Honda said i had 2 codes showing up on my 2003 Honda CRV . Has 127000 miles onit and had an after market conv converter installed 2 yrs ago , 108900 mi. One code was for P0420 and the other i don't have access to but they said it was for a knock censor that hinders acceleration. I had the knock sensor installed and the code for the converter has not shown up again and the car has much better acceleration. Could that knock sensor have caused the catalytic converter code to appear?
Well yes it could because if the ignition is too retarded by the knock sensor it can make the catalytic converter have to work too hard because the engine would be running way too lean
THANK YOU, I feel beter about not having to worry about replacing it again!
Yes.
What the knock (=detonation) sensor does, it makes your ECU send the spark through your air-and-fuel mixture earlier, than it normally would.
This is done to avoid "knocks" - to avoid a situation, when the air-and-fuel mixture explodes /detonates by itself, before it got a chance to be ignited by the spark.
So if this sensor notices that a detonation occured, it informs the ECU, and it moves the idnition moment to "earlier", in order to forcefully ignite the mixture before it detonates by itself, in order to avoid engine damage which would have occurred due to a continuous series of such uncontrolled detonations.
However, with such earlier ignition, the whole combustion process in the engine occurs in a non-optimal way, with a ton of negative consequences: excessive fuel consumption, engine power loss, possibly overheating, etc., one of these consequences being excessive quantities of not-fully-combusted materials reaching the catalytic converter. The latter is not designed to and cannot cope with them all, hence parts of those materials reach the downstream O2 sensor, triggering the cat malfunction code, cause the ECU cannot tell for sure what the reason for excessive amounts of non-combusted materials in the exhaust gas flow was: it could have been the too early ignition, but theoretically it could have been a bad cat converter itself. So to be on the safe side the ECU triggers the "bad cat converter" code.
According to your description, in your case the reason for the ECU switching into "detonation-preventative" mode were not real detonations, but just a bad detonation sensor (lucky you). Of course, with this sensor replaced, the too early ignition stopped, and the air-and-fuel mixture got to normal - now the cat converter no more receives excessive quantities of non-combusted materials, and the downstream O2 sensor no more complains about the cat converter´s inability to properly cope with all those materials. And if the downstream O2 sensor does not detect excessive amounts of non-combusted materials - there is no more reason for it to alarm the ECU about the cat converter possibly not doing its job correctly.
Sorry for the long description. Hope I managed to explain how it works.
Thanks for the in depth explanation and its good to know I still have a very good old car!
It's the opposite. When knock is detected, the ignition timing is retarded, ie the spark comes later. Just like Scotty said.
With all due respect, Sir: think yourself: if at some point of time your air-and-fuel mixture detonates with a "knock" even before the spark came - what use is it for you to send your spark even later? At this even later moment, there will be no air-and-fuel mixture in your chamber left for the spark to ignite - just fumes from the detonation.
While the whole idea of moving the spark moment was to prevent detonation. You can only prevent smth if you do smth earlier, than the event you are trying to prevent actually happened.