Wideband o2 sensor location

[Johner]

I'll be mounting an AEM wideband sensor to my car this week. I have SSIs and a non-stainless Dansk Sport 2 in 1 out on my car, and rather than install on the SSIs, I was thinking about mounting on the muffler. This is based on reading this post: Wide Band O2 sensors, must know info! and should also make the install a bit easier (won't have to remove the heat exchangers, don't need to find someone to weld stainless)

I found this image of a Dansk sport and have marked aprroximate locations where I think I can fit a sensor. Both would allow me to fit the sensor so it is angled down



Can anyone comment on whether these locations are reasonable?

Thanks

John

[PeteKz]

I am installing a bung into my SSI's right now. I chose the large pipe just after the 3-pipe collector because that will be hot enough for the lambda sensor to operate correctly. That's also where most other people have installed them.

The sensor must be HOT, which is why later model cars use a 3 or 4 wire sensor--those extra wires provide power to a heating element in the sensor to help it warm up to operating temperature faster, and maintain it during fuel shutoff on overrun and coasting. Several online sources quote the minimum operating temperature for a lambda sensor as 350C/662F (although I couldn't find the minimum operating temp on Bosch's site, only maximum). That's a lot hotter than I think the outer chambers of the muffler will see, otherwise I think you would scorch the paint on the rear valence of your car.

https://autoditex.com/page/lambda-sensor-o2-sensor-21-1.html

From what I've read, the pressure correction for the sensor reading only applies to turbocharged engines, between the exhaust ports and the turbocharger, where the pressures will be higher than downstream of the turbo. In the example Sal provided in the link, it takes 7psi to require a correction from .088 to .091, less than a 4% correction. I don't think a low restriction exhaust will cause anywhere near that pressure from the collector back.

So I am skeptical of installing the sensor in the muffler. If that's what I were considering, I would wait for someone here who has done it and can verify that it works correctly, or put a temp probe into the muffler at that point and measure. FWIW, I've never seen an OE installation of a sensor into the muffler, only further upstream at, and before, the cats. If I really wanted to install the sensor in the muffler, I would install as close to the exhaust inlet to the muffler as practical, in order to help keep it hot.

[icarp]

Pete has it right.
The best place for the o2 bung is 3-6" past the collector , 3 into one .
The bung can be welded in while the SSI's are mounted to the car . The angle of the sensor
needs to be 15 degrees or more, off of horizontal , that is so any condensation will not collect in the sensor . The angle # is not critical, just enough to drain it . Also think about the sensor not interfering with the exhaust valve cover . The best welding method is TIG welding. $ 100-125 should cover it . Bring the right drill bit and your bung with you.

Mounting in the muffler will give you an AFR number that is right , just slower to respond and might be too low in temp to burn off the condensation. This will also take longer to reach Operating temp and be harder on the sensor . Thus requiring a more frequent change of the sensor.

Ian

If you will tell us where you live, in your signature , we might be able to recommend a shop

[brighton911]

What icarp said. A muffler location will cause you all kind of negative issues, do the right thing and have a bung welded in.

[jpnovak]

If you want to install in the muffler you can weld the bung in the elbow. Between the mounting flange and the muffler body. Just make sure that you do not have any gasket leaks that will allow false air to enter.

This is one way to install a muffler and get the same reading as the heat exchanger. This location is about 10" behind the collector on SSIs.

[FA-18C]

Just did this on a premuffler, added a WBO2 bung just aft of the O2 sensor location to have both. TIG welded, installation this week. Will get to the WBO2 wiring install once I get car back from clutch install.

CATs get HOT. After a 30 minute drive with lower valve covers at ~210, CAT was in the 450 range.

[PeteKz]

Man, you guys with TIG welders! I gotta get me one of them things one of these days. I'll just make a mess with my olde MIG.

JPNovak has a good suggestion with putting it in the elbow to the muffler, rather than in the muff can--if you know you will keep that muff. I tend to experiment with exhausts, and the muff is the easiest thing to change, so I would need to weld in new bungs when I change it. Whereas, I will keep the SSI's long term (forever?).

[Johner]

Thanks for the replies. I will take the car to a local shop that does stainless exhaust work, and see if they are ok with welding without removing the heat exchanger. Otherwise the backup of the muffler elbow looks good, although a bit tight for space.

John

[PeteKz]

Just put it on the collector pipe of the SSI. It's easy enough to get at, and be sure to tilt it up. I prefer to tilt it higher, say 45 degrees, so that it's out of the way of road spray, mud, sticks, and other crap kicked up under the car.