How do I know if my car uses DFCO?

[Detail Man]

So I've been reading up on P&G techniques and the pros and cons of coasting in neutral, clutch in and clutch out. Anyway, the issue of whether or not the car employees DFCO comes in to play. I assume that my 2005 Chevy 2500HD Silverado (auto trans) uses DFCO, because after topping a hill and letting off the pedal, the tach goes to idle as I go down the hill (coasting in gear). This is DFCO in action, correct?

How can I find out if my 2002 Honda Civic LX (5sp manual) uses DFCO? (FYI: I have been coasting in neutral with the engine on mostly, but have begun experimenting with EOC.) When I let off the pedal and remain in gear the tach still shows 2000 rpm in 5th (for example). But if I slip into neutral at the same speed, the tach shows about 800 rpm idling. I imagine when I get a Scangauge/Ultragauge I'll be able to measure the difference in fuel consumption, but I don't have one just yet (still trying to decide on which one/saving up). If there is no DFCO at play, then I'm using less fuel coasting in neutral at idle, correct? But if the civic uses DFCO which is the best technique?

[vskid3]

Staying in gear and using DFCO will slow you down much faster than coasting in neutral. You'll probably end up using more fuel if you try to pulse and glide with DFCO vs cruising at a constant speed.
The reason the RPM's stay at 2k when you let off the gas is because its a manual. Unless you do something to disconnect the engine from the wheels, like pushing in the clutch, the RPM to MPH ratio will always be the same for each separate gear no matter what you do with the brake or gas pedal. If you RPM's dropped when you let off the gas, you would have major issues. Also, RPM's aren't a very good gauge of fuel usage.
I'm 99% sure your Civic has DFCO. My '97 did, and I see no reason why they would have gotten rid of it. One way to test it is to try turning the ignition off while doing what you think is DFCO and seeing if there is a difference in engine braking force. If there is no difference, then you have DFCO. Because some cars are more picky than others about when they'll do DFCO and to be able to feel the difference between ingnition off/on if there is one, make sure the RPM's are over 2k and you're in 1st or 2nd gear when you do the test. Be sure to be safe, too, and do it in an empty parking lot or road.

[Joggernot]

Get one of the gages. Above 42 mph, quickly lift you foot from the throttle and watch the instantaneous mpg on your SG. After a couple seconds it will read 9999 if you have DFCO.

Without the gage, vskid3 gives the easiest method.

[user removed]

DFCO will kick off about 11-1300 RPM. Let the car slow down in gear and when DFCO ends you will feel the difference, since the engine will stop braking the car.

regards
Mech

[roosterk0031]

The Auto truck won't DFCO, unless you put it indo D maybe 2 to get engine braking, GM unlocks the torque convertor with their autos when in OD so they coast better so you'll never get engine braking or DFCO in OD.

I don't know what the towing button would do, maybe it would keep it locked thinking you would want engine braking then.

[user removed]

Tow light probably prevents torque converter lockup or high gear selection. Neither good for MPG. I would use it for engine braking when you get caught and have to stop quickly.

regards
Mech

[96CX]

Originally Posted by Detail Man

So I've been reading up on P&G techniques and the pros and cons of coasting in neutral, clutch in and clutch out. Anyway, the issue of whether or not the car employs DFCO comes in to play. I assume that my 2005 Chevy 2500HD Silverado (auto trans) uses DFCO, because after topping a hill and letting off the pedal, the tach goes to idle as I go down the hill (coasting in gear). This is DFCO in action, correct?

No. That is your automatic transmission sensing no engine load and shifting to neutral to allow coasting.

Originally Posted by Detail Man

How can I find out if my 2002 Honda Civic LX (5sp manual) uses DFCO? (FYI: I have been coasting in neutral with the engine on mostly, but have begun experimenting with EOC.) When I let off the pedal and remain in gear the tach still shows 2000 rpm in 5th (for example). But if I slip into neutral at the same speed, the tach shows about 800 rpm idling. I imagine when I get a Scangauge/Ultragauge I'll be able to measure the difference in fuel consumption, but I don't have one just yet (still trying to decide on which one/saving up). If there is no DFCO at play, then I'm using less fuel coasting in neutral at idle, correct? But if the civic uses DFCO which is the best technique?

DFCO happens when you are in gear and let off the gas to use engine braking. If your tach shows idle, then DFCO is not happening.

[RobertISaar]

Originally Posted by roosterk0031

The Auto truck won't DFCO, unless you put it indo D maybe 2 to get engine braking, GM unlocks the torque convertor with their autos when in OD so they coast better so you'll never get engine braking or DFCO in OD.

I don't know what the towing button would do, maybe it would keep it locked thinking you would want engine braking then.

they'll still kick into DFCO in 4th gear if at a high enough speed. it doesn't happen as quickly as in 2nd/3rd gear, but it will happen if certain conditions are met.

tow mode modifies shift points and TCC lock/unlock behavior.

[RobertISaar]

Originally Posted by 96CX

No. That is your automatic transmission sensing no engine load and shifting to neutral to allow coasting.

the transmission is incapable of shifting into neutral without the shifter physically being moved.

what is happening is the torque converter is unlocking and allowing the driven portion(transmission side of converter) to overrun the driving portion(engine side of converter).

if the torque converter were commanded to lock/stay locked in there events, engine speed would remain the same as before letting off of the throttle, which will cause noticable engine braking compared to an unlocked converter coasting with much less engine braking.

[Detail Man]

Thanks for the info guys. I'll have to try out the vskid's test tomorrow and see if I can tell a difference in the civic.