Coasting with a Slushbox

[2TonJellyBean]

When coasting with the engine on:

I've heard others claim that coasting in drive is more efficient because the injectors cut off, but I can't see the engine being dragged in a non-burning state for very long, and the glide is much much longer in neutral. I have been coasting in neutral and think I get better FE that way.

Does anyone have a good link that explains how FI systems work on cars with and without automatics when they are coasting?

[SVOboy]

I think automatics usually leave the injectors on, at least mine used to...but I can't get more technical than that.

[omgwtfbyobbq]

It idles.

[2TonJellyBean]

I trust everyone's judgment and appreciate your responses but are there any good links that you know of?

[skewbe]

Sure, http://www.gassavers.org/search.php

Really it depends on who was doing the programming on that car. Some leave fuel running, some dont, some even add extra fuel. It varies by model. If you want to be sure then you have to monitor the pulses sent to the injector under various conditions.

[rh77]

Originally Posted by 2TonJellyBean

I trust everyone's judgment and appreciate your responses but are there any good links that you know of?

Not to be rude,
or a party pooper,
or a poor ombudsman,

but there are some experiments and/or threads here at GS that address this very data inquiry.

Over 2K RPMs, autos generally cut fuel in D. In N, it idles and uses fuel.

[cfg83]

2TonJellyBean -

Originally Posted by 2TonJellyBean

I trust everyone's judgment and appreciate your responses but are there any good links that you know of?

Sorry to say I don't have a good link either . What does your SG-II say when you are coasting? If MPG goes to 9999, then it is *very* likely that your ECU/PCM is turning off the injectors. When I was in Europe, I saw this behavior with the (stickshift) Diesel I was driving.

From my POV, this is a drivetrain specific question. Different cars operate differently. If you drove a Saturn, I would mooch diamondlarry for what his FSM (service manual) says.

CarloSW2

[omgwtfbyobbq]

Oh yeah. When coasting most will inject/essentially idle in gear only if the engine speed is below a certain point called DFCO. This point depends on coolant temperature, RPM and the throttle position IIRC, but it's over a fixed range. Even if it isn't idling in gear, the car may send a bit of gas through to keep the catalytic converter warmed up, but it isn't a whole lot.

Edit- Too slow!

[2TonJellyBean]

With my vehicle it comes down to either losing speed quickly but not burning fuel during the DFCO phase, or coasting longer and keeping the inertia/speed but having to keep the engine at idle using 1/3 GPH. Neutral "seems" far far more efficient. I've seen nothing in the way of any studies that can empirically back this up. Sorry if I'm dense on this guys...

cf, you could check your SG and see if it goes to open loop on decel. If it does that's proof the DFCO is taking place.

[cfg83]

2TonJellyBean -

Originally Posted by 2TonJellyBean

With my vehicle it comes down to either losing speed quickly but not burning fuel during the DFCO phase, or coasting longer and keeping the inertia/speed but having to keep the engine at idle using 1/3 GPH. Neutral "seems" far far more efficient. I've seen nothing in the way of any studies that can empirically back this up. Sorry if I'm dense on this guys...

cf, you could check your SG and see if it goes to open loop on decel. If it does that's proof the DFCO is taking place.

Ok, I will do that tonight and give you an update.

I'd never heard of DFCO until now :

DFCO = Deceleration Fuel Cutoff

Maybe we should add it to the FAQ :

GS FAQ/Glossary, Busted/Confirmed Mods, Archive
http://www.gassavers.org/showthread.php?t=1088

My overall POV on this is that each has it's place in hypermiling. If the car features DFCO, then this can be used as a tactic for increasing MPG when you need to slow down because of traffic. If you're going to lose all that precious speed, you might as well turn off those injectors.

CarloSW2