O2 sensor placement

[Mr. Goatman]

I have been reading about placement and it seems that the sensor needs to be behind the collector so it gets all of the exhaust. My Cat converter is right behind the Y and it has a bung on the back end of it. Can I use the bung on the Cat for my O2 sensor?

[Bill usn-1]

Well it depends...there are a lot of factors to consider.
If you have to pass emissions then it needs to warm up quick so it either needs to be closer to the engine or you should run a heated O2 like a 3 or 4 wire O2.

If you don't have to pass emissions then it comes down to your personal preference.
The further back you place the 1 wire O2 the longer it takes to warm up to go into closed loop and the quicker it cools down.

Now, what does that really mean to you....nothing really. your engine if properly tuned will run the same whether it's in open loop or closed loop.

But in O/L the system can't perform the small fine tuning it does based on the O2 level in the exhaust.

So, the easiest thing to do is just use the bung you have and run a 3 or 4 wire O2 so it uses 12v power from a relay to help warm it up when you first start.

Another factor is the delay in the bin file to account for how far back the O2 is placed so the ECM has an idea of when it was rich or lean.

So...now we either need to place the sensor close to where it was from the factory, or you will need to play with the O2 sensor setting to account for the farther distance away from the engine.

So if your using a bin like the ASDU or ASDX then you may want to check the service manual for that vehicle...1991 1500 PU, and see how far back the O2 is placed.

Either way it has to be before the CAT not after it.

[Mr. Goatman]

the sensor I bought is a 4 wire. The bung is IN the cat. So, It sounds like I should drill/weld a new bung a little farther upstream.

[sgtpoliteness]

As long as it's BEFORE the catalyst portion of the cat housing you should be golden. Then, as I need to do, it's a matter of setting decay in the PCM bin.

Only OBD2 cats should have a 'post-cat' (or, in OBD2 terms a S2 sensor). All that sensor does is monitor cat efficiency. We tune those out on a regular basis for high performance files.

[FSJ Guy]

As long as it's BEFORE the catalyst portion of the cat housing you should be golden. Then, as I need to do, it's a matter of setting decay in the PCM bin.

Only OBD2 cats should have a 'post-cat' (or, in OBD2 terms a S2 sensor). All that sensor does is monitor cat efficiency. We tune those out on a regular basis for high performance files.

What he said.