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Effects of spark plug heat range?

240 Views 0 Replies 1 Participant Last post by  Innate
This question arose with my wife's CR-V recently, but the answer will also be needed for my '96 S-10 at it's next inspection.

A code keeps getting thrown, P0420, B1 CAT deterioration, below efficiency threshold, apparently the CAT is not firing off as it should. The engine is known to be good, 165K miles, runs a little rich by the tailpipe color, but mpg, performance good, no other codes ever. The CATs were new 60 K ago, NAPA - likely Walker mfg. I have to get it through inspection again. In the past, per our now-retired mechanic, we ran the tank down and topped with High Test, cleared the code, ran it 100 miles, the code hadn't returned, we got the sticker. This time I'm anticipating doing the same, but need to change plugs, which I'll do first. I can go up or down in spark plug heat range, and wonder if this is the time. If the rear CAT is not firing up as it should, will changing heat range help? What direction, I personally can theorize why either direction might help? And how does the O2 sensor play into that, would new ones make this better, or help? The engine was an identical match good motor swapped into her now 302K car 60K ago, exhaust is original and perfect, with those new CATs.

Someone out there in forum-land must have been down this road. Thanks!
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