The tach dropping out while underway in gear may mean you are losing
hall pulses or the ECU is losing it's power or ground connection.

Yes, the ECU can have a partial failure. There are hundreds of
electronic components inside, divided into different functions. A
function could get out of whack or die entirely while the rest
unknowingly carried on like nothing was wrong.

Mark

Raymond Paquette wrote:
> Pretty much, although it doesn't have time to get to zero before the engine
> kicks back in.
>
> snip------- You mean the tach drops all the way down, while gear is still on
>> and
>> van going forward, but slowing ?-------snip
>>
>>