Coasting in gear vs. neutral (fuel cut feature)

[roflwaffle]

Post up an A-B-A test with video, I've gotta see this!

[skyl4rk]

Originally Posted by kc7ekk

Before I messed with my scan gauge settings I was getting "9999" as the MPG during times of higher speed coasting. After setting "fuel cutoff" from 24 (default) to 0. My scan gauge was able to report back very high MPG readings without going into overflow mode (9999).

Does this affect the calibration at all?

In the past I did not use engine braking much at all, but did notice that I get 9999mph and 0.00gph when engine braking. I don't know if this is true. My previous habit was to coast in neutral as much as possible and pedal brake to a stop, and the scangauge showed about 0.25gph, and mpg was in the 200s and 300s, depending on how fast I was rolling in neutral in my Nissan Versa Base manual transmission.

Today I went out for a ride of about 80 miles. Instead of coasting in neutral all the time, I accelerated up to 5th gear (top gear) and anticipated stops using engine braking, leaving the car in 5th gear until almost ready to stop. I went down hills using engine braking where before I would coast down and exceed the speed limit and had to pedal brake.

This afternoon's ride was very nice due to lack of traffic (sticker shock at the pump?). For the most part I was able to drive 40mph with no tailgaters, in fact almost no traffic on the roads. I was very pleasantly surprised by avg mpg results, which was above 50 mpg (EPA is about 30). This is in part due to low speeds, but I think the engine braking strategy is an improvement over neutral coasting and pedal braking.

Caveat: this is based on a scangauge reading, and I question whether zero gas is being used when engine braking, I don't know if this is correct.

[justjohn]

Originally Posted by tjts1

While in DFCO I have it setup to automatically turn on the EGR valve and try to equalize the pressure between the intake and exhaust manifolds. This increased the distance I can coast in gear with injectors OFF.

This is cool. How did you do it? Would it be possible to set it so that it does it in 5th gear only so it wouldn't hamper actual engine braking?

[justjohn]

Originally Posted by skyl4rk

The real issue here is that coasting in gear (engine braking) is far more efficient than braking in neutral.

If you are truly coasting without the need to brake either at the moment or in the near future, coast in neutral. If you see a braking situation ahead, coast in gear.

Yes. Either way, this is the most important thing.

[tjts1]

Originally Posted by justjohn

This is cool. How did you do it? Would it be possible to set it so that it does it in 5th gear only so it wouldn't hamper actual engine braking?

I use megasquirt fuel injection which has several additional outputs that can be triggered by any number of parameters or combination of 2 parameters. The car came with a solenoid valve that feeds vacuum to the EGR in order to open. At first I played around with trying to eek out some FE under load by turning on EGR under specific situations but looking at my data logs, injector pulse width actually increased when EGR was on to maintain the same RPM at the same load. The only benefit i noticed is that the car coasts further on over run. So now the EGR is turned on only when TPS is at 0% (closed) AND RPM > 1500. All other situations EGR is OFF.
I haven't thought about limiting it to a specific gear. I would need to add an additional input to tell megasquirt what gear I'm in. Another option would be to turn the idle control valve to 100% duty cycle (wide open) when the TPS is closed but again, I have't tried it yet. The EGR is easier to trigger.

[euromodder]

Originally Posted by skyl4rk

I went down hills using engine braking where before I would coast down and exceed the speed limit and had to pedal brake.

That's a situation were engine braking should be used, as coasting leads to excessive speed.
Of course you'd be using less gas as well.
With engine braking, the fuel flow gets cut off.
With coasting in neutral, you're still using gas (and the brakes).

I think the engine braking strategy is an improvement over neutral coasting and pedal braking.

They aren't mutually exclusive.
Use the best option for the varying circumstances.

I often end coasts with a bit of engine braking.
Partly because I still overshoot the target / underestimate the coasting distance, partly because I don't want to keep up other traffic too much by crawling to a turn or light.

When you have to slow down faster than coasting will allow for, engine braking is the way to go.

[RH77]

I came across something by accident this week, and I wonder if it's worthy of continuing:

Vehicle: '98 Integra Automatic
Manual Torque Converter Switch: On (using battery power)
Auto Trans Selector: Drive (D4)
Ignition: Off

Things got busy on a downhill, curvy road at about 35 mph (with no power steering I had focused on the steering effort and was distracted by a partial lane closure, which resulted in ignition-off while still in TC lockup and in gear -- too busy watching the road completely and not the instrumentation). The obstacle was not a factor and the downhill run continued.

