How to install wideband O2 sensor bung
 

I was looking for a place to put a wideband O2 bung in the downpipe from the turbo, which would not block access to the nuts holding the catalytic converter pipe assembly to the downpipe, allow the O2 sensor to be removed without a hassle, and also be protected from the road and junk that may be on the road. This can be done with the car on jack stands, without removal of the downpipe.

Overall, I consider it to be about a 2 on a difficulty scale of 1-10, but you need some specialized tools to complete the job. IE, a minimum of a 130 amp MIG welder, stainless welding wire spool, Argon gas bottle, assorted drill sizes with a 3/4" diameter drill bit (minimum) for final install, and a drill which can take the final drill bit size. I may be bidding low on the difficulty scale. An air filter install is a 1. Building a certifiable 25.1C/D NHRA chassis would be a 10, given that is the most difficult fab job I've ever done, and I never want to do it again.

The best compromise of locations that I found, was on the passenger side of the turbo downpipe, just above the sheet metal cover plate which is installed to protect the fluid lines in that area. This location allows access to the cat converter nuts, is protected by the cover plate, and once completed the O2 sensor can easily be installed and removed without removing the cover plate. There is also plenty of room to access the O2 sensor hex with a wrench.

First you will have to remove the lower heat shield mounted on the bottom side of the downpipe. You will not have to remove the top heat shield. I actually removed the bottom shield, left the top shield in position, and re-installed the nuts and clamp that hold the shields to the downpipe.

Second, assemble the O2 sensor into the bung and position them between the down pipe and the sheet metal cover plate so there is enough room to unscrew the O2 sensor once the bung is welded in. There are lots of places this can happen in this general area, but you should take into account how much room you need to get a MIG / TIG torch in position to weld around the bung. I did not remove the downpipe from the car while installing.

Once you find a good location, draw a circle around the bung with a marker. Pull the bung / sensor out and estimate the center of that drawn circle, and mark a dot at that location. Once you estimate the center, remove the cover plate from the bottom of the car. It requires a 12mm and 14mm socket.

After removal, use a punch and hammer to create a dimple at the center of the hole you marked. Once the punch was marked, I drilled a 1/8" pilot hole at that location. I then drilled a 3/8" hole, and then a 3/4" hole. Once the holes were drilled I cleaned the burrs off with a speed de-burrer.

Now you can test fit and tack weld the bung. Thread the O2 sensor into the bung and position the bung so that the sensor goes into the hole. While doing this, it is good practice to not actually use the expensive wideband O2 sensor unit during test fitting and welding. In the pictures, I'm using a worn out sensor I had kicking around. With the old sensor installed in the bung, and the bung pressed into position against the downpipe, tack weld the bung in a couple places. Remove the O2 sensor and check around the bung for excessive gaps. If you have to tap the bung around a bit to close up a gap, make sure to reinstall the sensor to ensure it still goes through the drilled hole. Also, if you wanted, you can install the O2 plug to make sure it goes through the drilled hole as well. I didn't actually do this, since I use an old O2 sensor as the plug when I'm not running the wideband.

Once the tack welding is done, re-install the cover plate and make sure there is enough room to get the O2 sensor in and out prior to final welding. If there is enough room, then remove the cover plate again and weld away.

Once the bung is welded around the perimeter, use a small flashlight and check around the welds to ensure there are no gaps that were missed. My weld is kind of ugly, because I was unsure of a couple spots. Lying under the car on my back and welding in an odd position made me not complete a clean weld in a couple spots. I welded them a second time just to make sure there were no leaks.

After the bung is welded in, thread in the old O2 sensor, and start the car. You can spray a little soap and water mixture onto the tubing around the weld and see if it bubbles. However, the hot exhaust will evaporate the water off real fast, so look quickly.

Once you are satisfied with the weld job, you can tighten the bolts holding the upper heat shield on, and re-install the cover plate. Install the wideband sensor and fasten the wiring with zip ties however you prefer to run it.

Optional:
If you want to re-install the lower heat shield, you will need to mark it and cut a hole so the O2 sensor will go through it once it's installed. I just left mine off and will re-install it over top of the bung if I ever need to remove the sensor for some reason.

more pics

Nice writeup.

The only problem that I see is the location of the wideband sensor. Being that it is close to the 6 o'clock position, it will more prone to moisture buildup. This will eventually kill your wideband sensor. A better positin would be to the sides or top of the downpipe for the wideband.

Agreed. ^^^

At least the 3 or 9 o'clock position --- anything South of there, and the above will prove true.

He is correct.
Don't use notice when you start your car in the morning...there is a water coming out from the muffler!

I agree as well, and it even gives the same info in Innovate's instructions, but this is the most practical place to install if you won't want to drop the exhaust, which I did not.

Also, I do not plan on running it full time. I will use and remove. Once I have a different exhaust in I will relocate it.

edit-
Also, when I was reading the instructions on the LM1, it said for permenant installation, to minimize the damage due to moisture, one should start the vehicle prior powering up the sensor. I ran this system in two cars prior to this one since I purchased it in 2003, and have not yet had a problem following Innovate's directions. The directions are as follows regarding permenant installation:

Copied from Innovate's pdf manual:
"It is NOT a good idea to connect the LM-1 permanently to 12V and switch it on before the vehicle is started. The sensor would heat up to its operating temperature. Depending on the climate and the senor position in the exhaust, condensation water can form in the exhaust pipes. This condensation water could then be blown by the exhaust stream against the hot sensor when the car is started. The resulting heat shock can permanently damage the sensor."

What I normally do is start the car, let it run for a few seconds to blow out the moisture, and then turn on the wideband. I should have posted this stuff last night, sorry, I guess I was tired. I undrstand there is a life to the snesor and the way it's installed will shorten it. I guess that's just the cost of doing business, as the saying goes (although I'm not actually a business).

Another thing I forgot previously.

The sensor in the pics is actually not at 6 o'clock, but really more like 4 o'clock to maybe 4:30.

When preparing to drill the down pipe, it's very easy to press the convert and down pipe assembly over by hand, sso it is at full stop towards the driver's side of the car. This allows more room for the drill. Once the bung is installed I swung the down pipe back into it's center position. This placed the sensor just past 4. It's not 3 o'clock, but it's definately less than 5.

Pics of the sensor wire routing.

any issues with welding a steel bung onto stainless steel exhaust?

Nope. It's pretty easy to weld steel to stainless. I MIG'ed it on with a spool of .035" stainless wire and C25 gas. You could use regular copper coated steel wire and it would work fine as well. The bung will rust, and probably the weld bead, but I'll have been dead for 100 years before it rusts all the way through and the bung falls out. :)

heh, I take it there aren't any stainless bungs available? I'll be doing this next week once my new MIG comes in, my brother toasted the old one:-/

Too much worry about little things. If you are worried about the bung rusting, just shoot it with some several coats of BBQ paint or Hi-temp paint. As long as the metal itself is not exposed, you should be just fine.

I've seen stainless bungs on ebay. Just make sure they are M18 x 1.5 thread. Although I've never actually heard of an O2 bung that wasn't M18 x 1.5 thread, but maybe it exists. Probably in a British car...

cool, just grabbed them on ebay...you can get a pair for $6 + ship.

wait, I can get a BUNG, no a PAIR of BUNGS for $6 shipped?
su-wheat!
Wait....sorry. I was thinking of something else. :lol: