O2 location

[nightglide]

Does it matter which header I put my o2 sensor?
And if does matter can you explain why?
Thanks
Owen

[DustinLangston]

Is it a TBI system?

[FSJ Guy]

Is it a TBI system?

Good question. Tell use what you're injecting and how you're injecting it. :- p

Although, unless you've got a super fancy MPFI with a crank position sensor, I think right after the Y pipe would be fine.

[Tatsadasayago]

One thing I learned after adding two wideband heated O2 sensors on my 77; The farther away from the manifolds, the less accurate the readings due to temps. Locating the sensor after the Y will do better at averaging the O2 count but tends to be less accurate. This is why most systems have a sensor at the manifold(s), downpipe and often a pre and post cat location. The sensors are designed to compensate for the temp differences.

[nightglide]

I'm planing tbi. Might be a while....but I need to replace all my header and collector gaskets so I wanna weld in o2 bung while I have them off. I already have a heated o2 sensor which I'm told I need for headers......

[Cataldo]

One thing I learned after adding two wideband heated O2 sensors on my 77; The farther away from the manifolds, the less accurate the readings due to temps. Locating the sensor after the Y will do better at averaging the O2 count but tends to be less accurate. This is why most systems have a sensor at the manifold(s), downpipe and often a pre and post cat location. The sensors are designed to compensate for the temp differences.

My experiences with widebands are very similar. It is also critical to keep the O2 sensor on the top half of the exhaust pipe if it is parallel to the ground. If you are running shorties or manifolds where the exhaust first goes down then back it is less critical, but still good to keep it on the 'top side'. This is to ensure moisture does not pool in the sensor. Also the further away the sensor is the longer it will take to warm up, especially with 1 wire narrow band sensors.

[tgreese]

I expect most of you would buy and use the Innovate Motorsports LC-2, if you bought a wide-band O2 sensor. The docs for this product gives instructions for mounting, which specify at least 24" downstream of the exhaust ports. Any closer is too hot. This would rule out mounting in the manifold, though if you have headers, mounting near the outlet flange should be ok -

http://www.innovatemotorsports.com/supp ... Manual.pdf

[Bill usn-1]

I have addressed this a few times here.
The GM TBI system uses a NB-narrow band O2 sensor. Most are the 1 wire located close to the manifold.
When going to a header it can be moved to the collector but should be on the header side and not the pipe side due to gaskets leaks.
Side does not matter.
Preferred to go with a 3 or 4 wire NB O2 sensor when located further from the engine.
It should NOT be located further back or the signal back to the ECM will be delayed and affect the tune corrections.

If the engine runs good then you "can' even install in just 1 cyl pipe and retain the 1 wire.
Keep in mind that the O2 sensor has absolutely NOTHING to do with how the engine runs.
Let me repeat this.
The O2 sensor does not affect how the engine runs....
IF
The tune is correct.
The O2 simply allows the system to make minor corrections to the tune due to temp and weather changes.

The WB-wide band O2 is only used for guys that do their own tuning and should not be used in simulated mode to run the factory EFI system.
It is not needed for 90% of all the conversions.
If a guy just likes to play with tune settings and watch the AFR on his dash as he drives, then they are fine.
You could also just install a vacuum gauge like in the 70's.
The higher the vacuum the better the MPGs.

Hope this helps with O2 sensor questions.

[Tatsadasayago]

Yanno what I noticed Bill;
With a carb and dual Innovate wideband O2 sensor setup, I found there is a place, on both ends of the AFR envelope where the O2 levels can be deceiving. A flooding/over-rich and a lean-out measures very similar. Since the sensor only measures the O2 in the exhaust stream, it can't tell the difference. When my HEI ignition module was in it's last death rattle, the AFR meter was showing an 8:1 ratio...which would lead one to believe the mixture was over-rich. In a way, that was true since the mixture wasn't being burned, but would lead one to believe the opposite. I would guess an ECU would come to a similar conclusion.

[Bill usn-1]

Yes you are correct.
Every misfire puts unburned fuel/O2 in the exhaust and the system will try to correct for it.
To take it a step further,
MPFI was developed as a way to meet the idle emissions testing when newer standards were implemented.
With fuel above the throttle blades like a carb and TBI, at low rpms, the fuel can coat the walls of the intake and cause droplets to form. At idle these droplets can break lose and cause a rich condition for that burn. This would cause a failure in the testing.
By placing the injector at the head it reduce the puddling and improved emissions.
The misconception is that MPFI improves performance or MPGs.
It really doesn't. It was the development of the engine design to take advantage of the new MPFI that led to increases in both.
Putting MPFI on an older engine will not see any real difference in either over a TBI system.
Some that convert from the early TBI ECM to a later/faster BI or MPFI PCM have found some improvements due to the faster computer making tuning and auto correction easier for them.
But the older systems can be properly tuned to give the same results.
It's all in the setup and tune.
Keep in mind that WOT is WOT.
As long as the same AFR and timing are applied the engine develops the same power with the same CFM used.

[Renodemona]

Been running for 2 years without the sensor at all. Starting to think I don't really *need* it, but I guess I should get around to doing it eventually. When it goes in, It will go in driver's side just downstream of the manifold. My understanding is that it gets data from both injectors as the intake runners draw from both sides if you pull from the whole bank (either driver's or passenger's).