Best placement for Wideband O2

[RYU]

I have a leftover AEM Uego from a previous build. However, I only have one. I know ideally the best way would be to run two WBs (one for each bank). However, until I can finalize my gauge situation (i.e. DGauge, DashDaq, AEM, Zeitronix, etc) i'd like to wire up this single WB temporarily.

Have a couple questions and would love your opinions please :smile:

1. In the NSX, which bank, front or rear, typically runs lean? It's my experience with V8s that one bank typically runs just slightly more lean. I'd like to place the O2 sensor on the leaner bank.

2. I'm in the process of building a custom valve actuated exhaust and will have the option to place an H-pipe that's about 2" long before the cats. If one was to place the WB O2 sensor in the middle of a 2" H-pipe would be a good enough location under the assumption that the sensor will read from both banks?

 

[EAC]

I'd like to know too. I have my front header off, so I think I'm just going to have a bung welded on there.

 

[Mac Attack]

Hey Regan, did you place your sensor yet?

If not, my guess would be to place it on the front bank. It should theoretically be warmer there, and for high HP cars the front bank may be fuel-starved due to the fuel feed line configuration (feeding the rear bank first). I plan on redoing the fuel system so it is a simple tee where each bank is fed equally.

Dave

 

[kookoo4nsx]

I can understand if you are monitoring both banks to have the widebands way upstream before the pipes merge. I have a single AEM wideband
after my turbo.

Can the AF ratio change significantly in the 4-5 feet of exhaust between the headers and the tailpipe?

 

[Mac Attack]

I don't think it should. From my limited knowledge, you just want to make sure that it is well before the tailpipe(s) exit so you don't have any interference from outside air screwing up the ratio.

Obviously, this concern is negligible too with smaller diameter tailpipes and increased engine speed.

OEM's want the sensor as close as possible to the heads, just before the pre-cat and just after. The reason is most emissions these days are just at startup when the cats (and sensors) are cold. The sensors are more accurate at a certain hot temperature, and the engine controller wants to know precisely what is going on the first few minutes of startup so it can make adjustments. This is critical to meeting the SULEV or whatever they call it now.

My office neighbor used to work at Bosch in Germany designing these sensors.:smile: He said they would have problems with condensation in the sensors in the first few minutes of startup screwing up the readings and prematurely failing the sensors. Another good reason to warm them up as quickly as possible.

Dave

 

[RYU]

Thanks Dave. I'm using my interim exhaust setup at the moment which comprises of the NA2 headers and a set of HF OBD2 cats. I was able to screw in the Bosch WB sensor after the front bank Cat since there were bungs already there post cat for the OBD2. It just makes my life easy for time being and gets me a very general baseline of my AFR. Unfortunately, I don't recall what i've ready about post Cat measurements... is it going to read leaner or richer? It's also tough to say because who knows how effective these HF cats still are which skews my readings even more. So far I'm hovering around 14.8-10.8 from idle to WOT.

I've decided to just get a full EMS and be done with it. With the driving that I do I don't like the behavior of the RRFPR. A proper tune *should* put me up into 350-370hp hopefully and still allow me to pass the sniffer (with new cats). All I really want is a safe and stout 350hp. Might do a 10-20 shot of Nitrous to address the high IAT problems. Still pondering the meth idea though.

 

[jwmelvin]

I'm adding a Zeitronix wideband to my (brand-new to me) CTSC car that has Comptech headers & exhaust. Currently it has OEM cats, one of which is causing a CEL for degraded performance (P0430).

Would appreciate opinions on the following approach:

(1) replace post-cat O2 sensor with wideband. If desired, feed simulated narrowband from Zeitronix to ECM. This would allow me to check the AFR right now with nearly zero expense, albeit with somewhat reduced accuracy (I understand it will read lean by 0.1-0.2?). I might eliminate my CEL (P0430) with the simulated narrowband signal (which can be shifted lean/rich by the Zeitronix).

Then, the longer-term plan would be to:

(2) replace cats with high-flow cats including pre-cat bungs for wideband. This obviously has the benefit of better flow and eliminating the P0430 code.

Another option is to put bungs in the Comptech headers. But I believe that will require removing the headers for access, and I'd rather not waste the money/labor if I'm going to put in high-flow cats anyway. It looks like I will need to since the P0430 code keeps showing up.

One more question: is there a chance the P0430 code is a result of post-cat O2-sensor performance? It's not throwing a code for the sensor, but it still seems strange to me that the OEM cat is dead after 37k miles (all with CTSC and some recently with a nonworking pre-cat O2 sensor on the same bank as the degraded cat).

Thanks.

 

[M-P]

(1) replace post-cat O2 sensor with wideband. If desired, feed simulated narrowband from Zeitronix to ECM. This would allow me to check the AFR right now with nearly zero expense, albeit with somewhat reduced accuracy (I understand it will read lean by 0.1-0.2?). I might eliminate my CEL (P0430) with the simulated narrowband signal (which can be shifted lean/rich by the Zeitronix).

You need to have the wideband before any catalytic converters to get a proper reading.

 

[jwmelvin]

You need to have the wideband before any catalytic converters to get a proper reading.

Do you know how far the reading is off after the cats? I figure since it would read lean then if I am safe with that reading then I am safe in reality. Are you saying it's a worthless measurement? What about tuners who use a tailpipe sniffer?

 

[M-P]

Do you know how far the reading is off after the cats? I figure since it would read lean then if I am safe with that reading then I am safe in reality. Are you saying it's a worthless measurement? What about tuners who use a tailpipe sniffer?

It just adds and extra variable that is dependent on catalyst efficiency which is dependent on many things like temperature, age, etc. The fact that temperature has an effect means that the relationship between pre and post-catalyst AFR is non-linear.

EDIT: According to Innovate Motorsports..."Measuring after the cat will result in leaner-than-reality readings, depending on the efficiency of the cat."

 

[jwmelvin]

Yes, the leaner-than-reality reading is what I expected. That's why it seems like a reasonable, zero-cost approach to make sure my AFR is safe. I hear what you are saying about the unpredictability that results from influences of temperature, age, etc.

This article is pretty informative, and shows no difference in steady-state measurements but a delay on the order of seconds for the post-cat sensor during transitions.

 

[M-P]

This article is pretty informative, and shows no difference in steady-state measurements but a delay on the order of seconds for the post-cat sensor during transitions.

Interesting article, thanks for the link. Looks like in their tests that roughly 6-8 seconds for the post-O2 sensor to reach correct engine AFR's.

 

[RYU]

for initial investigatory purposes I'd be fine placing the WB post cat. I did for many months in my CTSC Zietronix setup. Once I entered the custom tuning phase I moved them upfront.

I didn't realize the Zietronix has an O2 emulator. Cool.

- - - Updated - - -

btw... I was running HF 300 cell cats which negates the issue somewhat.

 

[k20fg]

I remember reading 18"s down the piping from the head is where you'd want a WBO2.
That measurement could be on the downpipe of turbo builds but regardless you want it pre-cat.

 

[jwmelvin]

Yea I ended up with a bung welded in the Comptech headers before the cat. It's only on one bank but that was about as good as we could do without pulling the headers.