1990 240DL Sedan

Recently, I've heard a noise from under the front of the car that sounded like an exhaust leak. A few years back I had the header pipe re-welded to the flange that connects the header pipe to the catalytic converter; I though this might have separated again.

But before I could check it out, while driving I heard a clunk under the car and saw something roll onto the road; I thought a bolt must have come loose. Now the exhaust leak noise was really loud.

Turns out the weld of the header pipe to the flange for the converter is just fine. What came loose was the test port for the oxygen sensor on the header pipe. There is a nice clean indentation on the header pipe, and the bolt/port that I retrieved off the road fits perfectly.

I do not believe this test port was ever used by my mechanic. Is there a way I can plug this hole to avoid replacing the entire header pipe, and probably the catalytic converter?

I realize this would be a temporary fix, but after 3-4 years the weld of the header pipe to the flange has held up. Why not a temporary fix here until the header pipe and the converter really need to be replaced.

Would welding some metal across this hole make sense, or something else?

thanks

 

just cover it then. We got rid of it when when did the new exhaust.

 

So...you found the O2 bung nut, right? Will it not screw back in? If it will, screw it back in. If you're worried about it coming loose, have some one tack weld it to the pipe. If the threads are no bueno I'd just run it in as far as I could and tack it. Hard to believe it came loose; those suckers are usually rusted tight!

 

RE: So...you found the O2 bung nut, right? Will it not screw back in?

Bung is a new term by me.

Bentley (241-28) shows the header pipe coming into the catalytic converter. My O2 sensor is mounted on the catalytic converter, not the header pipe as in Figure 26. It is okay.

What fell off is the test port plug in Figure 26, including I guess what would be referred to as the bung (hole) that the plug was screwed into. This bung looks like it was welded to the header pipe; I can see a slight indentation around the circumference of the hole in the header pipe.

Certainly no way this plug is going back in the hole. So I will just get the hole welded with a metal patch and be done with it until the header pipe needs replacement.

Thanks all.

 

Yeah, basically a bung is any bolt that's primary purpose is to fill a hole but allow periodic access. The hole has thus been referred to as the bung hole. The most prevalent usage is on a 55 gallon drum...the holes that have big plugs for access to the content.