Hey Scotty I have a 2008 Lexus GS350 with 124k miles. Engine has a deep knocking sound almost inaudible but sounds wrong. CEL is on for p0420 and p0430 and person who sold me the car recently replaced the cats and the sensors, also put non foulers. What could be the problem here ? Car seems fine i did most maintenance I could on engine . Mpg are low but that aside everything functions normally.
Cleaned MAF
Replaced air filter, oil, coolant, alternator, idler and tensioner pulleys, throttle body cleaned, PCV replaced, fuel system cleaned, new battery. All parts oem except the cats i already mentioned.
Since you are seeing essentially the same code for each engine bank it is likely something that is affecting both sides of the engine. See the following links for potential causes of P0420/0430 and diagnostic procedures:
https://www.walkerexhaust.com/support/tech-tips/diagnosing-catalytic-converter-p0420-code.html
https://www.carparts.com/blog/p0420-code-catalyst-system-efficiency-below-threshold-bank-1-2-2/
https://www.obd-codes.com/p0420
Usually a deep knocking sound is caused by rod knock due to a connecting rod bearing being worn. The connecting rod connects the piston to the crankshaft.
Are the non foulers installed on the O2 sensors for the cats?
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