How to Install a Weld in O2 Sensor Exhaust Bung

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Hello everyone, in this particular video I will be doing a demonstration on how to install a weld in exhaust bung which is typically used for an O2 sensor or also known as an oxygen sensor, but can have other uses as well. In this tutorial I will be also going over the best location for an O2 sensor and what can happen if it's not in the correct position.

Tools/Supplies Needed:

  • drill
  • drill bits
  • center punch
  • hammer
  • carbide grinding bit
  • mig welder
  • wire brush
  • grinder
  • abrasive pads
  • wrench

Step 1:

These exhaust bungs can usually be purchased for a couple dollars at your local auto parts store, this one was purchased from a local exhaust manufacturer wholesaler, along with the rest of the parts as well. I’m redoing the whole exhaust system on this truck which is a 98 Ford Ranger. This truck is equipped with 2 oxygen sensors, therefore it has post and pre cat sensors. The pre is installed on the exhaust manifold and the post is located after the cat which I’ll be installing here.

Step 2:

This pipe will be attached to the catalytic converter and there is usually a specific distance where that o2 sensor should be located. For this I am matching the factory distance which was about 6”. I am also taking the expanded portion of the pipe into account which is why you’re seeing me mark the distance at 7.5”. This will also depend on what type of o2 sensor is used. Some are heated, therefore they can be further away. Non-heated sensors require heat from the engine or catalytic converter to function correctly. Keep in mind, when a sensor is too close, it can also overheated therefore creating a premature failure on that sensor.

Considering this is a pipe, there is a greater risk for the drill to wander, so use a center punch to mark the hold. I will be using a step drill which will easily drill the exhaust pipe and is easily available in larger diameters.

But in order to start out that hole, a center drill should be used. A center drill will create a starting point for the hole and does not flex compared to a smaller diameter drill bit.

Cutting oil can be used to drill the hole. But this is mild steel so it’s not a must. It should also be mentioned that the sensor should be installed anywhere from a horizontal position to the top of the pipe. Meaning between the 9 and 3 o’clock positions. This ensures the sensor will not be effected by moisture sitting at the bottom of the exhaust pipe which may jeopardize it’s life expectancy. You’ll see this a little better once it’s installed on the truck.

Once that hold has been drilled, unfortunately it’s still not large enough for this particular bung as it’s intended to have that lip fit within the pipe. Therefore in order to make it larger, I’ll just use a carbide grinding bit which can be used on a drill or die grinder. Increase the diameter of the hole until it’s the correct size.

In order to keep that hole symmetrical, I used a rubber o-ring closely matching the bung’s diameter with a marker.

Step 3:

Considering the bung is flat and is being installed on an arched surface, this can be a little trick to weld. So short welded will be done while rotating that pipe.

This is aluminized exhaust pipe, it has a coating which needs to be removed before welding. I’m just using an abrasive pad on the angle grinder. If you are working with older exhaust piping which maybe rusted, that rust must be removed in order to get a proper weld.

Also clean up the bung to remove any factory coatings.

Step 4:

Wearing the correct safety equipment for welding, I’m using a piece of wood to hold the bung in place, tack weld so it’s somewhat secure and then we can lay a full bead.

For this I am using a flux-core welded, therefore there is no gas shielding and slag will be present. Remove the slag using a wire brush, this must be done before applying more welds as slag can cause inclusions. I am also applying an anti-splatter spray which keeps the welding process a little cleaner and most importantly prevents any splatter from sticking to the threads inside the bung which can cause issues.

Step 5:

Now apply beads and change your position as needed. From what I’ve found, when welding exhaust pipe 0.030” seems to give the best results and from what I’ve found that is the smallest diameter available in a flux-core application.

Clean up the weld again with a wire brush.

Apply more anti-splatter spray to the threads. Too much spray over the area you area welding directly can cause defects in the beads.

While some portions of the bung are flush on the arch, the sides however is not so this can be tough getting a perfectly smooth finish unless you run multiple beads.

Insect the area closely so there isn’t a chance for leaks and as you can see the sensor fits perfectly without any binding from the splatter. Any splatter can bind in the threads causing damage to the bung or sensor.

Exhaust bung designs can vary and you can also use a large nut of the correct side if you wish.

The aluminized coating had been removed from this section of pipe, it no longer has a rust preventative coating. So as a from of protection the area will be scuffed up with sandpaper.

Then wiped down with a wax and grease remover.

And finally have a high heat paint applied as a form of protection.

Step 6:

Now for installation of the vehicle, as mentioned before this sensor is after the catalytic converter. The sensor must be installed between the 9 and 3 o’clock position as it avoids the chance of moisture damage, along with any interference from being damaged when driving. Ideally, if possible meaning there is no interference with the floor or any other components on the vehicle, it’s best to have the sensor in the 12 o’clock position.

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