bank.

(pre- muffler)

Clarification - I should have mentioned it's a dual carbed 1.7 with stock heat exchangers going into a Bursch(sp) extractor.

i put mine just downstream of the collector.... i could snap a photo if that would help.

I put mine in the last of the 2-1 collectors before the muffler when I had the Bursch. You need to make sure the orientation of the O2 sensor is correct. Most want to be as close to vertical as possible...

You don't want it on the bottom (6 o'clock), condensation will collect on the sensor and,wear it out quickly. You also might knock it off if you bottom out...

Thanks for the reponses, think I've got it figured out...now if I can just remembers where I stached that weld in bung...