I have a 2001 mercury 150 EFi. When I start the motor, if the tachometer isn't working, it won't work the whole time on that run from spot to spot. But if I start the motor and the tachometer is working, it will work until I shut the motor off. It's been doing this for a couple of years. And it only works 1 out of 10 times. Any help would be appreciated.