Dual exhaust O2 sensor (s)?

[Fugly78]

Been thinking of aftermarket EFI on my project. Since I am still learning about what is needed, one thing that kept coming up for me was the O2 sensor. Most of the projects on any vehicle forum I find talk about the sensor going after the collector or in the case of dual exhaust, don't mention it at all. It seems to me that if the O2 sensor will help the computer determine if the mixture ratio is correct when injecting, then it would affect the mixture ratio based on each cylinder or at least per engine side which would then affect the resulting sensor on each side of the exhaust. Is this correct?

So, am I overthinking this or does it work that way? Would there need to be two O2 sensors, one for each side of the exhaust? I haven't seen any kits out there for two sensors.

Trying to figure this out, so any experience would help.

[Stuka]

This all depends on the vehicle and ECU used.

My Wrangler for instance has four O2 sensors. Two before the first set of Cats, and two between the first and second set of Cats (It has four Cats).

Some ECU's only use an O2 sensor before the Cats, some have them before and after. There are some that use three. One before Cats on each bank, and then after they combine to one exhaust.

[AwesomeJ10]

I'm experienced with running/tuning the 1227747 ECM that was found in late 80's early 90's GM trucks.

They only had one o2 sensor on the passenger side exhaust manifold.

[Bill usn-1]

The engine design and the EFI system determines the O2 use.
For the older TBI system the data rate is about once a second. For the newer sequential MPFI with coil on plug ignition the data rate is hundreds of times per second.

For our older designed engines you can realistically only reach a certain efficiency.
Keep in mind that all EFI developments were for emissions. that's how MPFI got it's start.

Most of the stock manifolds are dual plane design so you have 2 cylinders on each side of the engine fed by 1 of the injectors or half of the carb. The center 2 on one side connect to the outer 2 on the other side.

So by using 1 O2 it is actually monitoring each side of the throttle body.

Placement is also discussed a lot. If your tune is not very close then the closer you mount it to the manifold the faster it will heat up and go into closed loop or you can use a heated O2.
If your system is tuned then you really don't even "need" the o2 sensor.
Keep in mind you never had one with a carb and it ran.
The O2 simply provides feed back to the ecm so it can fine tune your tune to compensate for changes in temp and altitude and a dirty air filter.

Other considerations are the farther the o2 is from the engine the longer delay there is in the feed back to the ECM.
You realistically should mount the O2 about the same distance from the engine as it was from the factory or you need to adjust some of the setting in the chip to match.
Not a big deal but it all helps.

[billygoat]

Most aftermarket will have 1 - use a heated style to compensate for distance from the manifold, and the ideal location on dual exhaust would be in the crossover pipe between them.

If you are not running a crossover pipe for some reason, then stick in on the passenger side (most common) and don't worry about it, it will be fine. I had mine just under the pass manifold (non-heated), and went to a heated just after the Y pipe and I so no more change in my tune than you see on a rainy day vs a sunny day.
I will say the heated did put it in closed loop faster.

[DarkMonohue]

Most aftermarket will have 1 - use a heated style to compensate for distance from the manifold, and the ideal location on dual exhaust would be in the crossover pipe between them.

If you are not running a crossover pipe for some reason, then stick in on the passenger side (most common) and don't worry about it, it will be fine. I had mine just under the pass manifold (non-heated), and went to a heated just after the Y pipe and I so no more change in my tune than you see on a rainy day vs a sunny day.
I will say the heated did put it in closed loop faster.

A heated sensor will definitely be beneficial if the sensor is any significant distance from the cylinder head. If the sensor is located within the exhaust manifold, it'd be less critical.

I don't think locating the sensor in a crossover pipe (a.k.a. balance tube) would be a good idea. You do not have steady flow through those. Makes more sense to put the sensor out in the main exhaust pipe, even if that means you are only sampling half of the engine's cylinders. That's well within the "close enough" tolerances we need.

[Stuka]

Most aftermarket will have 1 - use a heated style to compensate for distance from the manifold, and the ideal location on dual exhaust would be in the crossover pipe between them.

If you are not running a crossover pipe for some reason, then stick in on the passenger side (most common) and don't worry about it, it will be fine. I had mine just under the pass manifold (non-heated), and went to a heated just after the Y pipe and I so no more change in my tune than you see on a rainy day vs a sunny day.
I will say the heated did put it in closed loop faster.

A heated sensor will definitely be beneficial if the sensor is any significant distance from the cylinder head. If the sensor is located within the exhaust manifold, it'd be less critical.

I don't think locating the sensor in a crossover pipe (a.k.a. balance tube) would be a good idea. You do not have steady flow through those. Makes more sense to put the sensor out in the main exhaust pipe, even if that means you are only sampling half of the engine's cylinders. That's well within the "close enough" tolerances we need.

Yeah I agree. An H pipe is just meant to increase savaging, it does not have constant flow and would be a poor place to put it. Having it on one side, close to the manifold is fine. Not as accurate, but close enough to function without any real issues.