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thom4782 · 11-11-2018, 06:12 PM

Cats can go bad.

I don't recall the exact procedure but I believe you can check their performance by using the Durametric to look at the before and after O2 sensors and can compare their profiles.

If I recall correctly, the rear profile should look essentially flat compared to the front's wavy line. If the rear looks like the front sensor's profile, then the Cat isn't doing its job. Of course this assumes, the O2 sensors are working correctly.

Others can confirm is my recollection is close or not. Hope this helps.

11-11-2018, 06:12 PM	#2
thom4782 Registered User Join Date: Sep 2010 Location: Foster City CA Posts: 1,099	Cats can go bad. I don't recall the exact procedure but I believe you can check their performance by using the Durametric to look at the before and after O2 sensors and can compare their profiles. If I recall correctly, the rear profile should look essentially flat compared to the front's wavy line. If the rear looks like the front sensor's profile, then the Cat isn't doing its job. Of course this assumes, the O2 sensors are working correctly. Others can confirm is my recollection is close or not. Hope this helps. __________________ '87 951 '01S 986 (Sold after 16 years ownership) '78 924 (carburated; sold when moving to CA)