The EOC and manual TC and shifting process has become so routine in my mind, that I no longer have to think about it. So the pattern continued as if it was not interrupted. I thought I had shifted into Neutral for an engine-off coast, but instead went up to D4 (one away from N). Here's where it gets interesting. I sometimes give the gas pedal some pumps during EOC (out of boredom perhaps, since it doesn't do anything -- like to the beat of a song or something -- or "pretend floor it" through yellow lights while coasting-- and no I don't run reds). But this time it did do something interesting...

I heard the open intake resonance during the pedal pumps, then it upshifted from 3rd to 4th. Now the transmission was operating without the electronic control unit, and only by mechanical measures and throttle cable input. The TC remained locked, turning the crankshaft like a manual transmission would. I keyed-back to "on" and the injectors didn't skip a beat. This was great!

Naturally there is compressive deceleration, but it is considerably lessened with WOT to introduce air to pump through. Shifting from D4 to D3 does nothing, but I can shift into "2" and it downshifts, so now I can utilize more aggressive engine braking (not being able to rev match bothers me a little), so I wait and left-foot brake if necessary, until the torque potential is low enough to downshift without too much strain on components. Slowing to a stop, I have been varying throttle inputs to hear engine RPM since the SG and tach are off. The funny thing is that it sounds like a Jake Brake at WOT approaching a stop.

If it looks like traffic will begin to move, I quickly have to disengage the TC and key-on (or else the transmission will perform a double-shift hunt or halt the engine). Then when up at the proper speed, the TC is re-engaged and off we go.

Coming to a complete stop with the unknown timeframe to move again, requires fast action. To prep for start, I have to move the lever from 2nd up to Neutral (a quick push forward stops it there without using the release button or having to look at it), then I flip the TC switch off and the engine stops smoothly. Waiting too long for either step, results in bogging and vibrates the engine similar to keeping a manual in gear too long before pressing the clutch pedal and the engine can be felt "stalling out" with a shudder. On the contrary, performing the measure too quickly will stop the engine and not offer the convenience of just turning the ignition key for instant operation.

So, should I be excited with my new-found "manual transmission" and Jake Brake? (OK maybe not the latter -- the resonator was removed to source warmer air, and was only heard during higher throttle openings (rare), until now when it doesn't use any fuel -- it's obnoxious and confuses onlookers).

Being able to key-on and go is great. If this works well, I imagine having an injector kill button (a simple SPST) on the shifter stalk so I don't lose everything electrical (SG, tach, radio, blower fan, SRS, wipers) and then just release the button to re-energize.

I'm running though it in my mind how this would/wouldn't damage the transmission. Another advantage is that it circulates the engine coolant to prevent hot spots. As I understand it, TC lockup is the safest situation for a transmission -- pumps can turn, and heat doesn't build-up. Downshifting with the TC engaged is generally pretty firm (upshifts too during engine-on), which can have a lasting effect on other torque-sensitive driveline components and the engine itself. AFAIK, having the engine running, or off and locked-into the trans is virtually the same thing.

Am I missing something? Is DFCO a better way to go or just EOC in Neutral and crank the starter? In most cases that I have been using it, is to decelerate and be able to re-start quickly and not have to rev-match back into gear

[Hauki]

Friction is the enemy, so why DFCO and have all that drivetrain friction going on? It creates un-necessary friction & heat loss in the transmission & clutch (in manual cars).

So why not put it in neutral and let the car free fall so to speak?

Coasting in neutral has massively improved my FE since I started using it.

Yes when the car is on tickover it uses tiny amount of fuel, but it more than offsets the energy absorbed by the drivetrain on DFCO.

Maybe DFCO works up to 40MPH, but then engine braking kills any benefits and its over to CIN (coast in neutral).

I only wish I'd employed it a long time ago well you live and learn!

[Arragonis]

When I am coasting downhill I can use a high gear and take advantage of DFCO. If I am coasting on a shallow slope or on the flat I use neutral. I have experimented with engine off but don't use it. These have given me an instrumental increase in MPG but not a huge tank to tank one yet.