Bung on top of crossover pipe Y

[Ed81DMC]

I’m replacing my left exhaust manifold gasket. Anybody know what this “bung with a bolt in it” is for?
See photo.
Also what is the bedt tool to loosen the upper left (driver side) of the 4 nuts attaching the crossover pipe to the exhaust manifold? It squarely blocked by the oxygen sensor! I’m thinking of using a 17mm crow foot because a 17mm socket won’t fit over the nut without removing the oxygen sensor - which I can’t remove.

What is the best tool to remove the oxygen sensor (if I have to remove it)? It points toward the side of the vehicle and a longer sensor socket won’t fit over the sensor. Is it 13/16” or 20mm or 21mm?

[Ed81DMC]

I’m replacing my left exhaust manifold gasket. Anybody know what this “bung with a bolt in it” is for?
See photo.
Also what is the bedt tool to loosen the upper left (driver side) of the 4 nuts attaching the crossover pipe to the exhaust manifold? It squarely blocked by the oxygen sensor! I’m thinking of using a 17mm crow foot because a 17mm socket won’t fit over the nut without removing the oxygen sensor - which I can’t remove.

What is the best tool to remove the oxygen sensor (if I have to remove it)? It points toward the side of the vehicle and a longer sensor socket won’t fit over the sensor. Is it 13/16” or 20mm or 21mm?

Photo of the bung on top of the crossover Y pipe Attached

[mark w]

its removable so that you can insert a pipe and using a gas analyzer tool you can read the AFR or CO (mixture).

there is one on each side so that you can read each bank.

[mluder]

I found the top bolt on the driver's side was easiest to get at with a combination wrench from above. Even then it wasn't easy.

Cheers
Steven

[DMCMW Dave]

Oxygen Sensor is 13/16". Best tool to remove it is an oxygen sensor socket and/or an open end wrench, right after heating the bung with an acetylene torch.

[dn010]

If you don't have an acetylene torch or even a turbo torch, run the engine to get things hot and then try to remove the sensor. Obvious warnings - wear gloves, don't touch the hot pipes, etc.