bhancock4 Posted March 30, 2021 Share Posted March 30, 2021 I have a 2005 Honda Civic 1.7l manual transmission with 154,000 miles that does not get driven all that often. 2 years ago had major tune up...plugs, coils, timing belt, water pump, new clutch, etc. About 2 weeks ago I replaced the upstream and downstream O2 sensors with Denso sensors because I had been getting a P0420 emission threshold efficiency code for about the last year. That appeared to resolve the engine codes and has been running fine. Fast-forward to yesterday and I noticed that when revving the engine beyond about 1,700 rpm or so and releasing the throttle it makes a horrible rattling/grinding noise from around the left side of the engine accompanied by a large puff of white smelly smoke from the exhaust...can't tell if the smell is "sweet"...smells bad to me. You can see a video of me reproducing this sound here: Video of noise The coolant was a little bit low (maybe 6-8oz) although I hadn't checked it in a while. I did not see any milky residue under the oil filler cap or on the oil dipstick. I did not visibly observe any bubbling under the radiator cap or the coolant reservoir (although the system wasn't full so maybe I would not have anyway). I am purchasing a block test kit and will be doing that later today but this noise really concerns me. Thanks in advance. Quote Link to comment Share on other sites More sharing options...
bhancock4 Posted March 31, 2021 Author Share Posted March 31, 2021 UPDATE: I did the block test and it was negative. Then used a long screwdriver to feel for vibration and it's definitely coming from the catalytic converter so I'll just swap that out. Was hoping to get by with O2 swap, but I guess that's what I get for driving with that code on 🙂 Quote Link to comment Share on other sites More sharing options...
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