Myth dispelled?

[ORCoaster]

theman53.  I have a TinyTach on my car and a fair downhill on my run to work.  I don't see the drop you mention.  It holds pretty much at the same RPM I had at the top of the hill.  Are you saying I should downshift and engine brake down the hill and I will see the tach drop down as well? 

The Tach does have that Piezo pickup on it.  Works great with the Mac Tool when I had it. 

I think the injectors still fire and the pick up senses that.  What changes is that there is little fuel being pushed at the injector as the foot is off the throttle. 

I might have to experiment over the next couple of days and watch what is happening with the numbers on the tach.

[TimpanogosSlim]

on modern gassers with common rail electronic injection, it does just stop bothering to fire the injectors, because it can. and the instantaneous mpg calculator in the cluster just displays "- -".

[theman53]

theman53.  I have a TinyTach on my car and a fair downhill on my run to work.  I don't see the drop you mention.  It holds pretty much at the same RPM I had at the top of the hill.  Are you saying I should downshift and engine brake down the hill and I will see the tach drop down as well? 

The Tach does have that Piezo pickup on it.  Works great with the Mac Tool when I had it. 

I think the injectors still fire and the pick up senses that.  What changes is that there is little fuel being pushed at the injector as the foot is off the throttle. 

I might have to experiment over the next couple of days and watch what is happening with the numbers on the tach.

I don't know personally, I think it was Rabbitman that had a video on here years ago. The video showed where he let off and slowly the numbers fell, even though the engine was not slowing down that much, until it would stop showing numbers. I don't know what hill he used or gear. IIRC he did say that you had to be over "x" rpm for it to work. Which would make sense as not much time to see rpm drop from say 2,500 to idle or 1,500rpm.
This video shows a little with the gov weights and you can kind of get an idea of how it works.
https://www.youtube.com/watch?v=vyi9dOj3HkM

[vanbcguy]

Coasting downhill in gear with my engine will often result in EGTs around my coolant temperature - I'll see EGTs drop down as low as 75-80C.  There can't be much fuel burning in there at all at that point.

[ORCoaster]

On the scan gauge I get 9999 in place of the mpg when I coast downhill and the foot is off the accelerator.