Fuel Cutoff question

[hybriDatsun350]

Originally Posted by 8307c4

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

I'd like to know where you got your numbers? My Integra definitely cuts fuel on deceleration. It keeps the injectors off all the way down to about 1100 rpm.

[theholycow]

It does help enough to be worthwhile. How does it increase your risk of hitting reverse? Don't you have PRND21?

Make sure you confirm the behavior at all speeds where you might use it.

Don't use it in place of neutral coasting when you don't intend to stop or slow down...the total amount of energy saved is more in N in that case.

[zimagold]

Originally Posted by theholycow

How does it increase your risk of hitting reverse? Don't you have PRND21?

As I come to a stop, I'll want to be in neutral to either idle or shut off the engine. But going from 2 to N - if I just push the shifter without using the button, it makes a loud clicking noise which I don't like. So I will more often push the button in to shift, which will disengage the lock-out to reverse. Hasn't happened yet, but from what people say here, it's bound to happen once you start shifting automatics more.

[severach]

My 1994 Grand Am with Quad 4 does DFCO when the mph starts above 55, the TCC is locked, and the gas pedal is off. DFCO never occurs when the TCC is disabled which is any speed 44 mph or less.

DFCO is not hard to detect in an automatic without any instruments. It just happens less often. With DFCO the car will have two different deceleration rates. It will start with idle deceleration then when the ECM determines that all the right conditions are met is the fuel is cut off which will be a stronger deceleration and the engine noise may change.

[Chibougamou]

I use the DFCO ICE-on with my 2002 Honda Civic (auto) all the time. Without it, I'd get around 40-42mpg at about 55 mph trying to minimize the LOD engine load factor (so slowing down going uphill, speeding up going downhill, more or less dead-pedal).

With DFCO ICE-on, I "porpoise" 10 seconds on (75-85% engine load factor per Scan Gauge II), and try and maximize the glide (although it is usually about 5-7 seconds, in moderate to heavy traffic). In spite of the lob-sided 10-on, only 7-glide numbers, I get around 48 mpg that way on the highway, cycling between a low of 55 mph to 60 mph. There's nothing magic about 10 on and 6 off --- just seems easier to do and keep up with traffic.

The porpoising also encourages tailgaters to get around you, cause their cruise control doesn't match with your "porpoising" (p & g).

While there IS a bit more drag with DFCO ICE-on than coasting in N with ICE-off, the difference is not THAT noticible. Most passengers don't even realize that I am porpoising --- the accelleration and decelleration are blended that smoothly, most of the blending work done by the auto tranny, not me.

DFCO ICE-on is wasted in town, below about 35 mph in my case. At low speeds you get about 15-20% further glide with ICE-off in neutral, as the 9999 readings disappear at lower speeds (sub 30 mph in my case, regardless of the tach reading --- that probably is different with different cars, though).

I recently changed the tires from 185/65 R15's to 205/65 R15's (so increasing the rolling diameter by 4.5%) and this adds another 2 mpg over the numbers I've reported above. Whoopie --- over 50 mpg with an auto Civic!

Hope this helps

[Ford Man]

Originally Posted by k8crd

Can you check with a Scan-gauge II if your vehicle has fuel cutoff?

If yes, what is the procedure?

Paul

What kind of car are you driving? I would be relatively certain if it's a Ford that has been make in the last 20 years the answer is yes, because my '88 Escorts both have DFCO. On my '97 Escort when I first installed the Scan Gauge I would get readings of 9999 sometimes, but then for some reason it started reporting high mileage figures varying with speed when I'm not on the accelerator. I've heard of this happening to others too. So I know it does have DFCO.

[theholycow]

Originally Posted by Chibougamou

While there IS a bit more drag with DFCO ICE-on than coasting in N with ICE-off, the difference is not THAT noticible. Most passengers don't even realize that I am porpoising --- the accelleration and decelleration are blended that smoothly, most of the blending work done by the auto tranny, not me.

With an automatic, that technique (which I call "Pulse & DFCO") could work, assuming that the torque converter is unlocked during the DFCO phase. I believe that it would still be more efficient to coast in neutral with the engine on (which I call "Pulse & Glide"). I'm glad to hear that is does work for you.

You should not coast in neutral with the engine off (which I call "Engine Off Coasting", "EOC", or "Pulse & EOC") with an automatic transmission. Most automatic transmissions are designed in such a way that doing so could cause damage.

[Chibougamou]

"You should not coast in neutral with the engine off (which I call "Engine Off Coasting", "EOC", or "Pulse & EOC") with an automatic transmission. Most automatic transmissions are designed in such a way that doing so could cause damage."

Thanks for your caution, however the 2002 Honda Civic autos are fine for coasting with the engine off, and the tranny in neutral. (I can't speak for other years or other models). I've done it for years, and haven't had any problems with my Civics. The most common way of verifying this is to make sure the brand and model of car can itself be towed. In this case see:

http://www.irv2.com/forums/f85/03-ho...wing-7962.html

The more serious concern is that EOC with most cars kills the power steering (the civic is pretty light, but you have to horse it around curves), and the brake pedal has enough umph for about 2 minutes of constant light braking, and then you better turn the engine on, quick! Again, I've had a lot of experience with both phenomena.

Using an automatic, I'm not happy with cycling between EOC pulse, and then going to neutral, and back --- that works great on a 5 speed MT, but that's much tougher on the torque converter in the AT tranny, which has to match higher rotational speeds. So for an automatic the porpoising seems to be a reasonable compromise that gives 50 mpg results at 50-60 mph.

[theholycow]

You are correct, checking to see if it can be flat-towed is how you find out if it can EOC. That's good to know about the Civic's transmission. How were you restarting from your EOC? I've heard of bump-starting automatics but I imagine that's a quick way to break stuff.

If you're electric starting or if you're leaving the engine on, there's no reason that the torque converter or the transmissions's clutches need to match any rotational speed at all; you can simply rev-match it with the gas pedal before shifting into D. That's what I do in my automatic, just like in a manual.

Also, as far as higher rotational speeds - the Civic's automatic is geared lower than its manual? Most cars have a taller high gear in their automatic than their manual.

[Chibougamou]

"How were you restarting from your EOC? "

I use extended EOC around town, often on Rat Runs (side roads that are lightly travelled), where I go for LONG coasts in neutral, ICE-off, and short bursts at 80% LOD (engine load factor). Typically 10 second bursts and 30 second plus EOC (where I can get away with it --- the wife's patience usually being the limiting factor).

For low speeds, I just key the motor off to the Run-I detent (and don't bother going back to the Run-II detent --- so, no gauges active, and limited Scan Gauge even on hybrid setting, but I don't have the headlights draining the battery either --- remember we have automatic headlight on in the Great White North). Restart under 15 mph is no problem.

For interest, I do have a 15 watt solar panel in the back window, plugged into the cigarette lighter. Seems to work well at keeping the battery topped off.