o2-bung

Oxygen sensor bung installation

Links to other articles in this series.

AFR introduction

O2 controller

Throttle body modification

DIY ECU kit

Modifying the Megasquirt

First things first:

Since my present ECU doesn't use an oxygen (o2) sensor, the first thing I had to do was weld a bung onto the exhaust pipe to be able to install an o2 sensor.

Note:

Bosch has a "Technical Customer Information" .pdf file that gives the complete specifications of the LSU 4.2 wide band oxygen sensor. Try this link to get the .pdf, http://www.ontronic.com/products/doc/Bosch_LSU_4_2.pdf

This link, Y 258 K01 005 000e should also get you to the document.

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".

This is the bung and plug I bought on eBay for $6 delivered. If you decide to use this type bung, don't fall for the $20 version of the exact same thing without the plug.

Notice the curved surface that will contact the exhaust pipe. This allows a nice fit onto the exhaust pipe with minimum gap for welding. But also notice that it doesn't have a smaller reference diameter to center it in the hole in the exhaust pipe. My bung had a light nickel plating on it which needed to be ground off where the weld fillet would be.

As per the Bosch technical data sheet, the bung and sensor should be within 15° of vertical when mounted. This is to prevent water drops etc in the exhaust from getting into the hot sensor when starting the car on cold days. The sensor element heats up very quickly and could be over 700° C before the engine even starts.

Mounting the bung:

To use this bung, center punch the exhaust pipe where the center of the bung will be located and drill a small pilot hole first. Then work your way up to the final hole size of 3/4" in diameter.

Carefully center the bung over the hole and clamp it in position to do your first two tack welds. Remove the clamp, loosely install the plug and continue welding the bung in place. Installing the plug will prevent any splatter from messing up the threads in the bung.

This is where I placed my bung. My best guesstimate was to place the bung 23" from the center of the header flange on the engine.

You have to take into account how much heat the exhaust gases will have so you don't overheat the sensor. If the gases are too cool the o2 controller will use battery power to maintain the correct temperature.

And here is the bung welded in place. Yes, it is -very- loud with the sensor removed!

While it doesn't look like it in this view the sensor is vertical when viewed from the front or rear.

The burned look on the sensor is perfectly normal and is the result of the manufacturing process.