I am using a GM fuel injection system on my boat and want to make it run seamlessly. I designed a circuit to supply the ECM with a VSS signal and a P/N ground signal. It consists of a 5v power source, 2 relays, 2 transistors, and a divide by 12 IC. Since I have no way of integrating a real speed sensor and actual speed is not an issue, I compromised and hope that this circuit will tell the ECM that the boat is going 1 MPH per every 100RPM that the engine is turning while in gear. Here is the math; tach 4 pulses per rev * 100RPM * 60min / 12(divider IC) = 2000 pulses per mile. One Transistor is used to condition the tach signal into a 5v square wave form. The other transistor is used to deactivate the VSS circuit (show 0 MPH) and provide a P/N ground through the relays. This transistor is activated by grounding through the boats neutral safety switch and through the starter solenoid's coil. If there is anyone out there who is interested or knows anything about electronics please feel free to have a look at the circuit and tell me if you see any issues with it. Thanks for the feedback.

 

Why not just delete the code? What Ecm are you running?