I know this seems strange, but bear with me.

I'm using a TBI (donated from an 87 5.7L truck) on my boat. It runs great! However, I was having throttle follower issues where it doesn't come back to idle fast enough when I rapidly decelerate from a high RPM down to idle. I have not been using any type of speed sensor, so the signal is missing. Also, I do not use the park/neutral switch, so this system acts like a manual transmission. I've read that the throttle follower depends on feedback from the VSS to work properly.

The transmission in the boat is a 1:1 velvet drive. No shifting gears. The RPM of the crankshaft is the same RPM at the prop shaft. I thought if I used the tach signal to satisfy the VSS signal, my issues might go away. When I used the tach signal, the data lot showed 96 MPH when idling at 800 RPM. This was not real surprising.

So here is my question. Is there anyway I can trick the ECM or lower the pulses so the speed is closer to reality?

When I am running at 4600 RPM the speedometer on the boat reads 39 MPH (this is not linked to the ECM). The way I have this set up now the datalog would show 552 MPH at 4600 RPM.