I want to test exhaust back pressure.

[hefftone]

I need to test for a clogged Catalytic on My 1997 BMW M3.

I want to use this vacuum/pressure gauge from Harbor Freight.
http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

But I am not sure how to connect it to the exhaust before the catalytic....I could make some BS to attach at the O2 bung, but its a pain to get to.

I keep hearing about drilling a 1/8" hole in the exhaust just before the catalytic, but what it the hell is going to securely fit into a 1/8" hole?

 

[twomanymontes]

I always use the O2 sensor port. I know it's hard to get to, but drilling holes into the exhaust is just asking for trouble