PARTS
(1) 74LS74 chip.
(1) 100nf capacitor
(2) 1nf capacitor
(?) Wire
The half circlenotch in chip indicates Pin 1 (polarity) position. With the NOTCH facing UP, pin 1 is the top left. Pin numbers are counted counter-clockwise going down the left side, up the right side to the last pin.
+5v source from the ECU goes to pins 1, 4, and 14.
Put a 100nf capacitor across the +5 power and ground (noise reduction path).
Pin 7 gets grounded.
The signal from the speed wire sensor goes to pin 3.
Pin 6 is connected (bridged) to pin 2.
Output wire back to ECM is from pin 5.
A 1nf capacitor goes from pin 2 to ground, and another one from pin 3 to ground, to suppress noise.
Install the device on the white/orange (In pin 3, Out pin 5) wire that
enters the ECU.
The circuit operates a 50% duty cycle that is exactly 1/2 the frequency
of the speed sensor signal.
With this device in place, your ECU "sees" a vehicle speed of exactly
half reality. Theoretically, you can now do 270mph before you hit the speed
limiter.