Knock Detection discussion

[clint78z]

There appears to be some confusion on knock detection on engines.

 

First I will start with the components. A "Knock sensor" is a piezoelectric microphone screwed into the side of the block. This mic takes ALL NOISES from the engine and transfers it to a varing voltage pattern that looks exactly the same as the noise frequency. Now some of this noise or frequency is normal from engine mechanicals. This varing voltage from the knock sensor goes to a Filter which is in a module or built into the ECU. The filter is responsible for detecting if the voltage pattern is knock or normal engine noise. If it is knock the ecu pulls timing out.

 

This works well on an original ECU and Knock system. If I try and use a knock filter from a chev 350 on my L6 it will not detect it properly, either false alarm or not detect it. If I put a TEC II and a knock sensor, I am left guessing what noise is knock and what isn't.

 

My main point is unless you have a knock sensor and filter design for that specific engine it is a bit of a poke in the dark. Do not fully rely on these sensors to keep you turbo engine from exploding. TUNE WISELY

[SleeperZ]

I agree Clint, as a general rule the knock sensor and ECU need to stay with the factory engine to function properly. I've been unsuccessful so far getting the 280ZXT knock sensor to work with my Z31 ECCS and L28ET engine - I get an ECU error code for the sensor immediately. I suspect the L28ET, with solid pivots, is a bit noisier than the VG30ET motor.

 

If I get my engine tuned properly with a wideband O2 sensor (plan on building my own DIY), I will reconnect the knock sensor and wire an attenuator in between the sensor and the ECU, and progressively and proportionally reduce the signal until I no longer get the error code. At this point, I may have a functional detonation sensing system...maybe.