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Knock Detection Circuit

The reason for this circuit is simply that standard Fieros do not come with a knock sensor provision. While the TDC/DOHC ECUs DO have a knock provision, the Haltechs do not. If you are running the Haltech, chances are pretty good that you are turbocharging the motor, which means that knock detection becomes even more critical for maximum performance and to lessen the chances for engine failure due to detonation. While this circuit is not active, meaning it will not adjust the timing automatically, it WILL let you know that a timing adjustment must be made.


Here's the schematic


Parts List

Most of these parts can be located at your local Radio Shack or can be ordered via online vendors such as Mouser, Digikey, JameCo, etc...

Don't forget to pick up a breadboard and project box to mount all of the components in. Nice feature is that you can remotely mount the switches and the LED indicator to your dash and hide the project box for that stealth look. Try to keep all leads as short as possible.


C1 .1uF Non Polarized Disc
C2 .01uF Non Polarized Disc
C3 1uF Tantalum


R1 390 Ohm, 1/2 Watt, 5%
R2 100K Ohm, 1/4 Watt, 5%
R3 15K Ohm, 1/4 Watt, 5%


IC1 LM555 or Equivilent


D1 1N914


SW1 Alarm On/Off
SW2 Momentary Activation, Normally Open

Piezo Buzzer

SG1 85 DB 3/4"


Be sure to take your time  when soldering to ensure that you have a good connection without an excessive amount of solder. Also make sure that all connections going to the Knock Sensor are soldered and heat shrink protected for a good connection. The knock sensor should be the standard GM type, but it's always wise to replace it while the motor is out of the vehicle.


Author: 85frankenstein

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