Originally Posted by
93MARKIII
first time ive heard this....is it an accurate rule of thumb ? cause my stuff is reddish brown
You can temporarily remove the 02 sensor ahead of the cat to see if power returns, or take a pressure read at the bung hole. Should be less than 3psi. Or take to muffler shop & have checked. Habitual use of higher than 87 octane will poison & clog a Cat. If replacement is required 7 you have two inline, replace w/ a single hi-capacity unit.