Knock Sensors and O2

[94530inh]

My dad had the bimmer towed to the stealership since it broke down like a mile from there. they diagnosed, and replaced the starter they said the wiring melted. A grand later I told my dad to stop right there and not get anything else fixed there.

The codes they pulled mean bad knock sensors and a bad o2 sensor. how much do these go for and how hard is the knock sensor install. I believe two of the sensors are bad.

Thanks
George

PS its a 1994 530iA With the V8

[winfred]

there are 4 knock sensors and you need to pull the intake to get to them, id do all 4 at the same time and while the intake is out do the pcv plate on the back of the intake and the seal on the throttle body end of the intake, the sensors are around $75 each, sealing up the intake may take care of the 02 codes as intake vacuum leaks are a fairly common v8 problem

[dbals]

there are 4 knock sensors and you need to pull the intake to get to them, id do all 4 at the same time and while the intake is out do the pcv plate on the back of the intake and the seal on the throttle body end of the intake, the sensors are around $75 each, sealing up the intake may take care of the 02 codes as intake vacuum leaks are a fairly common v8 problem

can you help me better understand what a knock sensor does and what are the symptoms of faimlier?
sorry if its a noob question, just trying to make sure I understand.
thx

[winfred]

the knock sensor is basicly a microphone that's tuned to a certain frequency that listens for preignition, when it hears it the computer retards the timing till the ping stops, when one fails the computer retards timing to a safe level and sets a code

[Bill R.]

piezoelectric crystal. Which the Curie brothers discovered a good while back that if you struck quartz and many other crystals a blow with a hammer they would give off a burst of voltage or a spark. If you compress it, strike it ,distort it in any way it gives off this voltage. If you've every used a gas grill with one of those stupid push button igniters, thats a piezoelectric crystal giving off that spark. When knock occurs in the engine block the crystal reacts by giving of a spark or burst of voltage that the dme reads as knock and retards the timing accordingly depending on how frequent the voltage burst occurs, based on this it constantly advances and retards the timing to keep it right on the edge of where knock occurs

the knock sensor is basicly a microphone that's tuned to a certain frequency that listens for preignition, when it hears it the computer retards the timing till the ping stops, when one fails the computer retards timing to a safe level and sets a code

[94530inh]

anyone have a tutorial on how to take the intake off?

[winfred]

thought id keep it simple

piezoelectric crystal. Which the Curie brothers discovered a good while back that if you struck quartz and many other crystals a blow with a hammer they would give off a burst of voltage or a spark. If you compress it, strike it ,distort it in any way it gives off this voltage. If you've every used a gas grill with one of those stupid push button igniters, thats a piezoelectric crystal giving off that spark. When knock occurs in the engine block the crystal reacts by giving of a spark or burst of voltage that the dme reads as knock and retards the timing accordingly depending on how frequent the voltage burst occurs, based on this it constantly advances and retards the timing to keep it right on the edge of where knock occurs