Does anybody know what was in the perfectly round hole in the exhaust pipe of my 1992 Volvo 240 Wagon? Whatever was there is now gone. The hole is about 1 foot upstream of the catalytic converter on the right (passenger side). The hole measures a little larger than 3/4 inch or a little larger than 19mm, so it is a little larger than a threaded 02 sensor hole would be. I cannot find any wires that would have attached to an O2 sensor or a tube or any place an EGR pipe might have led to. (There is an o2 sensor in the front part of the catalytic converter that is intact and I believe the upstream and only o2 converter listed for this model. Hopefully it is just some kind of plug that needs to be replaced but the parts stores have not been able to identify. Any help is appreciated.
Thanks.

 

yeah, only one O2 sensor on this generation of cars.

I believe there's a plug there for sniffing the exhaust pre-cat for certain sorts of engine diagnostics.

 

Do you have one on your 92? Does it look like it threads in or pressed in or? Parts store sold me a threaded 18mm plug which is too small.

THanks for your reply.

 

my 92 is a 740 turbo... Volvo parts catalog says that plug for a 1992 240 is part 948404,

Volvo Exhaust system B230F

part #2 here,