coasting a GM in neutral not economical?

[comptiger5000]

Most modern vehicles have DFCO, although the parameters for how they use it may not be ideal.

[Phantom]

Most if not all GM have DFCO but the settings are not set the best on the vehicle. My 03 Grandprix can go into DFCO much easier than my 98 Bonneville both have the same settings for DFCO but the Bonneville has taller gears so I'm not always above the needed RPM to enable DFCO when letting off the gas.

If you can see when the vehicle goes in to closed and open loop then look for that if going down a hill and the throttle is at 0% when doing 65mph after 2-3 sec the PCM should go into DFCO if the revs were high enough to the gear. If it does not go into DFCO (indicated by open loop) try again and down shift this time and see if it happens.

[darcane]

Originally Posted by Thymeclock

Both. With use comes wear, and everything wears out eventually.

Wear can be minimized by proper driving habits, but not eliminated. Brakes, as I mentioned, are a better example. The more you have to brake, the sooner your brakes will wear down. If you ride the brakes you will cause premature brake wear. But most braking is an unavoidable necessity.

And in both cases, they only wear when there is a difference in speeds. Your brakes are not getting worn down when your car is stopped and you have the brakes on. Similarly, your clutch is not getting worn once it is fully engaged and you accelerate or cruise in gear and there is minimal to no wear if you rev match between shifts. The vast majority of the clutch wear comes from getting started from a stop.

[darcane]

In my GM truck, I see far better economy by coasting in neutral than engine braking with DFCO (if it's even on mine). I'll stick with Neutral coasting, thank you.

[roosterk0031]

Tried this with my 03 Malibu auto last night and this morning. Only time I could get the scangage to go 9999 so fuel is cut off is downshifting into 2nd while still going 40ish so 2500+ rpm and lots of engine braking. While costing down a long hill this morning couldn't see a much difference between costing in netural or OD watching GPH either way was 0.39 plus or minus 1/100.

[PaleMelanesian]

That whole article is full of FUD and straw men. Don't waste your time reading it.

AC vs windows - didn't test with windows up and AC off.
DFCO - already covered
reduce weight - obvious
inflate tires - obvious
roof rack - obvious
engine off at stops - looks like a sales pitch for hybrids that do it for you
convertible top up - obvious, but how many people drive convertibles?

[abell75]

Originally Posted by Phantom

Most if not all GM have DFCO but the settings are not set the best on the vehicle. My 03 Grandprix can go into DFCO much easier than my 98 Bonneville both have the same settings for DFCO but the Bonneville has taller gears so I'm not always above the needed RPM to enable DFCO when letting off the gas.

If you can see when the vehicle goes in to closed and open loop then look for that if going down a hill and the throttle is at 0% when doing 65mph after 2-3 sec the PCM should go into DFCO if the revs were high enough to the gear. If it does not go into DFCO (indicated by open loop) try again and down shift this time and see if it happens.

I don't have a scangage and won't for a while...I'd like to know if there is a way to confirm that a vehicle is using DFCO based on information available while driving the vehicle under stock conditions.

Most cases when I drive without using throttle (can't just say 'coast' lol) there is a stop sign or light ahead, but in a few cases I will speed back up. Knowing if I should stay in gear or not would be useful info!

Thanks in advance.

[Thymeclock]

Originally Posted by abell75

I don't have a scangage and won't for a while...I'd like to know if there is a way to confirm that a vehicle is using DFCO based on information available while driving the vehicle under stock conditions.

I'm not sure of how you would know even with a scangauge. Would anyone know?

Most cases when I drive without using throttle (can't just say 'coast' lol) there is a stop sign or light ahead, but in a few cases I will speed back up. Knowing if I should stay in gear or not would be useful info!

Thanks in advance.

Assuming you have an automatic transmission: my rule of thumb is to coast in neutral when approaching a stop sign. You need to stop anyway, and the car will roll further when not in gear. If I'm approaching traffic light however, I stay in gear because it allows me to maintain speed or accelerate if needed. It is questionable whether some transmissions can be shifted from neutral in to drive at higher speeds without incurring damage to the transmission.

[abell75]

Originally Posted by roosterk0031

... Only time I could get the scangage to go 9999 so fuel is cut off is ...

Originally Posted by Thymeclock

I'm not sure of how you would know even with a scangauge. Would anyone know?

From the Scangage II manual:

Some vehicles will turn the fuel injectors off when coasting. This will
cause the fuel economy to go to 9999 MPG or 0.00 KHL. This shows
when you are not using any fuel while coasting.

Originally Posted by Thymeclock

Assuming you have an automatic transmission: my rule of thumb is to coast in neutral when approaching a stop sign. You need to stop anyway, and the car will roll further when not in gear. If I'm approaching traffic light however, I stay in gear because it allows me to maintain speed or accelerate if needed. It is questionable whether some transmissions can be shifted from neutral in to drive at higher speeds without incurring damage to the transmission.

My thinking is that if I'm going to stop anyway, then not using fuel when coasting to the stop is better than coasting in neutral because in neutral you need to use fuel to keep the engine running (assuming you don't shut off the engine - most of my coasts are too short for this). I won't coast as far, but that just means I use the brakes less.

So if fuel goes to zero, I'll leave it in gear. If the injectors keep supplying fuel anyway, then I'll put it in neutral so I can let off the throttle sooner.

[Phantom]

Sorry I have not been around as much. The easiest way for me to tell when it is in DFCO is the car switches to open loop mode. On the Grand Prix Open Loop is only used when 1. start up, 2. High throttle, 3. DFCO, 4. When MAF is dead.

Without a scanner its hard to tell what it is doing as you cant feel if in DFCO.

As for being in gear or Neutral here is how I do it.
In Gear if:
Speed is under 27mph.
If it can't stay in N for atleast 10sec (Fuel use increases for a sec or two on the shift in/out of N.)
If I will be stopping or accelerating soon.

N is used in all other situations but mostly down hills or long shallow slopes that I can maintain speeds on. A tip for that trans is let off the gas for a sec before going to N and when shifting back to Drive lightly press the gas if your speed is >63mph that way the TCC does not need to compensate for the needed increase in RPM (rev match the shift).