injector fuel cutoff during decel

[timjb31]

Since my VW has a digital instantaneous mpg readout, I can see what is going on with fuel consumption. Shortly after purchase, I realized that when coasting, no throttle, manual transmission in gear, that the computer cuts ALL fuel to the cylinders depending on initial rpm when throttle is released. From what I can tell, rpms should be about 2000-2300 when initiating the fuel cutoof sequence (may need to downshift a gear or two). Fuel wil remain cut off until rpms drop below about 1300, at which point you feel a slight jerk in the drivetrain and the mpg readout goes from infinite to something in the 50-80mpg range (idling while coasting, depends on speed and idle consumption rate). During hte cutoff period mpg is far superior to coasting while idling, and equal to cutting the engine off entirely (but without the extra wear of restarting). While you are not "recapturing" energy in the way a hybrid does with regenerative braking, you are taking advatage of the kinetic energy that has been built up, so it has an alnalagous result (though perhaps smaller).

I was wondering of other makes/models have a similar mode? Or is it particualr to VWs? I can't tell onthe Bimmer, because it has an analog mpg gauge (probably a "calibrated" vacuum gauge!).

TJ in MD

[diamondlarry]

I think I've heard that some Honda's do this as well as some Toyota's.

[BailOut]

Here's a writeup I did on DFCO:

http://www.yarisworld.com/forums/showthread.php?t=4248

[southerncannuck]

The Honda Fit shuts off the fuel when coasting.

Louis B

[lightfoot]

My understanding is that the Insight does this as well, though the mpg maxes at 150mph either way, so it's hard to tell without switching the display to liters/100km.

This is a great method to use if you are coming to a stop where you will not shut off the motor, or going down a steep hill where coasting in neutral would let your speed build up too much.

But the compression of the engine will slow the car much faster than coasting in neutral engine on or off. You can minimize this compression braking by staying in a higher gear, but that means that idle will cut in at a higher speed.

So if you are in a situation where you want to max your coast distance, then putting it in neutral ICE-on or -off might net you better mpg. If you expect to stop for a while (say at a light which has just turned against you), it might be worth considering turning off the engine as you pop it into neutral to begin your coast.

I try to avoid decel in gear because it quickly becomes a habit for me. I find myself using it just to modify my speed slightly when a better mpg strategy would be to coast in neutral and touch the brakes if needed.

[Blake]

I've been using regen to help charge up the battery pack when coming to stops while getting into fuel cut.

Both will happen at the same time, although you do slow faster than normal. I leave it in a high gear and when idle cuts in, I downshift to get back into fuel cut and regen.

I'm sure FASing would be more benifical, but I only do that when the pack is mostly charged.