Today in my engine class, my professor mentioned that knock sensors are several hundered dollars, and only available on high end engines even today. Because they are pressure transducers, that makes them expensive.

I was under the impression that knock sensors are fairly cheap and common on today'* engines. Our engines have them.

Any thoughts? Is my prof full of hot air?

GMPD has them for $44 for 92'*.

he doesnt know what he is talking about

I would ask him after class. Not nice to embaress a Teacher in front of the whole class

Do it infront of class.

My first management class was MIS, and the teacher was telling us how most computers have up to 256 mb of ram....

I didn't say anything, but taking tests written for technology a few years ago was bad.

Anyone know what specific kind of sensors these are?

umm...knock?

http://www.stcloudchampionauto.com/pdf/53_KnockSn.pdf


this should help you out

Oh a wise guy, ehh? j/k

Are they an accelerometer, pressure sensor, what?

I'm going out on a limb, but I think the Knock Sensors are Accelerometers. Now I'm curious to find out for sure. Need Gearheads over here.

I dont know the electrical components they are made of but belive they are Piezo electric preasure transducers? Anyway here is an explantaion of operation.

Knock Sensor (KS) System Description
Purpose
Varying octane levels in today'* gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of 2 or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a Knock Sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.

Operation
The PCM contains integrated knock sensor (KS) diagnostic circuitry. Input signals from the knock sensors are used to detect engine detonation, allowing the PCM to retard ignition control (IC) spark timing based on the amplitude and frequency of the KS signal being received.

The knock sensor(*) detect abnormal vibration (spark knocking) in the engine. The knock sensor(*) are mounted in the engine block near the cylinders. The knock sensor(*) produce an AC signal voltage under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensor'* signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltage varying over 0.5 volt more than and less than the calculated average voltage.

Diagnosis
If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.