Can someone give me a definitive answer about whether or not I need to have both LT1 O2 sensors plugged in? I did some searches and came up with conflicting views. One thread I read stated that the second O2 sensor was just for emissions, in which case I will not need it, since I am not running a cat. The headers I got only have one 02 sensor bung installed, and I would like to answer this question before I install them.

I have also seen O2 sensor simulators that plug into the O2 sensors, but all the ones I have found are for OBDII systems, and my motor is OBDI out of a 94 vette. Any help would be appreciated...

 

As far as I can tell you need the second one, but not the third and fourth ones. If your wiring harness is pre 1996 you should not even have places for the third and fourth sensors. I know for a fact that you cannot program out the second O2 sensor with any of the current tuning programs. This means the motor will never go into closed loop, and you will waste gas/power. I had a second bung welded into my y-pipe since my headers were Jet-Hot Coated. Cost me $60 at meineke, probably a rip off considering the not so straight welds, and the exhaust leaks from other places that followed, but at least I have the 2nd O2 sensor now

Bottom line: 2nd O2 Sensor required for closed loop operation (extremely highly recomended) third and fourth O2 sensors, get dummies if you have an ODBII system, otherwise leave 'em.

 

BTW the cheapest weld in O2 bung I found was a Holley unit. Cost about $10. About 1/3 the price of the others and the exact same thing. Drill a hole in the y-pipe and MIG/TIG weld-er in.

Why would you want to have only 1 sensor anyways? You'll loose fuel tuning accuracy from bank to bank with out it!!

 

Is the y-pipe the right place to weld in the second bung? The original first O2 sensor is on the driver's side header.

I think I read the second O2 sensor is supposed to be mounted on the cat itself, would this matter?

 

If you have OBD I, you have 2 sensors. One on each bank of cylinders. It is labled that way right in the wiring diagram. The sensors are also heated electrically ie they are 3 or 4 wire sensors, 4 in this case. the location should be as close to the engine as possible, like in the header collector or y-pipe on a set a shorties.

if you have OBD-II you have 4 sensors. 2 in each bank, same as OBD-I, and 2 more, one after each cat. These are the emissions o2 sensors you can 'trick' with a fake sensor.

Hope this helps

 

You should have both sensors for the engine to run properly. I am 98% sure that on the Vettes one sensor is in the manifold and one is in the pipe right before the cat. As the cats are so close to the manifolds the cats are actually before the Y pipe. Moving the cats so close to the engine is how the get away without having to plum the air pipes into the cats.
I second the notion of having the sensor isntalled as close to the motor as possible although with the new heated ones it isn't as critical.

 

For proper PCM tuning, I was told that they should be at the exact same point on each header(or y-pipe). I can't remember who told me this...probably Ion at www.madz28.com.

 

I was running only one and my car ran like crap. I installed the second one and it's much much better. My gaz/milleage went way up.