After installation I needed to develop an ignition map to suit my car - but this proved to be very difficult as I couldnt hear if the engine was suffering from pre-ignition (also known as knocking or pinking) due to wind and exhaust noise.Because of this I needed some form of computer to identify when it was happening.
As there was no off-the-shelf solution available, and I wasnt prepared to spend a large amount of time trying to design and make one, I decided to make use of a freely available frequency-sensitive device - the human ear - connected to a very effective detector of unusual noises - the human brain. This solution isnt new and has been used in some form or other for many years, as discussed on Piston Heads. Its a small thing that either screws into a hole in the block, or is held on a stud. Its an piezo-electrical microphone in a very durable package, specially designed to give a strong signal at between 5KHz and 15KHz (5,000 - 15,000 cyclessec). ![]() The headphones should be fairly closed-in, so that external noise is reduced - close-fitting earplugs would also work. I am using a fairly elderly pair of Peltor noise-limiting amplified ear protectors that were designed for use on firing ranges. I used twin and screen cable sold for use with automotive sensors, which comes with heavy and tough insulation. Fortunately the Ford Crossflow block has an unused threaded hole just below the thermostat. I found that it was necessary to wire in a 1:1 ratio microphone transformer between the sensor and the microphone. If youre technically minded, it was necessary because the sensor is what is known as a balanced feed (the microphone itself is not connected to earth, which is only used for the screen) and the amplifier input which is unbalanced live and earth. Direct connection without the transformer resulted in a load of hum and little signal (see the following wiring diagram from Shure). ![]() The following test procedures should only be done on quiet private roads. Knock Sensor Microphone Software Up AndWith the MegaJolt Configurator software up and running, the car was driven at various speeds and loads (e.g. Once the correct ignition map cell was identified the value was adjusted and the test repeated. You can hear the racket made by the engine, but the knock is the harsh rasp that can be heard at the end of the recording.
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