2008 minivans: Honda Odyssey vs Toyota Sienna

nope. the engine is turning because it's in gear and the weight of the
vehicle is pushing it down hill. in this situation, the computer will
inject zero fuel. not one drop. [unless you put your foot on the gas
again of course.]

go to megasquirt.info, dig through until you find the source code, read
it, and there you will see an example of the shut-off, and the
parameters the computer uses to do it.

 

Ya got me there. I can't remember what the pumps were that far back. I
wasn't even hear driving yet!

-Dave

 

Your take on that is completely wrong. In this case, the engine is
being driven by the transmission. No combustion is taking place. The
engine runs on the energy of the downhill glide until your RPM's get
low enough that the fuel needs to be injected again to keep the engine
running.

 

OK. Makes sense I guess.

 

On Wed, 23 Jul 2008 06:00:57 -0700, jim beam

snip

I agree I am nit picking now but a closed throttle and high rpm (plus
750-1500 rpm I think you said) is not quite the same as torque
reversal although it is certainly indicative.

This, for me, has been a very intertesting exchange and I thank you
for you explanations and patience.

 

Toyota Sienna LE 7 passenger
What did it for me was AWD, 266 HP and 245 lb.ft. of torque @ 21/30 MPG...

a

 

The point is that the ecu doesn't *need* to detect "torque reversal" to
know when to shut off fuel. All it needs is RPM and throttle position.

a

 

Not at all. think about it - take the engine out of the car and put a
handle on the crank - you can turn it with your own hand! Why is it hard
to believe that thousands of lbs. of moving car can't do that? The
friction of moving turning the engine without fuel is what slows you down
when gearing down. It's often good practise to be in a lower gear and off
the throttle when descending a steep hill - the engine resistance will slow
you or keep you at a constant speed. If there were fuel being fed to the
engine to "keep it running" then there would be no braking effect.

NB: I know this is the case with a manual transmission, but IIRC, there are
instances where an automatic still feeds a tiny amount of fuel during
"rundown".

a