G50: Question About Knock Sensor Emulator

[sdkhalsa]

In a past listing by Q45tech, he made mention of a knock sensor emulator. Anybody have the details? I have heard that some people have used a 1 M Ohm resistor to ground the positive lead into the sensors with varying degrees of success. Anyone know the desired voltage reading on the ECU side of the knock sensor leads?

[Q45tech]

The KS microphone is ~~ 550,000 ohms resistance, the audio is coupled to ecu with a capacitor to block the dc test/polarization voltage supplied by ecu.

Failure to properly pull down this polarization voltage [by the 550k resistance] will show up as an open KS.

The KS circuitry in ecu expects some noise to be picked up by KS so lack of noise or lack of pull down voltage will show a code.

Just subsituting a 550k resistor for KS will leave KS circuity without the noise and it will eventually decide to reduce ignition advance and not throw a code.

I leave it up to members to THINK how one could decouple the KS resistance and yet pass the noise to ecu from existing KS.

One might start with calculating the capacitive reactance of a capacitor at 1k* so that this frequency is not reduced by more than 6 db

0.3 uf at 25v would have 530 ohms..................1/1000 of the 0.03 uf............................ 53000.003 uf .........................53000

* important to learn what knock frequency actually is!http://home.netcom.com/~bsunda...s.htmh ... d/...k.pdf

http://www.kusashi.com/reactance-c.php

The ecu KS circuitry opens a 12-35 degree WINDOW [alternates bank to bank after IGNITION for each cylinder and tallies each bank for SEPARATE ignition reduction], just as each bank is trimmed for fuel injection by O2.

Bad knock usually occuts at or near [+-] TDC. Wheras peak power occurs at 14-16 degrees after TDC!

The emulator is a test tool used for a specific test [to sell new KS*] not to substitute full time for a bad KS.

* TO SHOW/PROVE to customer what spending the $900 will accomplish.

The KS harness also contains the coolant temp sensor wiring.

[Q45tech]

Based on the Q engine bore you will find the knock frequency to be ~~ 6KHz.

"A chart from the SAE paper shows that the fundamental frequency of a 75mm bore is about 7kHz, a 94mm bore is about 6.0 kHz, while that of a 110mm bore is about 5.2kHz. The chart shows a fairly linear relationship of frequency to bore diameter."

http://www.streetrodstuff.com/...x.php

[sdkhalsa]

Thank you so much Q45tech, that was quite some answer. It occurred to me that one could find a used Q knock sensors, bolt it to a suitable location on the engine and jumper it into the circuit. Anyone think of a simple way to generate noise off an elementary resistor circuit?

[Q45tech]

A capacitor passes high frequencies and blocks DC. The ecu has a capacitor to block the dc polorizing/test voltage.................

ECU-----//Cap--X* ECU connector-----Harness-------KS

ECU---------------^

Ecu has 2 circuits one to listen and one to read the voltage drop cause by the 550k resistance of KS measure at X prior to capacitor