Getting the Tacho to work correctly

Whilst the engine worked the tacho didn’t move at all. Reading up on the LS1 forum this seems to be a common problem with post 2003 GM ECU’s. Instead of a 12V pulse signal the pulse goes to -1.5V from 0V. In order to correct this most people use a pull up resistor (10K ohm) connected to the 12V. There are a couple of horror stories though about people frying the ECU using this method. I opted to play it safe and build a small circuit to buffer the signal. I then used a pull up resistor with only a risk to the 50p inverter chip. This worked a treat and the tacho now works perfectly

Whilst I was at the modification I decided to modify the wiring to that in future we were able to start the engine through the use of a couple of switches (rather than touching wires to the battery.)


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