engine light not on but stilll throwing out kncok sensor and CAT codes

[migsk8]

ok so i bought a 97 240sx and the owner told me that the car needed a catalytic converter. so when i get home, check the ecu it throws code 72 and 34, which is knock sensor and the cat. i change out the knock sensor and i clear the codes. when i go to start the car i rev it and it throws out a lil cloud of black smoke like it always does when i accelerate. i go back to the ecu and check the codes and it still reads code 72 and 34..... wtf is up ? also the engine light is not on at the moment but im sure it will come on later today when im driving it, just like it did when i first picked it up.

[Full Street]

dont know if this will help you at all but i think my friend had the same problem. on his Talon he was getting knock from his little computer PDA thing but he wasnt actually hearing his engine knock. he spent a bunch of time searching and searching and he finally figured out it was the stupid $2 Bosch spark plugs he put in. hope that helps.

[migsk8]

that could be it idkm i already changed the plugs and changed out the knock sensor. but what i think it was is the timing was off and there was a lil spark knock. and kncok sensors go out from too much use.......is what i was told

[Full Street]

What type of plugs are you using?

Well just like every other code, its not telling you what is bad, its telling you where the problem may be. The knock sensor code doesnt mean that your knock sensor is bad, it means its detecting knock. It could be phantom knock from exhaust leak or exhaust bumping arround or lifter tick/valvetrain noise. Definately check your timing. Also try throwing in some premium fuel and seeing if it goes away, if so, its not phantom (fake).

The cat code could be a bad rear o2 sensor, or a faulty catalytic converter, it wont just go away by clearing the codes.. Let us know.

Also is it misfiring at all under acceleration??

[migsk8]

What type of plugs are you using?

Well just like every other code, its not telling you what is bad, its telling you where the problem may be. The knock sensor code doesnt mean that your knock sensor is bad, it means its detecting knock. It could be phantom knock from exhaust leak or exhaust bumping arround or lifter tick/valvetrain noise. Definately check your timing. Also try throwing in some premium fuel and seeing if it goes away, if so, its not phantom (fake).

The cat code could be a bad rear o2 sensor, or a faulty catalytic converter, it wont just go away by clearing the codes.. Let us know.

Also is it misfiring at all under acceleration??

i forgot what plugs, but i picked up oem from nissan, i redid my timer and had autozone clear the code and it hasn't come back yet. neither has the cat code. ill let you know if it does come back, i still need to change out the cat tho